HIM
EPA-SAB-74-001
May 1974
HERBICIDE
REPORT
Chemistry and Analysis
Environmental Effects
Agricultural and Other Applied Uses
HAZARDOUS MATERIALS
ADVISORY COMMITTEE
SCIENCE ADVISORY BOARD
U.S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.C. 20460
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PURPOSE AND FUNCTIONS OF THE
HAZARDOUS MATERIALS ADVISORY COMMITTEE
of the
U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
The Hazardous Materials Advisory Committee is one of several scientific public advisory com-
mittees which make up the U.S. Environmental Protection Agency Science Advisory Board. This
committee consists of a group of scientists from outside the Agency, assembled to provide the
Administrator and other Agency officials with independent scientific advice on problems facing the
Agency. The functions of the committee are to advise on scientific and policy matters pertaining to
hazardous materials in the environment; make recommendations concerning needed research and
monitoring activities; assess the results of specific research efforts; assist in identifying emerging
environmental problems related to hazardous materials; provide advice with respect to scientific
aspects of the Agency's relations with other governmental agencies, citizen groups, industrial groups,
and educational institutions; recommend policies with regard to appropriate control of hazardous
materials; and provide review and recommendations for research and research training grants in the
areas of radiation and water hygiene pursuant to the requirements of Title III of the Public Health
Service Act, as amended.
This document is available in limited quantity through the U.S. Environmental Protection
Agency Science Advisory Board (A-101), Room 1018, Crystal Mall 2, 1921 Jefferson Davis Highway,
Arlington, Virginia 20460. Additional copies are available to the public for purchase through the
National Technical Information Service, Springfield, Virginia 22151.
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EPA-SAB-74-001
MAY 1974
HERBICIDE REPORT
Chemistry and Analysis
Environmental Effects
Agricultural and Other Applied Uses
by the
HAZARDOUS MATERIALS ADVISORY COMMITTEE
United States Environmental Agency
Washington, D.C., 20460
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EPA NOTICE
This report has been written as a part of the activities of the Hazardous Materials Advisory Com-
mittee and was initiated prior to the establishment of the Science Advisory Board, of which it is a
member committee. The Science Advisory Board is a public advisory group providing extramural
scientific information to the Administrator and other officials of the Environmental Protection
Agency. The Board is structured to provide a balanced expert assessment of the scientific matters
related to problems facing the Agency. Because this is an independent, extramural report, the Agency
has no role in its review and approval. Hence, its contents do not represent the views and policies of
the Environmental Protection Agency, nor does mention of trade names or commercial products con-
stitute endorsement or recommendation for use.
11
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PREFACE
The Hazardous Materials Advisory Committee (HMAC) was asked to prepare a comprehensive
report on herbicide uses and their environmental effects. The study was to serve as a background for
EPA decisions.
The study was first inaugurated in May 1972, and a tentative timetable was developed. Four
sections were organized, each consisting of scientists from various disciplines. These consultants
prepared drafts that were reviewed by the others and the full Hazardous Materials Advisory Commit-
tee.
Only by the cooperation of many persons was the writing of the report made possible. Mem-
bers of the HMAC who had specific responsibilities were Errett Deck, Leon Golberg and Rosmarie
von Riimker. The coordinators of the respective sections were Phillip Kearney, Chemistry and Anal-
ysis; David Pimentel, Environmental Effects; and Boysie Day, Agricultural and Other Applied Uses.
Leon Golberg, Human Health Effects.
A number of individuals provided advice and assistance in the organization and review of these
four sections and in the preparation of the Committee statement. These included William Ennis,
Donald McCollister, William Upholt, Gordon Guyer, Rosmarie von Riimker, and Errett Deck.
The roster lists the names of those consultants to whom the Committee expresses great appre-
ciation.
Credit is due to the HMAC staff and to Winfred F. Malone for their work on the report.
Emil M. Mrak
Chairman
May 1974
in
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HAZARDOUS MATERIALS ADVISORY
COMMITTEE
Dr. Emil M. Mrak, Chairman
Chancellor Emeritus
University of California
Davis, California
Dr. William J. Darby, Cochairman
President, Nutrition Foundation,
New York, New York, and
Chairman, Department of Biochemistry,
Vanderbilt University
Nashville, Tennessee
Mr. Errett Deck
Chairman, Legislative Committee
Association of American Pesticide
Control Officials
Washington State Department of Agriculture
Olympia, Washington
Dr. Leon Golberg
Scientific Director, Research
Professor of Pathology
Institute of Experimental Pathology
and Toxicology
Albany Medical College
Albany, New York
Dr. Frank Golley
Executive Director and Professor
of Zoology, Institute of Ecology
University of Georgia at Athens
Athens, Georgia
Dr. Gordon E. Guyer
Chairman, Department of Entomology
Michigan State University
East Lansing, Michigan
Mr. Roger P. Hansen
Executive Director
Rocky Mountain Center on Environment
Denver, Colorado
Dr. Paul E. Johnson
Executive Secretary, Food and Nutrition Board
National Academy of Sciences
Washington, D.C.
Dr. Norton Nelson
Director, Institute of Environmental Medicine
New York University Medical Center
New York, New York
Dr. Ruth Patrick
Chairman, Department of Limnology
Academy of Natural Sciences
Philadelphia, Pennsylvania
Dr. William R. Rothenberger
Agricultural Production Specialist
Frankfort, Indiana
Dr. Rosmarie von Riimker
Managing Partner
RVR Consultants
Shawnee Mission, Kansas
Dr. Earl Swanson
Professor of Agricultural Economics
University of Illinois
Urbana, Illinois
Dr. Wilson K. Talley
Assistant Vice President
University of California
Berkeley, California
Dr. W. Leonard Weyl
Chief of Surgery
Northern Virginia Doctors Hospital
McLean, Virginia
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Regular Consultants
Dr. Dale R. Lindsay
Associate Director of Medical and Allied Health
Education
Duke University
Durham, North Carolina
Dr. Caro Luhrs
Medical Advisor to the Secretary
U.S. Department of Agriculture
Washington, D.C.
Dr. Lloyd B. Tepper
Associate Commissioner for Science
Food and Drug Administration
Washington, D.C.
Mr. James G. Terrill, Jr.
Manager, Environmental Consulting
Environmental Systems Department
Westinghouse Electric Company
Pittsburgh, Pennsylvania
Staff
Dr. Winfred F. Malone
Staff Science Advisor
Mrs. Dorothy I. Richards
Administrative Assistant
Mr. W. Wade Talbot
Executive Officer
Miss Jacquelyn A. Cross
Clerk-Typist
VI
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PARTICIPANTS
Grateful acknowledgment is made to the following persons for their contributions in writing
sections of the report and in providing essential guidance:
Committee Statement
Dr. William Ennis
Acting Director, Plant Science Research Division
Plant Industry Station
Agricultural Research Service
U.S. Department of Agriculture
Beltsville, Maryland
Dr. Rosmarie von Ru'mker
Managing Partner
RVR Consultants
Shawnee Mission, Kansas
Mr. Errett Deck
Chairman, Legislative Committee
Association of American Pesticide Control
Officials
Washington State Department of Agriculture
Olympia, Washington
Dr. Winfred F. Malone
Staff Director, Hazardous Materials Advisory
Committee
U.S. Environmental Protection Agency
Washington, D.C.
Chemistry and Analysis
Dr. Philip C. Kearney, Coordinator
Chief, Pesticide Degradation Laboratory
Agricultural Environmental Quality Institute
U.S. Department of Agriculture
Beltsville, Maryland
Dr. George Yip
Chief, Industrial Chemical Contaminants Branch
Division of Chemical Technology
Food and Drug Administration
Washington, D.C.
Environmental Effects
Dr. David Pimentel, Coordinator
Professor, Department of Entomology and
Limnology
New York State College of Agriculture
Cornell University
Ithaca, New York
Mr. Eugene Kenaga
Associate Scientist
Agriculture-Organics Department
Dow Chemical Company
Midland, Michigan
Dr. F. W. Slife
Professor of Weed Science
Department of Agronomy
University of Illinois
Urbana, Illinois
Mr. Harold Mooney
Associate Professor of Biology
Stanford University
Stanford, California
Dr. R. E. Odum
Associate Professor of Forestry
Kansas State University
Manhattan, Kansas
Dr. Lucille Stickel
Pesticide and Pollution Research Coordinator
Patuxent Wildlife Research Center
U.S. Department of the Interior
Laurel, Maryland
vn
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Agricultural and Other Applied Uses
Dr. Boysie E. Day, Coordinator
Director, California Agricultural Experiment
Station
University of California
Berkeley, California
Dr. Arnold Appleby
Farm Crops Department
Oregon State University
Corvallis, Oregon
Mr. Errett Deck
Chairman, Legislative Committee
Association of American Pesticide Control
Officials
Washington State Department of Agriculture
Olympia, Washington
Dr. Stanford Fertig
Director of Research and Development
Agricultural Chemicals Division
Amchem Products, Inc.
Ambler, Pennsylvania
Dr. Peter A. Frank
Department of Agriculture
Denver Federal Center
Denver, Colorado
Mr. William A. Harvey
Botany Department
University of California
Davis, California
Dr. Dayton L. Klingman
Crops Research Division
Plant Industry Station
U.S. Department of Agriculture
Beltsville, Maryland
Dr. Michael Newton
Forest Research Laboratory
Oregon State University
Corvallis, Oregon
Dr. Paul W. Santlemann
Agronomy Department
Oklahoma State University
Stillwater, Oklahoma
Mr. Charles Walker
Chief, Branch of Pest Control Research
Bureau of Sport Fisheries and Wildlife
Division of Fishery Research
U.S. Department of the Interior
Washington, D.C.
Coordinating Members of the Hazardous Materials Advisory Committee
Mr. Errett Deck
Chairman, Legislative Committee
Association of American Pesticide Control
Officials
Washington State Department of Agriculture
Olympia, Washington
Dr. Rosmarie von Riimker
Managing Partner
RVR Consultants
Shawnee Mission, Kansas
Dr. Leon Golberg
Scientific Director, Research
Professor of Pathology
Institute of Experimental Pathology
and Toxicology
Albany Medical College
Albany, New York
vin
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CONTENTS
COMMITTEE STATEMENT 1
Introduction 1
Chemistry 2
Environmental Effects 4
Agricultural and Other Applied Uses 7
CHEMISTRY AND ANALYSIS 11
Findings 11
Chemistry of Herbicides 11
Introduction 11
Basis of Chemical Classification 12
Chemical Properties of Herbicides 18
Contaminants 33
Herbicide Metabolism 34
References 35
Analysis of Herbicides 36
Introduction 36
Current Methodology 37
Current Instrumentation 38
Specificity and Sensitivity Needs 40
Confirmation and Methodology 40
Current Outlook 42
References 43
ENVIRONMENTAL EFFECTS 45
Findings 45
Introduction 47
Sources and Movement of Herbicides in the Environment 48
Residues of Herbicides 56
Bioaccummulation of Residues 56
Residues in Soil 57
Residues in Water 59
Residues in Air 59
Ecological Effects 60
Economic and Ecological Consequences of Alternative Weed-Control Practices 64
Crop Weed Control 64
Industrial Weed Control 68
Aquatic Weed Control 69
References 70
AGRICULTURAL AND OTHER APPLIED USES 75
Findings 75
Forest Management 75
Grazing Lands 75
Aquatic Uses of Herbicides 75
IX
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Herbicides in Crops 76
Industrial Weed Control 76
Forests 77
The Forest as a Resource 77
Unique Features of Forests Under Management 78
The Forest as a Dynamic System 78
History of Forest Exploitation 79
Operating Premises and Management Alternatives 79
Conclusions 92
References 93
Grazing Lands 93
Introduction 93
Methods of Brush Control 97
Methods of Herbaceous Weed Control 101
Brush and Weed Control on Pastures 104
Selected Data Comparing Different Methods of Weed and Brush Control 106
References 110
Aquatic Uses 112
Characteristics and Distribution of Troublesome Aquatic Vegetation 112
Activities and Resources Affected by Aquatic Vegetation 113
Aquatic Vegetation Management With Herbicides 115
Emersed and Marginal Weeds 120
Alternative Methods of Aquatic Vegetation Management 121
Advantages and Disadvantages of Chemical Methods 123
References 134
Crops 136
Introduction 136
Minor Acreage Crops 138
References 139
Row Crops 140
References 150
Fruit and Nut Crops 151
References 153
Solid-Seeded Annual Crops 153
References 155
Solid-Seeded Perennial Crops 155
References 158
Industrial and Urban Sites 158
Utility Rights-of-Way 158
Railroads 164
Industrial Areas 166
Ditch and Canal Banks 167
Domestic and Recreational Uses—Weed Control in Turf 168
Introduction 168
Methods of Weed Control 171
Bibliography 178
Appendix I. STRUCTURE AND PHYSICAL PROPERTIES OF SOME HERBICIDES 180
Appendix II. GLOSSARY 182
Appendix III. COMMON AND CHEMICAL NAMES OF HERBICIDES 186
INDEX 189
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COMMITTEE STATEMENT
INTRODUCTION
This herbicide study was prepared by the Hazardous Materials Advisory Committee in response
to a request from the Administrator of the Environmental Protection Agency. Leading scientists in
the herbicide field contributed to sections on chemistry and analysis, environmental effects, and
agricultural and other applied uses. The purpose of the study is to assess the usage patterns and
benefits of using herbicides and to gain greater knowledge of the environmental effects of these com-
pounds. The discussion covers herbicide use, available alternatives, and approaches to understanding
and solving problems.
A number of herbicides were considered in the analysis, selected partly on the basis of usage.
They included, among others, butylate, Propazine, trifluralin, chloramben, 2,4-D, nitralin, alachlor,
linuron, endothall, diuron, atrazine, and propachlor.
The problems of environmental pollution, including chemical pollution, are the result mainly
of industrialization, urbanization, and intensive agricultural practices. Pesticides of all kinds consti-
tute about 2 percent by weight of the total chemicals used in our society. Herbicides make up about
50 percent of the quantities of pesticides used in the United States. The major concern in the past
was related to the acute toxicity of these various environmental contaminants. More recently con-
cern about possible chronic effects on wildlife, water quality, and other aspects of the environ-
ment has intensified.
The purpose of this report is to assemble available information in these several subject areas,
to describe and evaluate different approaches to solving problems, and to improve our understand-
ing of the subject. It is hoped that this will assist EPA in evaluating risks and benefits when
determining if there is need for regulatory action on a herbicide. This report is a compilation of
the thoughts of many individuals. Thus its strength or weakness depends on the individual views
of its contributors.
Scope
Herbicides are used to control weeds in croplands; to improve the production of desirable
forage in pastures and grazing lands; to control aquatic weeds where they interfere with water use
(irrigation, navigation, recreation, etc.); in forestry, to promote the growth of timber by controlling
unwanted species; industrially, to maintain utility and highway rights-of-way and to eliminate
hazards around oil tanks and railroad tracks; recreationally, to maintain desirable turf on lawns,
on golf courses, and in parks; and to control poisonous and allergenic plants, such as poison ivy and
ragweed, in the interest of the health and well-being of man.
Herbicides are important tools for suppressing unwanted species of plants. They are used
along with cultural practices to provide integrated systems of vegetation management. Although
alternatives to herbicides—such as hoeing, cultivating, and crop rotation—have been used for
generations, herbicides are valuable adjuncts to these traditional and often laborious methods of
controlling weeds. Herbicide use does not substitute for good management practices in farm and
ranch operations or in other habitats where weeds need controlling. Herbicide use involves both
benefits and risks, which need to be evaluated.
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Extent of Use
Current estimates suggest that about 134 herbicides are registered in the United States.
Products formulated from these chemicals number in the thousands. In 1970 approximately 391
million pounds of organic herbicides were synthesized domestically. As a specific example, the
USDA Pesticide Review, 1971, published in March 1972, lists domestic production of 2,4-D in
1970 at 43.5 million pounds. There are 21 herbicides registered for corn, the top two being
atrazine and 2,4-D. Data from a survey conducted by the U.S. Department of Agriculture
indicate that 76 percent of the 64.3 million acres of corn harvested in 1968 were treated for
weed control. Comparable figures for other crops in 1968 are as follows: soybeans, 40.6 million
acres, 22 million treated; cotton, 10.1 and 9 million; wheat, 55.3 and 21.2 million. Most field
crop rates of application in accordance with EPA-registered herbicide labeling vary from 0.25 to
4 pounds per acre.
In the United States during 1970 nearly 1 billion pounds of pesticides (about 50 percent
herbicides) were used to control about 2000 pest species, or about 1 percent of the total species.
In the process, many nontarget species in the environmental life system are directly or indirectly
affected by the use of insecticides, fungicides, herbicides, and other pesticides.
CHEMISTRY
Major Classes of Herbicides
Each currently used herbicide can be categorized on the basis of its chemical structure. The
number of groups can vary from 10 to 25, depending on the refinement of the categories. A few
exceptions would fall into a miscellaneous group. A suggested classification is shown in Table 1.
Use of Classification Scheme
A proposed new herbicide may be identified with a class based on its chemical structure.
Potential problems are associated with various classes. Tests based on prior experience can be
conducted early in the research phases to identify compounds that may have potential environ-
mental or health-related effects.
An example of how the above classification system can be used in a decision-making process is
illustrated. The detection of TCDD, a dioxin (specifically 2,3,7,8-tetrachlorodibenzo-p-dioxin),
in 2,4,5-T raised the question whether TCDD might be present in other herbicides. The formation
of TCDD occurs in the manufacturing process during the production of trichlorophenol. Therefore
it would be logical to examine herbicides in groups I and IX (see Table 1) for dioxin contaminants.
Since TCDD formation requires high-temperature hydrolysis and a chlorine atom in the 2-position
on the ring, certain herbicides from groups I and IX would not be suspect. The phenol in 2,4-D and
related dichlorophenoxy herbicides is prepared by chlorination (i.e., no elevated temperatures are
involved); hence herbicides manufactured as such could be disregarded in group I. By this process
of elimination, certain herbicides remain suspect for dioxin content. Investigators have analyzed
approximately 129 samples of 17 different phenol-based pesticides for TCDD content; no dioxins
were detected in 76 percent of the samples analyzed.
As environmental and health-effects issues are raised about various herbicides—such as
impurities (e.g., dioxins) or metabolites—the chemical classification system becomes a valuable
tool for selecting chemically related herbicides for examination and testing.
Compounds Under Consideration
Some of the major herbicides evaluated in this report with reference to their possible environ-
mental effects are listed in Table 2. Of the 15 herbicides listed, there is a close chemical relation-
ship between alachlor and propachlor, linuron and diuron, atrazine and Propazine, and trifluralin
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Table 1. MAJOR CHEMICAL CLASSES OF HERBICIDES
Group Chemical class Examples
I Chlorinated phenoxyalkanoic acids 2,4-D, 2,4,5-T, Silvex
II s-Triazines Atrazine, Propazine, simazine
III Phenylureas Fenuron, linuron
IV Carbamates Barban
V Thiocarbamates Butylate
VI Amides Alachlor, propachlor
VII Chlorinated aliphatic acids Dalapon
VIII Chlorinated benzoic acids Chloramben, dichlobenil
IX Phenols Bromoxynil, DNOC
X Substituted dinitroanilines Nitralin, trifluralin
XI Bipyridiniums Diquat, paraquat
XII Arsenicals Cacodylie acid
XIII Uracil derivatives Bromacil, terbacil
Miscellaneous Acrolein, endothall, picloram
Table 2. HERBICIDES REVIEWED IN DETAIL IN THIS REPORT
Common name Chemical name
Alachlor1 2-Chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide
Propachlor1 2-Chloro-N-isopropylacetanilide
Linuron1 3-(3,4-Dichlorophenyl)-1-methoxy-1-methylurea
Diuron1'2 3-(3,4-Dichtorophenyl)-1,1-dimethylurea
Atrazine1 2-Chloro-4-ethylamino-6-isopropylamino-s-triazine
Propazine1 2-Chloro-4,6-bis(isopropylamino)-s-triazine
Trifluralin1 a,a,a-Trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine
Nitralin1 4-(Methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline
2,4-D (2,4-Dichlorophenoxy)acetic acid, its amine salts and esters
Chloramben 3-Amino-2,5-dichlorobenzoic acid
Butylate S-Ethyl diisobutylthiocarbamate
Miscellaneous:
Acrolein2 2-Propenal
Copper sulfate2
Endothall2 7-Oxabicyclo(2,2,1)heptane-2,3-dicarboxylic acid
Xylene2
'Compounds chemically related: alachlor and propachlor, linuron and diuron,
atrazine and Propazine, and trifluralin and nitralin.
2Compounds of interest because of sites of application (aquatic).
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and nitralin. Some of the products listed are of interest mainly because of the aquatic sites of
application. Their importance is thus principally related to their potential environmental impact.
ENVIRONMENTAL EFFECTS
Herbicides constitute an important management tool whose intended effects in plant control
represent a significant environmental impact that is beneficial in the control of weeds but in some
cases adversely affects nontarget organisms. The environmental effects on soil, water, and air,
together with the impact on life systems, are discussed in this section.
Sources and Movement
The occurrence of herbicide residues in both target and nontarget areas and their effects
depend on (1) persistence, (2) amount used, (3) application method, (4) movement, (5) toxicity,
and (6) possible bioconcentration. Although pesticides exhibit a wide range in toxicity to
animals, herbicides as a class are generally less toxic than insecticides. The accumulation of
certain herbicides does occur in plants, and this can be a hazard. The chances of a herbicide
becoming a hazard are greater if it is persistent.
Bioaccumulation of Residues
Use of the terms "bioaccumulation" and "bioconcentration" may conjure up the image of the
type of residue accumulation that occurs with the insecticide DDT in the fat tissues of animal
organisms. The bioconcentration factor (bioaccumulation) is the ratio of the measured residues in
animal or plant (or specific tissues thereof) compared to the residues of the pesticide in the ambient
air, water, or soil environment of the organism and/or the various species of food organisms con-
sumed, as specified. The highest bioconcentration factors in animals usually occur in water with
chlorinated insecticides; for example, DDT and its metabolite DDE may have a bioconcentration
factor of 106. Such herbicides as picloram, Silvex, 2,4-D, and dichlobenil appear to bioconcentrate
as much as tenfold in fish or other aquatic organisms but not at all in other species. Diuron may
have a bioconcentration factor of several hundred. These herbicides degrade in both plant and soil
systems.
Data on herbicide residues in wild mammals and birds are scarce. However, domestic animal
and bird tissues appear to be free of residues that would be significant for human use.
The terms "bioaccumulation" and "bioconcentration" may be applied to plants. The prop-
erties of a chemical used to penetrate and kill insects are generally quite different from those
needed to penetrate and kill plants. Insecticides that are nonsystemic poisons are often quite
soluble in fats (in order to penetrate insects) but fairly insoluble in water; thus stable compounds
may be bioaccumulated in animal fats and be consumed by other animals. Many herbicides are
water soluble and do not partition as greatly in favor of fat tissues as do organochlorine insecticides.
Degradation of most herbicides leads to more polar products. Many herbicides are systemic, that
is, they penetrate plants and thus redistribute residues, especially in the growing portions of the
plants, such as leaves and roots. Although many herbicides are rapidly metabolized to nontoxic
compounds in plant tissues, some herbicide residues persist at detectable levels.
Residues in Soil
A major problem in assaying herbicide soil residues is the accurate measurement of actual
amounts of the compound and/or its degradation products in varying time periods after application.
Only a few studies include a wide variety of the most commonly used herbicides tested comparatively
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in the field. A Southern States Regional Cooperative Study showed that no phytotoxic residues of
atrazine, diuron, linuron, or trifluralin persist in soil after 1 year when the herbicides are applied at
recommended rates. However, no analytical data were included on nonphytotoxic residues that
might have been present.
Herbicide residues are likely to persist longer in the colder areas of the United States and
Canada. An example is the carryover of phytotoxic levels of atrazine from the year of application
to the next year, which has caused damage to susceptible crops such as beans. In Oregon, studies
of chemical brush control with several compounds indicated that detectable residues of picloram
persisted for more than a year while the others degraded more rapidly. Herbicide persistence is
affected by many variables, including concentration, temperature, moisture, pH, soil type, microbial
ecology, formulation, and chemical structure.
Residues in Water.—The most common herbicides used to control aquatic weeds are xylene,
copper sulfate, 2,4-D, acrolein, endothall, dichlobenil, and diquat. Few materials are registered
for this use because of potential access to potable water supplies and potential environmental
problems.
The main potential sources of herbicidal residues in water are direct application, drift from
aerial application, runoff from treated land, treatment of ditchbank vegetation, and faulty waste
disposal techniques by the manufacturer, homeowner, commercial applicator, or farmer.
Limited pesticide residue monitoring studies have been conducted by various U.S. agencies.
Very low levels of residues were found in a few samples, but none were biologically significant
in the waters monitored. Herbicide (2,4-D) residues in bottom muds of cold lakes or those with
a low oxygen content may persist for months. Eleven streams in the western United States were
monitored for 2,4-D, 2,4,5-T, and Silvex. No herbicide residues were found.
A number of chemicals that are persistent in soils are less persistent in water due to the
action of ultraviolet light. A herbicide like picloram, which is resistant to degradation in soil,
is more easily decomposed by sunlight in surface water, with a half-life ranging from 2 to 41
days, depending on water depth, amount of sunlight, and water quality. More studies on various
herbicides concerning decomposition by sunlight are needed to help calculation of their half-life
in water.
Residues in Air.—Herbicide residues in air come principally from three sources: (1) spray-
particle drift at the time of application; (2) dispersal of herbicides on particles due to wind erosion
after application; and (3) gaseous dispersion because of volatility at the time of application or from
soil, water, plants, or other treated areas. Items 1 and 3 are most important.
Occasionally, during periods of great wind storms, the accompanying dust storms may
deposit small but detectable residues of herbicides—presumably carried over great distances
(such as from Texas to Ohio) on contaminated or treated soil particles. Even during normal weather,
particulate matter suspended in air may absorb volatile herbicides and then be redeposited on bodies
of water or on the ground by rain storms some distance from the original source of the application.
Particles from air have been shown to contain 2,4,5-T in amounts of up to 0.04 ppm.
Drift of fine aerosol spray particles and 2,4-D vapors from volatile formulations may be
responsible for considerable damage to sensitive nontarget plants surrounding target areas. The
presence in air samples of various salts and esters of 2,4-D has been studied in the state of
Washington. The volatility of 2,4-D formulations varies greatly from the high-volatile esters to
the low-volatile esters and the relatively nonvolatile amine salts. Investigations of crop damage
have verified that volatility is a major contributor to 2,4-D drift damage.
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The volatility of a given herbicide from various treated surfaces varies greatly, depending on
the weather, formulation, and adsorptive capacity of the surface from which the herbicide volatilizes.
Generally speaking, soil and other surfaces that adsorb herbicides to the greatest extent allow the
least volatility. A large percentage of certain herbicides can be lost within a few hours or days by
volatility unless incorporated with the soil.
Impact on Life Systems
The desired effect of herbicides is to kill weeds, retard their growth, or selectively alter the
plant cover. Associated with herbicide use are other ecological effects—some beneficial and some
harmful.
Although herbicides are intended to control unwanted plants, their effects are not limited to
plants. Some animal species are quite susceptible to the direct action of these compounds. The
mammal and bird species tested were relatively tolerant to herbicides, but fish and invertebrates
were relatively susceptible to some compounds, such as trifluralin and dichlone. The hazard of
such herbicides is important and must be carefully evaluated. When emulsified in water, trifluralin
kills fish at very low concentrations. When applied to soil, it is strongly absorbed by the soil and
presents little risk of water contamination.
Herbicides may affect nontarget organisms within a target area, such as the microorganisms that
are important in nitrification and in degrading wastes. However, the current use patterns of herbi-
cides as well as laboratory and field data suggest that herbicides do not constitute a serious threat to
the microbial equilibrium of the soil.
Herbicides may reduce or eliminate natural resistance in plants, rendering them more suscepti-
ble to attack by pests. For example, red clover and oat strains resistant to pest nematodes lost their
resistance when exposed to low levels of 2,4-D.
Herbicides may alter the nutritional content of crops—either increasing or decreasing their
food value. The protein content of oats, for instance, was increased with simazine by 28 percent
over that of untreated oats. However, beans grown as a second crop on previously treated soil were
observed to have a lower level of protein than a control. The carotene content of carrots was in-
creased after treatment with linuron.
Under certain conditions, insect pests and plant pathogens have been found to increase after
using herbicides. Although the examples given are relatively isolated and the relationships not
fully understood, they indicate the desirability of more in-depth follow-up studies. Apparently
some weed killers alter the chemical makeup of the crop plants, making them more susceptible to
insects, which consequently become more abundant on the treated crop plants. For example,
higher than recommended 2,4-D applications resulted in increased wireworm damage to wheat.
In one report the number of grasshoppers on pasture plots treated with 2,4-D was approximately
double that on check plots. It was not determined whether the increase resulted from nutrition or
a change in plants or plant populations. Bean plants exposed to sublethal levels of 2,4-D increased
aphid progeny production during a 10-day period from 139 to 764 per aphid. Rice stalk borer
larvae grew nearly twice as large when larvae were fed rice treated with 2,4-D. Even so, 2,4-D has
been used extensively for over 25 years without significant impact on nonweed crop pests.
In addition, insect pests may increase if the number of beneficial insect predators is reduced
after using herbicides. Aphid infestations were reported on oats after the use of 2,4-D because
fewer predaceous coccinellid beetles were present and active in the crop. The occasional adverse
effects on beneficial insects are probably associated with the destruction of weed habitat.
-------
Few quantitative studies have been made to ascertain the indirect effects of herbicides on the
population sizes of nontarget organisms in a system. However, because of actual animal and plant
interrelationships, we would expect the population sizes of nontarget species to be either increased
or decreased after herbicide treatments. Some bird-population reductions may be attributed in
part to the elimination of shrubby roadside habitats by herbicides. On the other hand, deer popula-
tions in some areas were increased by herbicide use. Unintentional responses reported have not been
of such economic or ecological importance as to significantly affect the benefit-to-risk ratio of most
established uses.
Pond ecology and production can be affected by herbicide use. For example, simazine applied
experimentally to ponds controlled the weed Potamogeton foliosus and all filamentous forms of
algae for almost 5 months. It also lowered the pH of the water and drastically changed the species
composition of bottom-dwelling invertebrates. Residues persisted for at least a year. A number of
herbicides, such as the sodium salt of dalapon, diquat, and the dipotassium and disodium salts of
endothall, have shown a safe margin for toxicity to fish and fish-food organisms.
AGRICULTURAL AND OTHER APPLIED USES
In this section, the use for herbicides in forestry, orchards, small fruits, grazing lands, crops,
industrial rights-of-way, and aquatic situations will be briefly summarized.
Forestry
Herbicides are one of many management tools available for improving or maintaining yields
from commercial forest lands. The management of forests is an economic necessity. Cutting
commercial trees leaves undesirable species that may remain dominant thereafter. The use of
least disturbing practices tends to promote forest stability with minimum loss from erosion and
nutrient leakage.
Herbicides provide one of the most selective methods of eliminating shrub or cull-tree species
to enhance desirable forest growth. The beneficial effect of a herbicide is greater and more perma-
nent than the effective life of the chemical residues. The effects on wildlife habitat—desirable or
otherwise—depend on the original habitat condition.
In forestry, herbicides are generally applied from aircraft. Unless proper and rigid precautions
are followed, it is difficult to control the subsequent movement of herbicides, and drift can seriously
damage susceptible nontarget vegetation. Thus great care must be exercised to (1) use proper
formulations; (2) leave unsprayed strips and buffer zones around streams and other water areas,
susceptible crops, and populated areas; (3) avoid application immediately before a heavy rainfall;
(4) avoid spraying when there is excessive wind or an atmospheric inversion; (5) use coarse sprays;
and (6) fly as low as practical.
Grazing Lands
The primary purpose of weed and brush control is to change the predominant vegetative
composition of the grazing site from undesirable to desirable species. Aerial spraying is an
important means of application on the more extensively brush-infested ranges and pastures.
Because of the selectivity and slow action of some herbicides, the species of plants that are not
killed increase in size and cover coincident with the death of unwanted species. Thus soil protection
may be more continuous than with some alternatives like bulldozing, which leaves the land suscepti-
ble to erosion. Alternative mechanical methods are relatively nonselective, and affected areas
-------
usually must be reseeded. This reseeding may not always be successful because of lack of soil
stability or shade from prior cover.
Brush control on grazing land results in more than just increased forage production. Addi-
tional benefits may include a reduction in the cost of caring for livestock, ease of livestock produc-
tion, reduced wind and water erosion, and more groundwater production in some situations over a
longer period of time.
Most residues resulting from herbicides used on grazing lands have relatively short persistence
(1 to 12 months) in soils and dissipate rapidly from animal tissues.
Aquatic Situations
Although aquatic vegetation is essential to the aquatic environment, excessively large popula-
tions or masses of aquatic plants may become highly detrimental to other aquatic organisms and re-
duce the usefulness of water for many other purposes. In the Western States aquatic weeds are a
problem in over 100,000 miles of irrigation canals, reducing water flow, plugging up equipment,
and resulting in a serious loss of water. The control of undesirable aquatic vegetation is also essen-
tial in wildlife and fisheries management. In the inland waterways of the Southeastern United
States aquatic plants interfere with navigation. There are few alternatives to the use of aquatic
herbicides, and these alternatives may incur greater environmental risk than herbicide use.
Because the aquatic environment is complex and misuse of chemicals could be far reaching,
users of aquatic herbicides should have adequate training and experience. Many states are now
employing a permit system of use. Permits are issued locally by professional agriculturists, wildlife
specialists, or other trained experts who have experience in the field. The application of herbicides
in public waters should be limited to trained commercial applicators or qualified state employees.
Field and Vegetable Crops
Herbicides used on field crops account for 84 percent of all herbicides used in agriculture.
Atrazine is the most widely used herbicide, and corn receives more herbicides (over 40 percent)
than any other crop. Depending on weather, weed species, soils, and cropping systems for corn,
either herbicidal control, mechanical control, or a combination of these practices may be more
effective. For example, under wet conditions herbicides may be more effective than mechanical
cultivation; but under dry conditions mechanical control may be more effective than herbicides.
Unfortunately, we cannot predetermine these weather conditions. A combination of controls for
weeds leads to increased use of early planted corn that utilizes the full growing season, and thus
increases yields. Planting in the Corn Belt about May 1 with the long-growing varieties means that
field conditions are normally wet and cool, and hence herbicidal weed control is needed in early
spring.
Chemical weed control diminishes restraints on crop rotations and disturbance of soil; it
allows adjustment of row spacing to that optimum for each crop and the use of mechanical
harvesting; it also results in economy of labor. Both yields and quality are improved through
reduced competition from weeds, and usually costs per unit of production are lowered. For
example, in the last decade the amount of hoe labor for cotton production in certain areas of the
United States was reduced from 48 to 13 man-hours per acre by the use of herbicides. The cost of
labor for weeding strawberries decreased from as much as $200 to as little as $16 per acre where
selective herbicides were used in combination with cultivation. Eliminating herbicide use in the
absence of feasible alternatives would eliminate the economic production of small grains in much
of the Pacific Northwest. Weeds would severely compete for limited moisture and plant food, and
-------
would interfere with harvest operations. In a North Dakota study it was found that an estimated
annual loss of $175,000,000 would result from discontinuing the Use of 2,4-D and MCPA in cereal
grains and flax. These herbicides are the only feasible method now available for controlling wild
mustard.
Depending on the weather, weeds, and labor availability, net economic returns may be highest
in corn production employing herbicides, mechanical cultivation, or a combination for weed con-
trol. Weed-control costs in corn employing herbicides where two herbicides are used range from
$10 to $14 per acre, whereas the cost of three mechanical cultivations may range from $4 to $6
per acre. Usually a combination of herbicides and mechanical cultivations results in higher corn
yields than those obtained by either method alone, and net returns are also higher. In the Corn
Belt, higher soybean yields were obtained using a combination of herbicides and cultivation than
with cultivation alone.
Fruit and Nut Crops
The cost of hand labor to control unwanted vegetation has become almost prohibitive on a
commercial scale. Mowing, tillage, and the use of herbicides in various combinations are currently
used to eliminate weeds as competition and as secondary hosts for other pests. Control is particu-
larly critical in establishing a new orchard. Increased growth and yields result from the use of
herbicides as compared with the use of mechanical weed-control techniques alone. Some of these
benefits result from less competition for water and nutrients and from rodent and insect control.
Industrial and Domestic Weed Control
Nonchemical weed-control methods like mowing are helpful at some industrial sites, but
herbicides are best suited to most industrial situations. Vegetation is controlled to minimize fire
hazard, prevent interference with the transmission of essential public utilities, permit right-of-way
maintenance, improve ballast drainage, and ensure roadside visibility. Among the factors to con-
sider when selecting the method or combination of methods employed are accessibility (including
type of terrain), erosion potential, possible effects on animal life, relationship to water supplies,
potential drift to nontarget plants, and economics.
Turf, the preferred cover in many industrial as well as home and recreational situations, is
difficult to maintain satisfactorily by cultural means alone.
Benefits and Risks
The assessment of the benefits and risks entailed in the use of herbicides or any other similar
agricultural management tool is highly complex. Since both an ample food supply and a viable
agricultural environmental life system are necessary for human survival, man must carefully manage
his environment to ensure adequate food production. Herbicides are management tools that bring
about significant, intended environmental effects; however, any unintentional health or ecological
risk should be examined.
No single factor accounts for the high productivity of farmlands in the United States. Cultural
practices, fertilizers, varieties that are high yielding and disease resistant, and control of insect pests
and weeds all contribute. In terms of modern agriculture and forestry, a major benefit from the use
of herbicides is the decreased labor, power, and machinery costs for weed control. The ability to
effectively control weeds in a timely manner increases the quality and yield of marketable crops.
Hand labor for many crops is almost eliminated, and the released labor can be diverted to other
productive work activities.
-------
In making assessments, each particular weed-control situation must be evaluated on the basis
of the best available knowledge of the economic, environmental, and health benefits and risks.
This study presents evidence that (1) herbicide use increases the yield of many crops (in addition to
this obvious food-production benefit, some land is released from cropping, which is a beneficial
environmental impact); (2) herbicides used to control aquatic weeds may improve some lakes and
pond environments used for recreation; and (3) herbicides have been effectively used in some cases
to improve habitats.
As mentioned, associated with the intentional benefits of herbicide use are certain environ-
mental risks:
1. Herbicide carryover residues have resulted in phytotoxic effects on susceptible plants, but
generally residues do not seem to be building up in the air, water, and soil environment. Monitoring
should be continued, however.
2. Herbicides in some instances may alter nutritive constituents of plants, such as proteins,
vitamins, and related materials, but these changes have not resulted in significant effects on yield or
quality of crops.
3. In limited experiments, nontarget plants and other organisms have been shown to be affected
by herbicide exposure; therefore field experiments should be continued and expanded.
4. Based on minimal data, herbicide impact on natural ecosystems appears to be minor.
Weeds can be controlled by herbicides, by mechanical cultivation, by hand labor, or by a com-
bination of practices. Which alternative is most efficacious depends on a spectrum of interacting
variables for each particular situation, including crop rotation, soil, weather, weed species, terrain,
and economics. Each weed-control situation should be evaluated on the basis of the best available
knowledge of the benefits and risks to humans and the environment.
10
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CHEMISTRY AND ANALYSIS
FINDINGS
1. Currently used herbicides can be placed in one of 13 well-defined groups on the basis of
chemical structure, with a few exceptions that fall into a miscellaneous group.
2. Proposed new herbicides can therefore be grouped, and one can be alerted to possible haz-
ards associated with the group in question.
3. Tests applicable for groups in question should be conducted to prove or disprove the
existence of problems.
4. Monitoring of herbicides should be continued to minimize the danger of contamination.
5. Nearly all herbicides are at least partially metabolized by some plant, animal, or soil-
microbial system.
6. The factors that render many herbicides biodegradable are poorly understood.
CHEMISTRY OF HERBICIDES
Introduction
Large-scale weed control by chemicals is a relatively recent development in agriculture. Prior
to the 1940s, which is generally considered the beginning of the modem era of chemical weed control,
certain inorganic salts were used as herbicides. In biblical times such herbicides as ashes, common
salts, and bittern were used in agriculture. Due to the nonselective nature of these materials, one
suspects that they were used sparingly for localized treatment and that cultivation was the major
method of weed control.
An interesting history of weed control prior to the introduction of chemical herbicides has been
prepared by Timmons (1970). The first selective action of an inorganic salt was demonstrated by
Bonnet (1897) in France in 1896, who showed that copper sulfate controlled charlock [Brassica
kaber (B.C.) L. C. Wheeler] in wheat. Many inorganic salts have been tried as herbicides including
such compounds as ammonium thiocyanate (NH4SCN), ammonium nitrate (NH4NO3), ammonium
sulfate [(NH4)2SO4], ferrous sulfate (FeSO4), and copper sulfate (CuSO4). The most widely used
inorganic herbicides, however, were arsenate, borate, and chlorate, usually as the sodium salts. The
two valence states of arsenic in pesticides are the trivalent form (As3+), as in sodium arsenite, and
the pentavalent form (As5+), as in sodium arsenate.
Sodium arsenite has been widely used since about 1890 as a weed killer, particularly as a non-
selective soil sterilant. Consequently, it found use around military and commercial installations
along roadsides and on railroad rights-of-way. Since about 1925 sodium arsenite has been used
rather extensively as an aquatic herbicide in lakes and farm ponds. From 1902 to 1937 it was used
11
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by the U.S. Army Corp of Engineers for controlling waterhyacinth in Louisiana. The use of sodium
arsenite for controlling crabgrass (Digstaria samquinalu) expanded rapidly from only a few hundred
tons in the early 1950s to 5000 tons in 1959, or about 17 percent of the total arsenic consumption
in the United States that year. Due to its highly toxic nature (LD50 = 10 nig/kg), sodium arsenite
has largely been displaced by the organic herbicides.
Borates are generally used for nonselective long-term weed control, in combination with other
herbicides such as 2,4-D, TCA, ureas, and triazines. Sodium chlorate, like the borates, is used pri-
marily as a soil sterilant and is applied at rates of 200 to 1000 Ib/acre. It was first used for weed
control in France in 1923 and in the United States from 1925 to 1930. Despite its rather high cost
and serious fire hazard, its use expanded rapidly. Idaho used 4 million pounds from 1927 to 1935,
and Kansas used nearly 3 million pounds from 1939 to 1940 (Timmons, 1970).
Tvv'o other inorganic herbicides of some significance are ammonium sulfamate and sulfuric acid.
Ammonium sulfamate (NH4SO3NH2) is a highly water soluble compound of low mammalian toxic-
ity and has been used primarily for brush control since about 1940. Sulfuric acid (H2SO4) has been
used since the turn of the century for controlling annual weeds. It was first used by the French for
the control of annual forbs in cereals in 1911. By 1935 sulfuric acid was being used in the United
States for weed control in onions (Allium cepa L.) and to some extent in cereals. Due to its corro-
sive nature, the use of sulfuric acid as a herbicide declined with the introduction of selective organic
compounds.
Although the modern era of organic chemicals used as herbicides is generally attributed to the
development of 2,4-D in the early 1940s, there are several examples of earlier successes with syn-
thetic organic herbicides. Kogl et al. 's discovery in 1934 that indoleacetic acids promoted cell
elongation in plants led to the synthesis and evaluation of many structurally related organic com-
pounds. Two years prior to this discovery, 3,5-dinitro-o-cresol was introduced as a herbicide for
weed control. Dinitrocresol (DNOC) had been used as an insecticide since 1928, but in 1932 the
selective herbicidal action of this and related compounds was discovered. The discovery of the
phenoxyalkanoic acid herbicides by Zimmerman and Hitchcock at the Boyce Thompson Institute
in 1942 ushered in an era of tremendous growth of synthetic organic herbicides.
The phenomenal growth of the herbicide industry occurred primarily after 1950. By 1950
the number of herbicides available for public use had increased to about 25 from the 15 available
in 1940. The subsequent growth and chronology of new herbicides since 1950 has been summarized
by Timmons (1970) and is given in Table 1.
In recent years the introduction of new herbicides has been somewhat slowed due to the in-
creasingly stringent requirements for additional information for" registration. The best current esti-
mates suggest that about 163 herbicides are registered in the United States. In 1970 approximately
391 million pounds of synthetic organic herbicides were produced domestically. This accounts for
about 36 percent of all pesticides produced in the United States. Herbicide production grew at an
average rate of 17 percent a year during the 5 years previous to 1970, compared to 8.7 percent for
all pesticides. The formulated products in which these approximately 160 chemicals are utilized
number in the thousands. For this reason, the common names of these 160 or more herbicides are
used in the scientific literature.
Basis of Chemical Classification
The first prerequisite for a decision-making document is a classification system by which all
the components can be analyzed. Herbicides may be grouped by various classification systems, such
as those based on use patterns, time of application, crop selectivity, target plant, or chemical family.
To the chemist the last classification represents the most logical and simplest system for grouping
herbicides.
12
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Table 1. CHRONOLOGY OF NEW HERBICIDES SINCE 19501
Common name
Monuron
Endothal!
Metham
MH
Dalapon
Diuron
Silvex
Amitrole
Erbon
Naptalam
CDAA
Chlorpropham
DSMA
Monuron TCA
Sesone
2,3,6-TBA
CDEC
Dazomet
EPTC
HCA
Neburon
PBA
Fenuron
Simazine
2,4-DB
Atrazine
DCPA
Fenuron TCA
Pebulate
Prometone
Vernolate
Acrolein
Amiben
Dial late
Endothall2
Fenac
2,4-DEP
Amitrole-T
Barban
Cacodylic acid
Propanil
Propazine
Bensulide
Dicamba
Dichlobenil
Diquat
Chemical name
3-(p-Chlorophenyl)-1,1-dimethylurea
7-Oxabicyclo[2.2.1] heptane-2,3-dicarboxylic acid
Sodium methyldithiocarbamate
1 ,2-Dihydro-3,6-pyridazinedione
2,2-Dichloropropionic acid
3-(3,4-Dichlorophenyl)-1,1-dimethylurea
2-(2,4,5-Trichlorophenoxy) propionic acid
3-amino-s-triazole
2-(214,5-Trichlorophenoxy>ethyl 2,2-dichloropropionate
/V-1-Naphthylphtalamic acid
/V,/V-Diallyl-2-chloroacetamide
Isopropyl-m-chlorocarbafiilate
Disodium methanearsonate
3-(p-Chlorophenyl)-1,1-dimethylurea mono
(trichloroacetate)
2-(2,4-Dichlorophenoxy)ethyl sodium sulfate
2,3,6-Trichlorobenzoic acid
2-Chloroallyl diethyldithiocarbamate
Tetrahydro-3,5-dimethyl-2W-1,3,5-thiadiazine-2-thione
S-Ethyl dipropylthiocarbamate
1,1,1 ,3,3,3-H exach loro-2-propanone
1-Butyl-3-(3,4-dichlorophenyl)-1-methylurea
Chlorinated benzoic acid
1,1-Dimethyl-3-phenylurea
2-Chloro-4,6-bis(ethylamino)TS-triazine
4-(2,4-Dichlorophenoxy) butyric acid
2-Chloro-4-ethylamino-6-isopropylaminotf-triazine
Dimethyl tetrachloroterephthalate
1 ,1 -Dimethyl-3-phenylurea monotrichloroacetate
S-Propyl butylethylthiocarbamate
2,4-Bis(isopropylamino)-6-methoxy-s-triazine
S-Propyl dipropylthiocarbamate
acrolein
3-Amino-2,5-dichlorobenzoic acid
S-(2,3-Dichloroallyl) diisopropylthiocarbamate
7-Oxabicyclo [2.2.1 ] heptane-2,3-dicarboxylic acid
(2,3,6-Trichlorophenyl)acetic acid
Tris[2-(2,4-dichlorophenoxy)ethyl] phosphite
3-Amino-s-triazole + ammonium thiocyanate
4-Chloro-2-butynylm-chlorocarbanilate
Hydroxydimethylarsine oxide
3',4'-Dichloropropionanilide
2-Chloro-4,6-bis(isopropylamino)-s-triazine
0,O-Diisopropyl phosphorodithioateS-ester with
A/-(2-mercaptoethyl)benzenesulfonamide
3,6-Dichloro-o-anisic acid
2,6-Dichlorobenzonitrile
6,7-Dihydrodipyrido[1,2-a:2',l'-c] pyrazinediium salts
Year of
first
public use
1952
1953
1953
1953
1954
1954
1954
1955
1955
1955
1956
1956
1956
1956
1956
1956
1957
1957
1957
1957
1957
1957
1958
1958
1958
1959
1959
1959
1959
1959
1959
1960
1960
1960
1960
1960
1960
1961
1961
1961
1961
1961
1962
1962
1962
1962
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Table 1. CHRONOLOGY OF NEW HERBICIDES SINCE 19501-Continued
Common name
Isocil
Linuron
Molinate
—
Triallate
Bromacil
Butylate
Diphenamid
MSMA
Picloram
Trifluralin
Ametryne
Cycloate
loxynil
Prometryne
Siduron
Bromoxynil
Fluometuron
Lenacil
Propachlor
Pyrazon
Benefin
Chloroxuron
Nitrofen
Paraquat
Terbacil
Metobromuron
Nitralin
Karbutilate
Terbutryn
Chemical name
5-Bromo-3-isopropyl-6-methyluracil
3-(3,4-Dichlorophenyl)-1-methoxy-1-methylurea
S-Ethyl hexahydro-1W-azepine-1-carbothioate
Polychlorodicyclopentadiene isomers
S-(2,3,3-Trichloroallyl) diisopropylthiocarbamate
5-Bromo-3-sec-butyl-6-methyluracil
S-Ethyl diisobutylthiocarbamate
/V,/V-Dimethyl-2,2-diphenylacetamide
Monosodium methanearsonate
4-Amino-3,5,6-trichloropicolinic acid
a,a,a-Trifluoro-2,6-dinitro-/\/,/V-dipropyl-p-toluidine
2-(Ethylamino)-4-(isopropylamino)-6-(methylthio)-s-
triazine
S-Ethyl N-ethylthiocyclohexanecarbamate
4-Hydroxy-3,5-diiodobenzonitrile
2,4-Bis(isopropylamino)-6-(methylthio)-s-triazine
1-(2-Methylcyclohexyl)-3-phenylurea
3,5-Dibromo-4-hydroxybenzonitrile
1,1-Dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea
3-Cyclohexyl-6,7-dihydro-1W-cyclopenta-
pyrimidine-2,4(3W,5W)-dione
2-Chloro-/V-isopropylacetanilide
5-Amino-4-chloro-2-phenyl-3(2W)-pyridazinone
/V-Butyl-/V-ethyl-0,a,a-trifluoro-2,6-dinitroiO-toluidine
3-(p-(p-Chlorophenoxy)phenyl] -1 ,1-dimethylurea
2,4-Dichlorophenyl p-nitrophenyl ether
1,l'-Dimethyl-4,4'-bipyridinium salts
3-ferf-Butyl-5-chloro-6-methyluracil
3-(p-Bromophenyl)-1-methoxy-1-methylurea
4-(Methylsulfonyl)-2,6-dinitro-/V,/V-dipropylaniline
m-(3,3-Dimethylureido)phenyl-te/t-butylcarbarnate
2-feAt-Butylamino-4-ethylamino-6-rnethylthio-s-triazine
Year of
first
public use
1962
1962
1962
1962
1962
1963
1963
1963
1963
1963
1963
1964
1964
1964
1964
1964
1965
1965
1965
1965
1965
1966
1966
1966
1966
1966
1967
1967
1968
1969
1 From Timmons (1970). See WSSA Handbook for current chemical nomenclature.
2 For control of aquatic weeds.
In any decision-making process it is important to understand the basis for chemical classifica-
tion and inferences that can be drawn due to similarities in chemical, physical, and biological
properties. These similarities include starting materials, routes of synthesis, impurities, derivatives,
methods of analysis, solubilities, persistence, mobilities, metabolites, and modes of action. A more
detailed analysis of the chemistry of herbicides, particularly individual compounds in large families,
will show certain dissimilarities. It is important to understand how these variations arise and the
chemical basis for these dissimilarities.
Unfortunately, a few herbicides cannot be logically included in any chemical classification
system. These include individual compounds like acrolein, amitrole, endothall, pyrazon, and
14
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picloram. An excellent source of information on the chemical, physical, and biological properties
of many herbicides in current use is the Herbicide Handbook (1974) published by the Weed Science
Society of America.
A classification of herbicides into 13 major groups is found in Table 2. This table is not all-
inclusive, but is designed to group those compounds that are chemically related. A complete list
of common and chemical names of the most recent list of herbicides published by the Weed Science
Society of America, in alphabetical order, is found in the appendices.
Table 2. CLASSIFICATION OF HERBICIDES UNDER MAJOR
CHEMICAL CLASSES
Group 1: Chlorinated Phenoxyalkanoic Acids (1-14)
1
2
3
4
5
6
7
15
16
17
18
19
20
21
22
30
31
32
33
34
35
36
37
46
47
48
2,4-D
2,4-DB
2,4,5-T
2,4,5-TB
Dichloroprop
MCPA
Erbon
Group II:
Ametryne
Atratone
Atrazine
Chlorazine
Cyanazine
Cyprozine
Desmetryne
Ipazine
Group III:
Buturon
Chlorbromuron
Chloroxuron
Cycluron
DCU
Diuron
Fenuron
Fluometuron
Group IV:
Barban
Chlorpropham
Dichlormate
8
9
10
11
12
13
14
S-Triazines (20-29)
23
24
25
26
27
28
29
Phenylureas (30-45)
38
39
40
41
42
43
44
45
Carbamates (49-50)
49
50
MCPB
Mecoprop
Silvex
Sesone
2,4-DEP
2,4-DEB
2,4,5-TES
Prometone
Prometryne
Propazine
Simazine
Simetone
Simetryne
Trietazine
Linuron
Metobromuron
Monolinuron
Monuron
Neburon
Norea
Siduron
Trimeturon
Propham
Swep
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Table 2. CLASSIFICATION OF HERBICIDES UNDER MAJOR
CHEMICAL CLASSES-Continued
Group V: Thiocarbamates (51-59)
51 Butylate 56 Pebulate
52 Cycloate 57 SMDC (metham)
53 CDEC 58 Triallate
54 Diallate 59 Vernolate
55 EPTC
Group VI: Amides (60-67)
60 Alachlor 64 Naptalam
61 Butachlor 65 Propachlor
62 Cypromid 66 Propanil
63 Dicryl 67 Solan
Group VII: Chlorinated Aliphatic Acids (68-70)
68 TCA 70 Fenac
69 Dalapon
Group VIII: Chlorinated Benzole Acids (71-76)
71 Chloramben 74 Dichlobenil
72 DCPA 75 2,3,6-TBA
73 Dicamba 76 Tricamba
Group IX: Phenols (77-81)
77 Bromoxynil 80 PCP
78 DNOC 81 loxynil
79 Dinoseb
Group X: Substituted Dinitroanilines (82-85)
82 Benefin 84 Nitralin
83 Dinitramine 85 Trifluralin
Group XI: Bipyridiniums (86-87)
86 Diquat 87 Paraquat
Group XII: Arsenicals (88-91)
88 MSMA 90 Cacodylic acid
89 DSMA 91 Sodium arsenite
Group XIII: Uracil Derivatives (92-94)
92 Bromacil 94 Terbacil
93 Isocil
16
-------
Examples of how the above classification system can be used in a decision-making process
can be illustrated. The detection of dioxin (specifically, the 2,3,7,8-tetrachlorodibenzo-p-dioxin
TCDD) in 2,4,5-T raised the question whether dioxin might be present in other herbicides. TCDD
arises in the manufacturing process during the production of the trichlorophenol (Figure 1). There-
fore it would be logical to examine herbicides in groups I and IX for dioxin contaminants. Since
TCDD formation requires high-temperature hydrolysis and a chlorine atom in the 2-position on the
ring, certain herbicides could be eliminated from groups I and IX. The chlorophenol in 2,4-D and
related dichlorophenoxy herbicides is prepared by chlorination, i.e., no elevated temperatures are in-
volved; therefore herbicides 1,2, 5,11,12, and 13 could be eliminated in group I. Those herbicides
lacking a chlorine atom in the 2-position would eliminate herbicides 6, 8, and 9 from group I and 77,
78, 79, and 81 from group IX. By the process of elimination one is left with those herbicides that
are suspect for dioxin content. Woolson et al. (1972) analyzed approximately 129 samples of 17 dif-
ferent pesticides for TCDD content and found that 76 percent of the samples analyzed contained
less than 0.1 ppm. The herbicides included in this survey were selected using the same rationale in
formulating the above-mentioned classification system. As a safety measure, 2,4-D was included in
the survey and, as predicted, was found to contain no TCDD.
ci
ONa
Figure 1. The formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)
in the production of 2,4,5-T
Another example of the use of the chemical classification system in a decision-making process
is illustrated by the azobenzenes. When propanil is added to soil in high concentrations, a number
of azobenzene-type metabolites can be isolated (Bartha and Pramer, 1967; Linke and Bartha, 1970;
and Plimmer and Kearney, 1970). Concern was expressed about the appearance of these azobenzenes
in the environment, since they are structurally related to a known carcinogen, p-dimethylamino
azobenzene. The principal azobenzene formed from propanil is 3,3',4,4'-tetrachloroazobenzene
(TCAB), which has subsequently been shown to be noncarcinogenic (Bartha and Pramer, 1970).
Nevertheless, prior to the discovery of the noncarcinogenic properties of TCAB, it was important to
know which herbicides might form azobenzenes. Propanil is first metabolized to 3,4-dichloroaniline,
which subsequently undergoes condensation with a second molecule of 3,4-dichloroaniline to form
TCAB (Figure 2). Therefore any herbicide metabolized to an aromatic amine might form azobenzenes.
TCAB
CI
Figure 2. Metabolism of propanil in soils to form 3,4-dichloroaniline (DCA) and
3,3',4,4'-tetrp~>-' - •->,- -zobenzene (TCAB)
17
-------
Here again the chemical classification system played an important role in selecting those herbi-
cides suspected of azobenzene formation. The aniline-based herbicides include the phenylureas
(group III), carbamates (group IV), and some of the amides (group VI). Various herbicides
in these groups have been examined for their potential to form azobenzenes. It was found that the
phenylureas are not metabolized to azobenzenes (Dalton et al., 1966) that certain steric factors in
the herbicide molecule prevent azobenzene formation (Bartha et al., 1968) and that azobenzene
formation is a function of concentration in soils (Kearney and Plimmer, 1972). In many cases manu-
facturers have been required to submit information on azobenzenes resulting from the metabolism
of existing or new aniline-based herbicides undergoing review for registration.
As environmental issues are raised about various herbicides, such as impurities (e.g., dioxins)
or metabolites (e.g., azobenzenes), the chemical classification system offers a valuable tool for
selecting related herbicides for examination and testing.
Chemical Properties of Herbicides
Herbicides are manufactured by synthesis from raw materials produced by the chemical indus-
try. Chlorinated aromatic compounds are of major importance for the production of a wide variety
of herbicidal compounds. Specifically, chlorinated phenols, chlorinated anilines, chlorinated benzoic
acids, and nitroanilines are of major importance as starting points for herbicide syntheses. Non-
aromatic compounds include chlorinated aliphatic acids, many heterocyclic derivatives (e.g., tria-
zines), and several organometallic compounds.
The sections that follow deal with some of the physical properties of the major herbicide
groups. Major topics discussed under each heading include synthesis, reactions, and current produc-
tion estimates, if available.
Group I: Chlorinated Phenoxyalkanoic Acids.—Herbicides in group I are derivatives of the
structure shown below:
OCHR(CH2)nCOOH
DJX
The names, formulas, and properties of the major chlorinated phenoxyalkanoic acid herbicides are
found in Table 3.
The phenoxyalkanoic acids, particularly 2,4-D and 2,4,5-T, have maintained an important
position in the herbicide market. The method of synthesis of 2,4-D is generally applicable to members
of this class. Monochloroacetic acid is reacted with 2,4-dichlorophenol (II) in the presence of aqueous
sodium hydroxide to from 2,4-D (III).
OH OCH2COOH
ci
C1CH2COOH + NaOH -» K)J + NaCl + H2O
18
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Table 3. PROPERTIES OF SOME CHLORINATED PHENOXYALKANOIC ACID HERBICIDES1
Name
2,4-D4
2,4-DB
2,4,5-T
2,4,5-TB
Dichloroprop
MCPA6
MCPB
Mecoprop
Silvex7
Sesone8
Formula2
R
H
H
H
H
CH3
H
H
CH3
CH3
OCH2
OCI
Cl
X
Cl
Cl
Cl
Cl
Cl
CH3
CH3
CH3
Cl
CH2OS03
Y
Cl
C!
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Na
Z
H
H
Cl
Cl
H
H
H
H
Cl
n
0
2
0
2
0
2
2
0
0
Melting
point (°C)
140.5
117-119
158
120-121
118
119
100
94-95
179-181
170
(free acid)
245
(Na salt)
Solubility (ppm)3
Water Acetone Ethanol Benzene
0.07 45 1.07s
46
238 590
350 59.5 85s
825 1 53s
44
600 0.472s
140 18
26.5 0.64 0.05s
2,4-DEP
" OCH2CH20-~
OCI
. Cl
P
3
200
(bpat 0.1
mm Hg)
1 Adapted from Plimmer (1970).
2 See formula I.
3 Unless otherwise stated.
4U.S. Pat. 2,390,941 (1945), to American Chemical Paint Co.
'Grams per 100 grams of solvent.
6 U.S. Pat. 2,740,810 (1956), to Diamond Alkali Co.
7U.S. Pat. 2,749,360 (1956), to the Dow Chemical Co.
8 U.S. Pat. 2,573,769 (1951), to Union Carbide and Carbon Corp.
The phenoxyalkanoic acids are crystalline solids, soluble in organic solvents. The free acids,
metal salts, amine salts, ammonium salts, or esters may be used as herbicides. Esters of 2,4-D or
2,4,5-T with n-butanol or alcohols of lower molecular weight are classed as "volatile" since their
vapor has been shown to damage plants in close proximity to treated areas. Problems associated
with volatilization can be avoided by esterifying phenoxyalkanoic acids with alcohols of higher
molecular weight or alcohols that contain polar groupings such as polypropylene glycol or
butoxyethanol.
The production of 2,4-D in 1970 was 44 million pounds, down 7.4 percent from 1969 (Fowler,
1972). The production, exports, and producers' domestic disappearance of 2,4-D and 2,4,5-T in
the United States for 1960 to 1970 are shown in Table 4.
The estimated U.S. production of 2,4-D in 1971 was 45 million pounds of the active ingredient;
2,4,5-T production was estimated at 6 million pounds (Lawless et al., 1972). The primary manu-
facturer of 2,4,5-T is the Dow Chemical Company at Midland, Michigan. Current specifications for
2,4,5-T production require a dioxin content (based on TCDD) of less than 0.1 ppm of the acid
equivalent of 2,4,5-T, but the manufacturer has refined the synthetic process to make a product
containing less than 0.1 ppm of TCDD.
19
-------
Phenoxyalkanoic acids may be analyzed by a colorimetric method that involves reaction with
chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonie acid) in concentrated sulfuric acid.
In an improved procedure the phenoxy acids are cleaved by pyridine hydrochloride, and the
liberated phenol is colorimetrically estimated after reaction with 4-aminoantipyrine in basic solution.
Conversion of free acid to the methyl ester by reaction with diazomethane or boron trifluoride in
methanol gives a derivative suitable for analysis by electron-capture gas chromatography.
Table 4. PRODUCTION, EXPORTS, AND PRODUCERS' DOMESTIC
DISAPPEARANCE OF 2,4-D AND 2,4,5-T IN THE UNITED STATES,
1960-19701
Production2
Year
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
2,4-D
36,185
43,392
42,997
46,312
53,714
63,320
68,182
77,139
79,263
47,077
43,576
2,4,5-T
6,337
6,909
8,369
9,090
1 1 ,434
11,601
15,489
14,552
17,530
4,999
(6)
Exports3-4
2,4-D and
2,4,5-T
8,796
9,085
10,192
14,657
13,037
6,924
5,419
4,410
3,391
7,287
9,571
Domestic
disappearance5
2,4-D
31,131
31,067
35,903
33,199
43,986
50,535
63,903
66,955
68,404
49,526
46,942
2,4,5-T
5,859
5,444
8,102
7,179
8,912
7,244
17,080
15,381
15,804
3,218
4,871
1 All values given in thousands of pounds.
'Source: U.S. Tariff Commission.
'Source: U.S. Bureau of the Census.
4 Excludes military shipments abroad; these are not considered exports.
5 Includes military shipments abroad.
'Separate figure not available.
The starting materials for 2,4-D production are 2,4-dichlorophenol and monochloroacetic
acid. The former is manufactured by chlorination of phenol and the latter by chlorination of a
mixture of acetic anhydride and acetic acid. Byproducts are the 2,6 isomer of dichlorophenol and
higher chlorinated phenols that can be utilized for pentachlorophenol manufacture by further
chlorination. Phenol itself can be obtained by basic hydrolysis of chlorobenzene, which is pro-
duced by direct chlorination of benzene. Thus benzene, acetic acid, acetic anhydride, chlorine,
and sodium hydroxide suffice as raw materials for 2,4-D manufacture.
The production of 2,4,5-T is similar to that of 2,4-D except that 2,4,5-trichlorophenol is re-
quired as starting material and this is manufactured by the basic hydrolysis of 1,2,4,5-tetrachloro-
benzene. Hydrolysis is carried out under pressure at an elevated temperature that must be care-
fully controlled to avoid formation of a toxic impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin.
Tetrachlorobenzene is made by direct chlorination of benzene or may be obtained as a byproduct
from the manufacture of benzene hexachloride.
20
-------
Group II : s-Triazines.— Herbicides in group II are derivatives of the structure shown below:
R3
-V
HNR2
IV
The names, formulas, and properties of the major s-triazine herbicides are given in Table 5.
Table 5. PROPERTIES OF s-TRIAZINE HERBICIDES1
Name
Ametryne3
Atratone
Atrazine4
Simazine5
Simetone3
Simetryne
Prometone3
Prometryne3
Propazine
Lambast6'7
Chlorazine7
R,
C2HS
C2H5
C2HS
C2HS
C2H5
C,H5
/-C3H7
/-C3H,
/-C3H7
NH(CH2
N(C2H5
Formula2
R,
/-C3H,
,'-C3H7
/-C3H7
C,H5
C2H5
C2H5
C2H5
/-C3H7
/-C3H,
)^OCH38->
)2 N(C2HS)2
R3
SCH3
OCH3
Cl
Cl
OCH3
SCH3
OCH3
SCH3
Cl
SCH3
Cl
Melting
point (°C)
84-86
94-96
173-175
225-227
91-92
118-120
212-214
55
Water
185
70
70
5
730
48
100
Solubility (ppm) Vapor pressure
-it °n°p
Acetone Ethanol Methanol Benzene (mm Hg)
8.14 X 10'7
18,000 3.0 X 10'7
18,000
400 6.1 X 10"'
>500,000 >250,000 2.3 X10'6
1 .0 X 1 0'6
2.9 X 10'"
Very Slightly Very
soluble soluble soluble
'Adapted from Plimmer (1970).
2See structure IV.
3U.S. Pat. 2,909,420 (1958), to J. R. Geigy Akt. Ges.
"U.S. Pat. 2,891.855 (1958), to J. R. Geigy Akt. Ges.
5Swiss Pat. 342,784 (1960), to J. R. Geigy Akt. Ges.
6 Registered trademark Monsanto Co.
7 Lambast and chlorazine have unsaturated rings.
8 For R, and R2.
The basic material for the production of s-triazine herbicides is cyanuric chloride, which is
synthesized by trimerization of cyanogen chloride. Raw materials for the synthesis of cyanuric
chloride are chlorine and hydrogen cyanide. Cyanuric chloride has three reactive chlorine atoms,
which can be successively replaced by different functional groups. More vigorous reaction condi-
tions are required for each successive replacement. The most important herbicides of this class have
two alkylamino substituents and a chloro, methylthio, or methoxy group. Atrazine is obtained by
the action of ethylamine and isopropylamine on cyanuric chloride. Reaction of atrazine with
methylmercaptan gives ametryne. These are typical triazine herbicides, but in recent years
s-triazine herbicides containing a variety of substituents have been developed.
Triazine herbicides are colorless solids, only slightly soluble in water but quite soluble in
organic solvents. Their vapor pressures are low (atrazine 3.0 X 10" 7 mm Hg at 20°C), but small
quantities may be lost by volatilization at ambient temperatures.
21
-------
Generally the triazines are unreactive, and the alkylamino groups at the 4- and 6-positions do
not react with normal acylating agents. Hydrolysis of the 2-chloro, 2-alkylthio, or 2-alkyloxy-4,6-
bis(alkylamino)-s-triazines by acid or base gives the corresponding 2-hydroxy derivative. Hydrolysis
provides a method for quantitative estimation of triazine by measurement of the absorbance at
225, 240, and 255 nanometers. The s-triazine ring is stable and is not cleaved except under drastic
conditions.
The estimated U.S. production of atrazine in 1971 was 90 million pounds of the active ingre-
dient (Lawless et al., 1972). Atrazine is thus the leading herbicide in production. The production
of simazine and propazine is estimated at 5 and 4 million pounds, respectively, during 1971. These
three s-triazine herbicides are manufactured by Ciba-Geigy Chemicals. Atrazine is manufactured at
the St. Gabriel plant in Louisiana.
Group III: Phenylureas.—Some important properties of group III herbicides are found in
Table 6.
A typical synthesis proceeds by way of an isocyanate as intermediate. The isocyanate is syn-
thesized by reaction of phosgene (V) with an aromatic amine (VI). The reaction of an isocyanate
with an amine gives a urea, whereas reaction with an alcohol gives a carbamate. The chemistry of
carbamates is discussed in a subsequent section. The synthesis of monuron is as follows:
NHCON(CH3)2
(CH3)2NH
coci2
Cl
V VI Monuron
The reaction of chloroaniline in dioxane or other inert solvent with phosgene and anhydrous
hydrogen chloride gives p-chlorophenyl isocyanate. Several methoxy ureas are used as herbicides,
and these are prepared by using O-methylhydroxylamine in place of dimethylamine. The ureas are
generally stable crystalline solids, soluble in organic solvents and slightly soluble in water. Basic
hydrolysis of a urea regenerates the parent aromatic amine. This reaction forms the basis of an
analytical method, since the free aromatic amine can be extracted into an organic solvent and
estimated. Alternatively, the liberated aliphatic amine may be distilled and quantitatively absorbed
in acid, which is then backtitrated.
The estimated production of diuron in the United States in 1971 was 6 million pounds of the
active ingredient (Lawless et al., 1972). Du Pont is the primary manufacturer of many phenylurea
herbicides. In 1971, the estimated production of fluometuron (Ciba-Geigy), linuron (du Pont), and
isorea (Hercules) was 4 million, 2 million, and 4 million pounds, respectively. The production of
chlorbromuron, chloroxuron, fenuron, monuron, and siduron was less than 1 million pounds in
each case.
Group IV: Carbamates.—The names, formulas, and physical properties of several carbamate
herbicides are given in Table 7.
22
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Table 6. PROPERTIES OF PHENYLUREA HERBICIDES1
Name
Fenuron3
Monuron4
Diuron4
Fluometuron
Linuron
Metobromuron
Monolinuron
Neburon4
X
H
Cl
Cl
H
Cl
Br
Cl
Cl
Y
H
H
Cl
CF3
Cl
H
H
Cl
Formula2
R,
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3. ^
R2
CH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
C4H9
Melting
point (°C)
133-134
174-175
158-159
180-190
(decomposition)
163-164
93-94
95.5-96
102-103
Solubility (ppm)
Water Acetone Ethanol
3850
230 52,000
42 53,000
90 3
75 500,000
330 Soluble Soluble
930
4.8
Vapor pressure
Benzene °C mm Hg
60 1.6X 1Q-"
2,900 25 5 X 10"'
1,200 30 0.31 X 10~5
100 5 X 10's
150,000
24 1.5 X 10"»
Siduron
Chloroxuron
Buturon
Chlorbromuron Br Cl
H H
H C6H4CI CH3
H Cl CH3
x>
CH,
Norea
Cycluron
CH3
,NHCON(CH3)2
OCH,
/\-NHCONH(CH3)2
133-138
151-152
145-146
94-96
170-172
138
18
3.7
30
50
150
1200
160,000
20 4 X 10"'
Soluble Soluble
'Adapted from Plimmer (1970).
2 Refers to the following structure
3U.S. Pat. 2,655,447 (1953), to E. I. du Pont de Nemours & Co., Inc.
4U.S. Pat. 2,655,445 (1953), to E. l.du Pont de Nemours & Co., Inc.
The reaction described for the synthesis of a urea may also be used for the synthesis of a car-
bamate by using an alcohol instead of an aliphatic amine in the reaction with an isocyanate. Alter-
natively, the reaction of a chloroformate ester with a primary aromatic amine gives a urea.
Although the carbamates are crystalline solids, some of them are appreciably volatile; for
example, propham volatilizes from the soil surface at field temperatures and must be incorporated
at shallow soil depths to preserve its activity.
Hydrolysis of a carbamate by acid or base gives the aromatic amine, and this reaction can be
used for analytical determination. Basic hydrolysis is preferable since acid hydrolysis is accom-
panied by decomposition and charring of the aromatic amine, and extractive separation is necessary
before the free aromatic amine can be estimated.
23
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Table 7. PROPERTIES OF SOME CARBAMATE HERBICIDES1
Name
Propham (IPC)
Melting
Formula . /0o.
point ( C)
s**~******^^ W HOnnf* W /f^Wl ft7RR
or
Solubility tppm)2
Water Acetone Ethanol
Very
soluble
Benzene
Chlorpropham (CIPC)3
38-40
Miscible Very
soluble
Cl
Barban4
Swep
Sirmate6 UC 22463
Terbutol7
C6HSNHCOOCH2C=CCH2CI 75-76 0.0011s
Cl^X^v.NHCOOCH3 133-134
Ul
^v-CH2OCONHCH3 52 170 Soluble
Cl I
Cl
C(CH3)3 200 7
^v--COONHCH3
37.0s
Soluble
'From Plimmer(1970).
2 Unless otherwise indicated.
3 U.S. Pat. 2,695,225 (1954), to Columbia Southern Chemical Corp.
4 U.S. Pat. 2,906,614 (1959), to Spencer Chemical Co.
5 Grams per 100 grams of solvent.
6 Registered trademark. Union Carbide Co.
'U.S. Pat. 3,140,167 (1964), to Hercules Powder Co.; registered trademark.
The estimated U.S. production of chlorpropham in 1971 was 2 million pounds; the production
of barban and terbutol was less than 1 million pounds each.
Group V: Thiocarbamates.—The names, formulas, and properties of some of the group V
herbicides are found in Table 8.
The synthesis of S-ethyl dipropylthiocarbamate (EPTC) is typical of synthetic methods for
the production of thiocarbamates; EPTC was first used as a herbicide in 1957.
The reaction of phosgene with di-n-propylamine (VII) gives a carbamoyl chloride (VIII), which
subsequently reacts with a thiol (as the sodium derivative) to give the corresponding thiocarbamate
(IX):
(n-C3H7)2NH + COC12 -> (n-C3H7)2NCOCl + HC1
VII VIII
24
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Table 8. PROPERTIES OF SOME THIOCARBAMATE HERBICIDES1
Name
EPTC"
SMDC5
Vernolate4
CDEC7
Pebulate8
Dial late
Trial late
Butylate
Molinate
Cycloate9
Formula
(C3H7)2NCOSC2H5
CH3NHCSSNa2H2O
(C3H7)2NCOSC3H,
* NCOSC3H7
/CH3\ \
CHI NCOSCH,CCI=CHCI
\CH,/ I
I 3XCH|NCOSCH2CCI=CCI,,
\CH3/ /,
/CH3\ \
( CH2CHJ NCOSC2H5
/| NCOSC2H5
j^^N— NCOSC2HS
Solubility (ppm)3 Vapor pressure2
Boiling
P°mt Water Acetone Ethanol Benzene °C mm Hg
12720 375 Miscible Very 24 1.97XKT2
soluble
72.2s
14020 109 24 5AX. 10'3
128-130, 92 Soluble Soluble 200 2.2 X10"3
14220 30 Miscible Miscible 25 4.8 X 10'3
1509 14 Miscible
148, 4 Soluble Soluble
137.5,,
137,0 1000 Miscible
146,0
'Adapted from Plimmer (1970).
aThe subscripts give the pressure in millimeters of mercury.
'Unless otherwise indicated.
"U.S. Pat, 2,913,327 (1959), to Stauffer Chemical Co.
SU.S. Pat. 2,791,605 (1957), to Stauffer Chemical Co.
"Grams per 100 milliliters.
'U.S. Pat. 2,919,182 (1959), to Stauffer Chemical Co.
8 U.S. Pat. 3,175,897 (1965), to Stauffer Chemical Co.
'U.S. Pat. 3,185,720 (1965), to Stauffer Chemical Co.
NaCl
IX
Thiocarbamates are generally somewhat volatile; the vapor pressure of EPTC is 2 X 10~2 mm
Hg at 24°C compared with 6 X 10~9 mm Hg for simazine. Losses from soil were found to be propor-
tional to the vapor pressure of the thiocarbamate but may be influenced by formulation. Greater
losses from wet soil as compared to dry have been ascribed to the binding or adsorption of the pesti-
cide on dry soil. Soil moisture occupies adsorption sites in wetter soils, and the unadsorbed herbicide
is lost by volatilization into the atmosphere.
Generally, acid hydrolysis of the thiocarbamates liberates free amine, which can be distilled
from the reaction mixture after it has been made alkaline. Quantitative estimation of the thiocarba-
mate is based on the amount of amine produced, which is readily determined colorimetrically by
reaction with cupric dithiocarbamate.
25
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Group VI: Amides.—The names, formulas, and properties of several important amide herbi-
cides are found in Table 9.
Aromatic amides may be synthesized by the reaction of an acid chloride with an amine. This
synthetic pathway is utilized for the production of a number of substituted anilide herbicides, such
as 3',4'-dichloropropionanilide (propanil, X) used for weed control in rice.
C2H5COC1 +
Cl
X
The anilide herbicides may be hydrolyzed to the free aromatic amine which can be estimated
colorimetrically after diazotization and coupling.
Several herbicides are synthesized from secondary amines, and these are generally chloro-
acetamide derivatives of the type C1CH2CONR1R2, where Rj is an alkyl group and R2 an aromatic
or an alkyl group. In the simplest case R^ = R2 = C2H5 (CDA). It has been suggested that such
herbicides owe their effectiveness to their ability to react with enzymatic sulfhydryl groups in plants.
The estimated production and manufacturers of several important amide herbicides in the
United States in 1971 are as follows: propachlor, 23 million pounds (Monsanto); alachlor, 20
million pounds (Monsanto); CDAA, 10 million pounds (Monsanto); propanil, 6 million pounds
(Monsanto; Rohm & Haas); and diphenamid, 3 million pounds (Blanco and Upjohn) (Lawless
etal., 1972).
Groups VII and VIM: Chlorinated Aliphatic and Benzoic Acids.—Due to certain chemical
similarities, the chlorinated acid herbicides are discussed together in this section. The names, for-
mulas, and properties of the chlorinated aliphatic acid herbicides are found in Table 10.
Herbicides of simple chemical structure are represented by chlorinated derivatives of aliphatic
acids, such as trichloroacetic acid (TCA) and 2,2-dichloropropionic acid (dalapon). The acids are
hydrolyzed in solution at room temperature, and, at physiological pH, a chlorine atom can be re-
placed by a hydroxyl group. Trichloroacetic acid breaks down in solution to form chloroform
and carbon dioxide. Dry dalapon sodium salt is stable, but aqueous solutions are subject to decom-
position, giving rise to pyruvic acid and a chloride ion. The Dow Chemical Company is the pro-
ducer of dalapon and TCA, and an estimated 5 million pounds of dalapon as compared with less
than 1 million pounds of TCA for herbicide use were produced in the United States in 1971
(Lawless et a/., 1972).
The names, formulas, and properties of the chlorinated benzoic acids are found in Table 11.
Chlorinated benzoic acids and their derivatives form a heterogeneous group of compounds,
including 2,3,6-trichlorobenzoic acid, 3,6-dichloro-2-methoxybenzoic acid (dicamba), and a
number of benzonitrile (cyanobenzene) derivatives. The derivatization of the acids by reaction
with diazomethane or boron trifluoride/methanol gives methyl esters that are useful for gas-
chromatographic analysis. The acids are generally high-melting-point solids and are moderately
soluble in water, especially as salts.
Amiben (3-amino-2,5-dichlorobenzoic acid) is an aromatic amino acid of economic importance
first registered in the United States in 1960. For its manufacture 2,5-dichlorobenzoic acid is
26
-------
Diphenamid5
Table 9. PROPERTIES OF AMIDE HERBICIDES1
Name
Solan3
Dicryl
Propanil
.... Solubility (g/1 00 g solvent)2 Vapor pressure
Melting
Formula . ,o_,
Water Acetone Ethanol Benzene °C mm Hg
NHCOCHC3H7 85-86 8-94
C|J0 °H'
CH3
NHCOC=CH, 127-128 Insoluble 20
if^l ^3
Cl
NHCOC,H5 93-94 500
«¥
134-135 0.5"
15"
CHCON(CH3)2
Propachlor
Alachlor
CDAA7
.
COCHjCI
X
67-76
CH,OCH,
VCOCH,CI
M
] ns
CH,CICON(CH,CH-CH,), 74(
7004
30.9
50
110 0.3
50-
20 QAX 10-l
COOH 185 200
NHCO-<] 131 <0.01
5000
1 Adapted from Plimmer (1970).
2 Unless otherwise stated.
3U.S. Pat. 3,020,142 (1962), to F.M.C. Corp.
4Parts per million.
5U.S. Pat. 3,120,434 (1964), to Eli Lilly and Co.
6 Boiling point at 0.03 mm Hg.
7U.S. Pat. 2,864,683 (1958), to Monsanto Chemical Co.
8 Boiling point at 0.3 mm Hg.
'U.S. Pats. 2,556,664 and 2,556,664 (1951), to U.S. Rubber Co.
27
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Table 10. PROPERTIES OF CHLORINATED ALIPHATIC ACID HERBICIDES1
Name
TCA
Dalapon3
Fenac4'5
Formula
CCI3COOH
CCI3COONa
CH3CCI2COOH
CH3CCI2COONa
CH2COOH
,. . „ ... Solubility (g/100g solvent)
Mpltmg Rnilmg
point (°C) point (°C) ... .
^ Water Acetone
59 197.52 1306 850
833 0.76
185-190 Very soluble
193-194 502 0.014
159-160 Slightly soluble
Benzene
201
0.007
0.002
1 Adapted from Plimmer (1970).
2 Vapor pressure at 76.99°C, 5.0 mm Hg.
3U.S. Pat. 2,642,354 (1953), to the Dow Chemical Co.
4 A mixture of isomers; data refer to the 2,3,6-trichloro isomer.
5U.S. Pat. 2,977,212 (1961), to Heyden Newport Chemical Corp.
nitrated to yield 2,5-dichloro-3-nitrobenzoic acid. The nitro compound is then reduced to the 3-
amino compound: isomeric nitro compounds must be removed by careful purification since they
reduce the selectivity of amiben. Amiben may function as an acid or an aromatic amine. In
aqueous solution amiben rapidly darkens on exposure to light, but it is quite stable in the solid
state.
2,6-Dichlorobenzonitrile (dichlobenil) is made by the chlorination of 2,6-dichlorotoluene.
Hydrolysis of the product to 2,6-dichlorobenzaldehyde is followed by conversion to the oxime,
which on dehydration with acetic anhydride gives the nitrile. Dichlobenil is a crystalline, relatively
volatile solid. Hydrolysis with base converts it to 2,6-dichlorobenzoic acid.
The estimated U.S. production of several chlorinated benzoic acids in 1971 was as follows:
amiben, 20 million pounds (Amchem), dicamba, 6 million pounds (Velsicol), and DCPA, 2 million
pounds (Diamond) (Lawless et al., 1972).
Group IX: Phenols.—The names, formulas, and properties of several phenolic herbicides
are found in Table 12.
4-Cyano-2,6-dibromophenol (bromoxynil, XIa) and 4-cyano-2,6-diiodophenol (ioxynil, Xlb)
can be synthesized by the following reactions:
OH
XI
a: X = Br
b: X = I
28
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Table 11. PROPERTIES OF CHLORINATED BENZOIC ACIDS1
Name
Amiben3
Formula
NH2
/^. Cl
JQT
Cr^^COOH
Melting
point ( C)
210
Solubility (g/100g
Water Acetone
7004 23.27
solvent)2
Ethanol Benzene
17.28 2004
Vapor pressure
°C mm Hg
DCPA5
Dicamba6
Tricamba
OOCH3 156 <0.54
^ (decomposes
OT at 360-370)
COOCH3
COOH 114-116 0.45
COOH
139-139
10
25 40 0.01
92.2
100 3.75 X 10
1-3
Slightly soluble
Dichlobenil7
2,3,6-TBA8 COOH
Cl 1 Cl
O
139-145
125-126
184
0.84
20 5.5 X 10~4
60.7
23.8
1 Adapted from Plimmer (1970).
2 Unless otherwise stated.
3U.S. Pat. 3,014,063 (1958), to Amchem. Products Inc.
4Parts per million.
5 U.S. Pat. 2,923,634 (1960), to Diamond Alkali Co.
'U.S. Pat. 3,013,054 (1961), to Velsicol Chemical Corp.
'U.S. Pat. 3,027,248 (1962), to North American Philips Co., Inc.
8 U.S. Pat. 2,848,470 (1956), to Heyden Newport Chemical Corp.
PCP is manufactured by catalytic chlorination of phenol. Dinitrophenols are prepared by the con-
trolled nitration of an alkylated phenol. Nitrophenols may present the hazard of explosion if
completely dry. They form water-soluble salts of alkali metals and may be readily reduced to the
monoamino nitro derivatives. They form typical molecular compounds with amines, hydrocarbons,
and phenols. They are susceptible to decomposition by ultraviolet irradiation in alkaline solution.
PCP decomposes in sunlight.
PCP may contain relatively large concentrations (<1000 ppm) of the higher chlorinated dioxins,
that is, the hexa-, hepta, and octachlorodibenzo-p-dioxins (Woolson et al, 1972). However, 2,3,7,8-
tetrachlorodibenzo-p-dioxin was not detected in PCP. Studies are underway to reduce the dioxin
29
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Table 12. PROPERTIES OF PHENOL HERBICIDES1
Name
Bromoxynil
loxynil
PCP4
DNOC
Dinoseb
,, . . Solubility (g/1 00 g solvent)2 Vapor pressure
Formula . .0"
Water Acetone Methanol Ethanol ' °C mm Hg
CN 194-195 53 17 9
OH
CN 212-213.5 503 7 2
A
OH
OH
CI^TCI 190-191 20-253 100 0.12
CIJCI
Cl
OH 85.8 1303 25 105X10"6
N02
OH CHs 38-42 0.0052 48 151 1.0
02N Js.,CHC2Hs
N02
'Adapted from Plimmer (1970).
2 Unless otherwise stated.
'Parts per million.
4U.S. Pat. 2,131,259 (1938), to the Dow Chemical Co.
content of PCP, with a total content in the 100-ppm range. The hexa-, hepta-, and octachloro-
dibenzo-p-dioxins are considerably less toxic than the 2,3,7,8-tetrachloro isomer. The hexa isomer
has been implicated as the factor responsible for chickedema.
Estimated U.S. production of PCP in 1972 as a herbicide, desiccant, molluscicide, and termite
controller was 46 million pounds. The herbicidal production of dinoseb was 3 million pounds.
Group X: Dinitroanilines.—The names, formulas, and properties of several dinitroaniline
herbicides are found in Table 13.
Dinitroaniline derivatives have been used since 1963, when the herbicidal use of a,a,a-trifluoro-
2,6-dinitro-JV,JV-di-n-propyl:p-toluidine (trifluralin) was reported. This compound is typical of a
number of related AT-alkyl-2,6-dinitroaniline derivatives that have been developed in recent years.
Synthesis depends on the formation of substituted 2,6-dinitrochlorobenzene (XII), which under-
goes reaction with an amine to yield a substituted 2,6-dinitroaniline (XIII).
30
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Table 13. PROPERTIES OF SUBSTITUTED DINITROANILINE HERBICIDES1
Name
Formula
Boiling
Melting
point (°C) point ("C)
°2
Solubility in _
water (ppm)3 0
Vapor pressure
r r
mm Hg
Benefin C2HS-N-CH2CH2CH2CH3 65-66.5 121-122OS
02N^vN02 148'1497
TOT
7025 25 4X 1(T7
Trifluralin
N(CH2CH2CH3)2 48.5-49
96-970.i8
127 24.5 1.99XKT4
Nitralin
CF3
N(CH2CH2CH3)2
151-152
0.6
25
25
1.5X 10~6
1 Adapted from Plimmer (1970).
"The subscripts give the pressure in millimeters of mercury.
3 All three compounds listed are soluble in acetone and slightly soluble in ethanol.
NRR'
OT + NHRR'
NO,
+ HC1
XII
XIII
R and R' = alkyl
Dinitroaniline herbicides are bright-yellow or orange crystalline solids and are generally of low
solubility in water. Trifluralin is slightly volatile and is also subject to photodecomposition. There-
fore it is normally applied as a herbicide by incorporation in the soil. The alkyl groups can be re-
moved by irradiation or by the action of enzymes.
Trifluralin production has increased steadily over the last 9 years, with an estimated U.S. pro-
duction of 25 million pounds in 1971 (Lawless et al., 1972). Nitralin production is estimated at
8 million pounds and that of benefin at less than 1 million pounds.
Group XI: Bipyridiniums.—The structures of diquat (l,l-ethylene-2,2'-bipyridinium, XIV)
and paraquat (l,l'-dimethyl-4,4'-bipyridinium, XV) are shown below:
31
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XV
Paraquat melts at 175° to 180°C and is soluble in water but insoluble in organic solvents. Diquat
melts at 335° to 340°C and decomposes at higher temperatures. It is very soluble in water and
slightly soluble in acetone.
Bipyridinium herbicides are synthesized by the reduction of pyridine with sodium in liquid
ammonia, which gives an ion radical that is oxidized to 4,4'-bipyridine (XVI), and quaternization
with methyl bromide yields paraquat. Raney nickel reduction of pyridine gives 2,2'-bipyridine
(XVII), which is quaternized with ethylene dibromide to give diquat.
o
N
Na/NH3 / \ Raney Ni/H2
XVI XVII
CH3Br I C2H4
Imports of diquat and paraquat from Imperial Chemical Industries Ltd. (England) in 1969
were almost 750,000 and almost 3 million pounds, respectively (Lawless et al., 1972).
Group XII: Arsenicals.-The structures of MSMA/DSMA (XVIII) and cacodylic acid (XIX)
are shown below:
O CH3
H ^ONa i d
CHn-AsC CH3-As-OH
6 OH(Na) d ii
XVIII XIX
DSMA is the sodium salt of MSMA (methanearsonic acid). Cacodylic acid (hydroxydimethylarsine
oxide) is also marketed as the sodium salt. MSMA is a white crystalline solid that melts at 132° to
139°C and is extremely soluble in water (25.6 percent by weight). Cacodylic acid is a colorless
crystalline solid that melts at 200°C and is extremely soluble in water (66.7 percent by weight).
Methanearsonic acid is prepared commercially by reacting sodium arsenite with methyl
chloride under pressure at 60° C. Cacodylic acid is prepared by reacting dimethylarsine trichloride
[(CH3)2AsCl3] with water.
32
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Estimated U.S. production of MSMA/DSMA in 1971 was 35 million pounds (Lawless et al,
1972). Production of cacodylic acid was approximately 2 million pounds.
Group XIII: Uracil Derivatives.—The structures of 5-bromo-3-sec-butyl-6-methyluracil
(bromacil, XX), 5-bromo-3-isopropyl-6-methyluracil (isocil, XXI), and 3-tert-butyl-5-chloro-6-
methyluracil (terbacil, XXII) are shown below:
H H H
I I I
o ur'MO Hr'tcn
O H3C N^O H3C^W^°
O CH3 O O
XX XXI XXII
Uracil derivatives are prepared by the condensation of acetoacetic acid with a substituted urea.
The resulting methyl uracil is then halogenated. Some physical properties of the substituted uracils
are found in Table 14.
Table 14. PROPERTIES OF URACIL HERBICIDES
Name
Isocil
Bromacil
Terbacil
Molecular
weight
247.1
261.1
216.7
Melting
point (°C)
158-159
1 58-1 59
175-177
Solubility in
water at 25°C (ppm)
2150
815
710
Residues of the uracil derivatives in soils, water, and animals are measured by gas chromatog-
raphy, using microcoulometric and electron-capture detectors with a sensitivity of 0.1 to 0.01 ppm.
Estimated U.S. production of bromacil and terbacil in 1971 was 8 million and 1 million
pounds, respectively.
Contaminants
The contamination of herbicides can arise through a number of causes. The product of a syn-
thetic chemical reaction in the laboratory or in an industrial plant is seldom a pure compound. The
product, which may be referred to as a "technical" product, can contain appreciable amounts of
other compounds also produced by the reaction of the raw materials in numerous side reactions.
The contaminant may have undesirable properties. For example, 2,3,7,8-tetrachlorodibenzo-p-
dioxin (TCDD) may be found as a contaminant in 2,4,5-trichlorophenol, one of the starting mate-
rials for 2,4,5-T, if the reaction temperature is allowed to rise above an optimum value during the
hydrolysis of 1,2,4,5-tetrachlorobenzene. TCDD is extremely toxic to mammals and birds, and its
presence in quantities of a few parts per million is undesirable since its rate of degradation is slow.
Samples of 2,4,5-T containing 27 ± 8 ppm TCDD were found to be teratogenic in rats and mice.
The herbicide 2,4-D may be contaminated with the isomeric 2,6-D (2,6-dichlorophenoxy-acetic
acid) unless careful control of the process is maintained. 2,6-D is more resistant to biological
33
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degradation than is 2,4-D. Technical grade 2,4,5-T typically contains 90 to 92 percent 2,4,5-
trichlorophenoxyacetic acid and 8 to 10 percent impurities. The detailed composition of technical
material given by one producer was included in the Office of Science and Technology report on
2,4,5-T (1971). The impurities found in 2,4,5-T are shown in Table 15.
Table 15. IMPURITIES FOUND IN 2,4,5-T
Compound Percent by weight
2,4,5-Trichlorophenoxyacetic acid 91.0± 1.0
2,4,5-Trichloroanisole 0.5 ±0.1
5-Methoxy-2,4-dichlorophenoxyacetic acid 2.0 ± 0.5
2-Methoxy-4,5-dichlorophenoxyacetic acid 2.0 ± 0.5
2,4,5-Trichlorophenol 0.3 ± 0.1
Bis(2,4,5-trichlorophenoxyacetic acid) 3.0 ± 0.5
2,5-Dichlorophenoxyacetic acid 0.3 ± 0.1
Sulfate(SO4) 0.2 ±0.1
Sodium salt of 2,4,5-T 0.2 ±0.1
Water 0.5 ± 0.2
Tetrachlorodibenz-p-dioxin (TDD) <1 ppm
Other herbicides have been shown to contain contaminants that arise during manufacture; if
these are phytotoxic or behave very differently from the parent in their toxicology, movement in
soil, rate of microbial breakdown, or potential for bioaccumulation, further purification is usually
necessary. Removal of such contaminants does not prevent the possibility of further contamination
with other pesticides at the factory, at the formulating plant, or in storage. If two compounds are
processed in the same plant, vapor contamination may occur. Some phenoxyalkanoic acid esters
are sufficiently volatile to present serious problems if they are stored in the same area as other
agricultural chemicals. The use of dirty equipment, improperly cleaned recycled drums, and im-
properly cleaned spray equipment are all further sources of cross-contamination. The cause of con-
tamination must therefore be sought at every stage of pesticide manufacture, handling, and use.
Herbicide Metabolism
Metabolism involves the biological transformation of chemical entities through a variety of
intermediate substances until one or more final end products are obtained. In the case of herbicides
these end products may be carbon dioxide, water, and a chloride ion or a terminal residue of more
complex and stable configuration. Nearly all herbicides are at least partially metabolized by some
plant, animal, or soil-microbial system. Indeed, metabolism represents a major route of degradation
for many herbicides. The factors that render a herbicide biodegradable are not well understood.
Slightly water-soluble, highly chlorinated pesticides are generally most resistant to microbial attack.
Many of the chlorinated hydrocarbon insecticides fall into this category. The introduction of such
polar groups as —OH, — NH2, —CON<, —COO—, and — NO2, common to many herbicides, often
affords biological systems a site of attack. Catalysts facilitating these reactions are all induced and
constitutive cellular enzymes. As some organisms metabolize certain compounds only in the presence
of other energy sources, the process of cometabolism is recognized as an important mechanism of
metabolism for certain herbicides.
The principal reactions associated with the metabolism of herbicides include dealkylation,
dehalogenation, amide or ester hydrolysis, oxidation, reduction, aromatic ring hydroxylation, ring
cleavage, and condensate or conjugate formation. Many of these reactions, the enzymes, the
34
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pathways, and the intermediate products involved in herbicide metabolism have been investigated
and described in some detail (Kearney and Kaufman, 1969).
Detoxication and excretion may be the ultimate results of some metabolic processes. The
formation of glycosides and glucuronides by many organisms constitutes a mechanism for detoxica-
tion. The glycosides and glucuronides of herbicides are generally more water soluble than the parent
herbicide molecule and are therefore more readily excretable by living organisms. Ultimate degrada-
tion of these conjugates may be accomplished by other organisms. At present, however, little is
known about the subsequent fate of such compounds once they are liberated into the environment.
Condensates are sometimes formed during the metabolism of some herbicides in soil, notably the
aniline-based herbicides. The formation of these products, however, appears to be a function of
the initial application rate. Excessively high application rates of these materials result in the forma-
tion of large amounts of the condensate-type compounds, whereas very little, if any, are formed at
low or normal application rates.
Many organisms obtain energy for other life processes in the metabolism of chemicals. The
initial metabolic reactions of many herbicides often require an expenditure of energy by the orga-
nism. Only when the herbicide is fragmented into compounds that can be channeled into oxidative
cycles (e.g., the Krebs cycle) does the organism derive any useful energy. The complete oxidation
of a chemical to carbon dioxide and water, although perhaps desirable from a "complete degrada-
tion" point of view, may be a wasteful process. Actually by a series of intermediate processes the
energy originally incorporated into chemical bonds in herbicides may be transferred into ecologi-
cally acceptable products that can be used beneficially by many organisms when needed. Thus the
overall trend in herbicide metabolism is toward less complex molecules. It follows that fragmenta-
tion of the pesticide molecule through metabolism generally results in detoxication and the forma-
tion of utilizable products. This is exemplified by the ultimate degradation of (1) 2,4-D to alanine
and succinic acid, (2) dalapon to pyruvate and alanine, (3) dodine to creatine, and (4) TCA to
serine. This represents the ultimate conversion of the pesticide to an ecologically acceptable
metabolite.
Only in a few instances are the toxicological properties of one or more of a given herbicide's
metabolites actually known. Although the general trend of herbicide metabolism is toward increas-
ingly less toxic molecules, in some instances the toxicity of the metabolite may be equal to or
greater than that of the parent pesticide molecule. Some pesticides, such as the herbicide sesone
and probably 2,4-DEP, MCPES, 2,4-DEB, and 2,4-TES, are not biologically active themselves but
actually require metabolic hydrolysis for activation to a phytotoxicant. In nearly all cases, however,
even the more toxic metabolite is ultimately degradable to an ecologically acceptable entity.
The major emphasis in metabolic work has been to elucidate the pathway by which organisms
convert metabolites to successively simpler and usually more polar products. The significance of
these metabolites is a subject of considerable debate. If a metabolite is toxic or extremely persist-
ent, or represents a major residue (e.g., more than 10 percent of the parent material), its distribu-
tion and impact on the environment should be ascertained.
REFERENCES
Bartha, R., and Pramer, D., Science, 156, 1617 (1967).
Bartha, R., and Pramer, D., Adv. Appl. Microbiol., 13, 317-341 (1970).
Bartha, R., Linke, H. A., and Pramer, D., Science, 161, 582 (1968).
Bonnet, M.,Bull. Depart, de I'Aisne Sta. Agron., Laon., 1897, 68-69.
Dalton, R. L., Evans, A. W., and Rhodes, R. C., Weeds, 14, 31 (1966).
Fowler, D. L., The Pesticide Review 1971, Agricultural Stabilization and Conservation Service, U.S.
Department of Agriculture, Washington, D.C., 1972.
35
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Herbicide Handbook of the Weed Science Society of America, 2nd ed., W. F. Humphrey Press, Inc.,
Geneva, N.Y., 1970.
Kearney, P. C., and Kaufman, D. D., Degradation of Herbicides, Marcel Dekker, Inc., New York,
1969.
Kearney, P. C., and Plimmer, J. R., J. Agr. Food Chem., 20, 584 (1972).
Kogl, F., Haagen-Smit, A. J., and Erxleben, H., Z. Physiol. Chem., 90, 228 (1934).
Lawless, E. W., von Rumker, R., and Ferguson, T. L., The Pollution Potential in Pesticide Manu-
facturing, Environmental Protection Agency Technical Studies Report TS-00-72-04,1972.
Linke, H. A. B., and Bartha, R.,Bacteriol. Proc., 70, 9 (1970).
Plimmer, J. R., in Encyclopedia of Chemical Technology, Vol. 22, Wiley and Sons, Inc., New York,
1970.
Plimmer, J. R., and Kearney, P. C., J. Agr. Food Chem., 18, 859 (1970).
Timmons, F. L., Weed Science, 18, 294 (1970).
Woolson, E. A., Thomas, R. F., and Ensor, P. D., J. Agr. Food Chem., 20, 351-354 (1972).
Zimmerman and Hitchcock, Contrib. Boyce Thompson Inst., 12, 321-343 (1972).
ANALYSIS OF HERBICIDES
Introduction
Herbicides are used to remove or prevent the growth of unwanted vegetation from areas where
weeds compete with crops for nutrients, water, or light—or from areas where no vegetation is de-
sired. Once the herbicide is applied, we are confronted with a residue situation. A small portion of
the herbicide enters the air either during application or by the vaporization of surface residues.
Some of the applied material falls onto the surrounding vegetation, but most of it falls onto or even-
tually reaches the soil. If the herbicide is applied near or over water, residues are probably present
in the water. The concentrations of the residues decrease with time because of microbial activity,
chemical degradation, dilution, and plant or animal metabolism.
It is important that we know the fate of these residues. Their persistence in soil determines
whether further control is necessary and can also determine the choice of the next crop to be
planted on the treated field. Residues in the air may be carried to other fields or may be inhaled by
animals and humans. Residues in or on vegetation may be ingested by grazing animals or by con-
sumers after harvest. Residues in the water may concentrate in marine animals, or, if the water is
used for irrigation, the herbicide may adversely affect the irrigated crop.
Measurement of the residues in these substrates requires suitable methods of analysis. The
methods must be accurate, to provide the most reliable data; they should be sensitive enough for
measurement down to levels at which residues become insignificant; and they should be specific.
In applying these criteria to residue analysis, problems have been encountered. The analytical
chemist assigned to devise a general method of analysis for herbicide residues is faced with a vir-
tually impossible task. Over 100 compounds are used as herbicides, each with its own chemical
characteristics. They range from completely ionic to nonionic types. This diversity of chemical
properties makes it difficult to devise a general method of analysis applicable to all herbicides.
Over the years, methods of analysis have been developed for individual herbicides. This devel-
opment was more or less dictated by federal regulations for the establishment of pesticide toler-
ances. The only requirements were a method that would determine residues of the herbicide in the
treated crops and that could be used for the enforcement of any set tolerance. Specificity could be
claimed by citing the agricultural registrations that eliminate the presence of similar herbicides on
the crops of interest. Specificity might also be conferred by various forms of separation techniques
in the method that limit the number of interfering compounds to a small number.
36
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In a monitoring program it would exceed the manpower and funding resources of any labora-
tory to use these individual herbicide methods on every sample. Multiresidue methods are a "must"
for monitoring, and the wider the applicability of the methods, the better. Development of multi-
residue methods has been pursued mainly by governmental agencies. Progress has been slow because
of the complexity of the problem, the lower priority of the problem in comparison with the more
toxic insecticides, and the lack of manpower.
If a general herbicide procedure cannot be devised, the next approach is to develop general
analytical methods for groups of related herbicides. Several such methods have already been re-
ported. The method for chlorophenoxy acids and various acidic phenols has been used by the Food
and Drug Administration in their total diet program (Yip, 1971). A similar method for these com-
pounds is available for water analysis (Devine and Zweig, 1969). Methods for the determination of
substituted ureas (Dalton and Pease, 1962; Katz, 1966; Baunok and Geissbuehler, 1968; McKone,
1969) and herbicidal carbamates (Onley and Yip, 1971) have been developed but have not been
generally used because they are either too complex, too new, or unsuitable for the purpose. Proce-
dures for s-triazines and dinitroanilines are in the testing stage.
The development of methods for the analysis of herbicide residues is further complicated by
the tendency of herbicides and their metabolites to combine with plant or animal consitutents or
soil particulates. It is entirely possible for the bulk of the residue in a sample to be in this combined
form; if the method does not take this into account, the residue would pass undetected. Where this
type of complexing is known to occur, hydrolysis steps have been introduced into the procedure to
liberate the bound herbicide for determination as part of the residue.
The situation is further complicated by formation of new products resulting from the action of
microorganisms or sunlight on the residue. Such products may be of greater toxicological signifi-
cance than the parent compound, yet can go undetected because the method had not been designed
to include them. If these products are in the soil, they can be absorbed by the plant root system
and translocated throughout the plant, where again they can go undetected.
Current Methodology
Current residue methods usually consist of three parts: extraction, cleanup, and determina-
tion. Residues in soil, however, can also be demonstrated by growing plants susceptible to herbi-
cides on the soil; by observing the degree of growth inhibition or growth distortion, the concentra-
tion of the residue can be estimated. Such bioassay methods can be sensitive to less than 0.1 ppm
of residue in the soil, but they are not specific and it takes time to obtain an answer.
Chemical methods usually begin with an extraction step using either a polar or a nonpolar
solvent. With soil samples and certain types of low-moisture foods, Soxhlet extraction is an effi-
cient process for removing the residue. Water samples are usually extracted with a nonpolar solvent
to separate the residue from the bulk of the sample. To determine very low residue levels (parts per
billion), liter quantities may be required. Charcoal has been used to adsorb residues from water,
after which the pesticides are recovered by extracting the charcoal. The efficiency of this adsorp-
tion and desorption process has not been established. The use of polyurethane-foam plugs has
been suggested for the same purpose; although preliminary evidence seems to indicate that these
plugs may be adequate, more supporting data are needed (Gesser et al., 1972; Uthe et al., 1972).
Soils, plants, and foods have been extracted by blending the sample with the extracting sol-
vent. Nonpolar solvents will extract much of the waxes, fats, and oils along with the residue, thus
necessitating rigorous cleanup steps. The efficiency of nonpolar solvent extractions is enhanced
considerably if alcohol is also added to the sample. Polar solvents will also extract some plant
materials, but their effectiveness has already been well documented.
37
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These extraction procedures have been developed principally for the intact herbicides and
some of their metabolites. The presence of residues bound to soil particles or to tissue constituents
requires special treatment to liberate the residue before extraction. Such procedures have been
devised for several herbicides but have not been adapted for any multiresidue method.
Herbicide residues in air are removed by forcing volumes of air through a scrubbing device.
Through the use of impactors and impingers, the residues are trapped in a solvent from which they
are eventually removed. The effectiveness of these devices is difficult to measure, and, until recov-
ery data can be obtained, present data on residues in air may not be completely reliable. Inter-
ferences from other chemicals in the air may cause additional problems.
After an extract is obtained, the residue must usually be further purified, especially when the
extract is highly colored or contains large amounts of fats and waxes. Extracts of water and air may
not require further cleanup before the determinative step. For most samples, however, some type
of cleanup is necessary.
Adsorption chromatography has consistently been applied for cleanup. In this technique the
sample extract is adsorbed onto an activated adsorbent substance; then the residue is removed from
the adsorbent by a system that favors its removal over that of the extraneous materials. Chromatog-
raphy is usually accomplished on a column that has been packed with the adsorbent and the sample
placed on top. Cleanup can also be done by thin-layer chromatography (TLC) using glass plates
coated with the adsorbent and spotting the sample near the bottom edge, then developing the plate
in an ascending direction with solvent. Areas of adsorbent on the plate are scraped off and washed
to remove the residue for more definitive tests.
Such separation schemes are normally devised by using standards. Analysts should be aware of
the pitfalls in using these schemes. The presence of extraneous materials in the extracts can modify
the adsorbent or the partition coefficient sufficiently to change the elution rate or pattern by taking
up many of the active sites on the adsorbent. It may be necessary to amend the analytical scheme
to offset these effects. On samples containing large amounts of waxes and fats, it may be necessary
to repeat the chromatographic cleanup step or to take a smaller sample for the initial cleanup and
concentrate the residue to a volume suitable for the determinative step.
Current Instrumentation
Gas-liquid chromatography (GLC) continues to be the technique of choice for the rapid and
efficient separation of herbicide residues from the sample. Coupled with a selective detection sys-
tem, this technique is almost ideal for determining the concentration of the residue. Herbicides that
can be analyzed by gas chromatography will pass through the chromatographic column at a speed
governed by their distribution coefficients between the liquid and gas phases, by the temperature of
the column, and by the rate of gas flow through the system. Each herbicide will elute from the
column with a unique speed based on set operating conditions, which is why gas-liquid chromatog-
raphy is such an excellent technique for multiresidue determinations.
Detectors impart to the gas chromatograph the requisite sensitivity and selectivity for residue
work. Numerous types have been developed: electron capture, flame thermionic, flame photo-
metric, microcoulometric, electrolytic conductivity, and mass spectrometric. Each detector has a
useful function in herbicide analysis. Some can detect extremely small amounts (picogram) of resi-
due but lack specificity. Others are specific but lack sensitivity. Flame-photometric detection is
both specific and sensitive for phosphorus compounds. Electrolytic conductivity detection can be
made both sensitive and specific for nitrogen. Regardless of which detector is used, the analyst
should know^the limitations of the detector used.
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Despite improvements in instrumentation, gas-liquid chromatography is still somewhat of an
art. The properties of a column are not constant; performance will gradually change as samples are
continually introduced. The interpretation of the results requires a certain degree of judgment on
the part of the analyst. Experience will enable the analyst to assess the significance of a peak in
comparison to the noise level, the presence of other peaks, and the chemistry of the analytical pro-
cedure—and to suggest alternative procedures to answer the questions of quantity and identity.
That a gas-liquid-chromatography peak of an unknown residue has the same retention time as that
of a known standard does not necessarily mean that the two are the same. Retention time alone is
not unequivocal proof of identity.
The electron-capture or affinity detector is the most widely used, not only because it is
capable of detecting picloram amounts but also because it is stable and easy to use. It is not a com-
pletely specific detector, and the response is dependent on the number of electronegative groups on
the molecule and the molecular configuration.
The flame-ionization detector is widely used in areas other than pesticide analysis. It is a
general, nonspecific type of detector responding to carbon. This response makes it useful for
detecting herbicide metabolites of unknown structure. If, however, an alkali salt is placed in the
vicinity of the flame, response is enhanced for compounds containing phosphorus and nitrogen (Ives
and Giuffrida, 1967; Tindle et al., 1968). This detector has been used for s-triazines and carba-
mates. If a photometric cell is placed at right angles to the flame, compounds containing phos-
phorus and sulfur can be selectively detected by choosing the proper wavelength through the use of
filters (Beroza and Bowman, 1968).
Microcoulometry has also been used as a selective detector for gas-liquid chromatography.
Organic compounds eluting from the column are combusted under oxidative or reductive conditions
to inorganic fragments, which then enter a halogen cell, a sulfur cell, or a nitrogen cell for quantita-
tion. Interposition of suitable scrubbers between the combustion unit and the cells imparts greater
specificity to these detectors. In many cases these detectors are the only ones that will provide the
analyst with an answer for samples with abnormally high backgrounds. The chief problems asso-
ciated with microcoulometric detectors are those of maintenance, inadequate sensitivity, and
stability.
The electrolytic conductivity detector is used for compounds containing halogens, sulfur, or
nitrogen (Coulson, 1966). As in the microcoulometric system, the compounds must be combusted
before entering the detector. Scrubbers between the combustion unit and the detector are also
necessary to make the detector specific for nitrogen compounds. The detector does offer stability
and sufficient sensitivity for residue work.
A gas-liquid chromatograph interfaced with a mass spectrometer as the detector provides a
very powerful tool for analysis. The success of this interfacing has been a major achievement
because the residue must be separated from a large volume of carrier gas. Of all detectors, this one
alone may provide sufficient proof to establish the nature of the residue. It is especially useful for
identifying pesticide metabolites and alteration products. Cost is still a major barrier, and mainte-
nance is a problem.
In instances in which gas-liquid chromatography cannot be used, colorimetric methods have
been successfully applied. The general availability of spectrophotometers enables these methods to
be used in most laboratories. Spectrophotometric methods using ultraviolet or infrared have been
used mostly in formulation analysis. For residue work, such techniques have been hampered by
lack of sensitivity, although micro infrared techniques have been used for qualitative purposes.
The use of colorimetric procedures in monitoring programs presents problems of specificity
and sensitivity. These procedures are based on the reaction of a functional group in the molecule.
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If several herbicides share an identical functional group, all will respond alike. This problem can be
minimized if agreement can be reached that the resultant absorbance readings can be reported as a
function of a single herbicide. In the case of diuron, a substituted urea herbicide, it has been shown
that residues consist of diuron plus several metabolites. The moiety 3,4-dichloroaniline is common
to diuron and its metabolites. It can be determined colorimetrically after diazotization and conju-
gation with an appropriate nucleophilic reagent. The amount of 3,4-dichloroaniline found is then
calculated in terms of diuron.
Such a method cannot be used to monitor samples because 3,4-dichloroaniline is a moiety
common to several urea herbicides, carbamate herbicides, and fungicides. This illustrates the need
for a more specific method. An acceptable solution would be to use the colorimetric method for
quantitative purposes and to use another method to identify the residue. This is feasible if only one
herbicide is present, not a mixture.
Other instrumental methods, such as polarography or atomic absorption, have not been used
extensively in herbicide-residue work. Polarography is a sensitive and specific tool, and it certainly
should be more widely applied. Atomic absorption could be useful for determining arsenical and
mercuric herbicides without regard to their molecular structures.
Specificity and Sensitivity Needs
The specificity of the methods in use today ranges from extremely specific, such as mass spec-
trometry, to quite nonspecific, such as colorimetry. Specificity is a desirable property of any
method, especially in the area of pesticide analysis. Residue work deals with concentrations smaller
than parts per million, and it is imperative that we be certain of our findings so that we can accu-
rately report the identity and quantity of the residue. A method that is specific enables the analyst
to say with complete confidence that the residue found could only be one particular compound.
Most methods do not achieve this degree of confidence because of certain limitations in their means
of detection. Halogen detectors are applicable to many herbicides with a little interference from
natural contaminants. We are thus faced with a dilemma. On the one hand, we want a method that
is applicable to a wide range of herbicides, but, on the other hand, the method should also be
specific.
Tolerances are established on foods and water to ensure the safety of these products for con-
sumption. Tolerance levels of 0.05 ppm are commonly promulgated. To detect such low levels of
residues, sensitive methods must be devised. Through improvements in technology, the sensitivity
of analytical methods is increasing, so that what once was considered a zero residue is now recog-
nized as a finite one. Where formerly we would report zero residues, we can now find traces of a
herbicide. At this stage we must fully evaluate the significance of these ultralow residues and decide
whether we should strive for still greater sensitivity or cease further efforts in this direction and
devote our energies toward trying to make the methods more specific.
Confirmation and Methodology
A peak on a gas chromatogram, a spot on a thin-layer-chromatography plate, or a positive
color reaction does not guarantee the presence of herbicide residue. It is especially important in
cases of samples with unknown spray history that a suspected residue be confirmed by other
means. Confirmation at the residue level can be as difficult as the determination itself. Further
cleanup of the sample may be necessary for some confirmatory methods.
An excellent means of confirmation is to analyze the sample by another procedure completely
different in principle from the first. If the same results are obtained by the second method, con-
firmation has been achieved. This means of confirmation is the primary one if sufficient time and
manpower are available.
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If time and manpower are limited, other methods that do not require the extraction of a dupli-
cate sample may be used. Pyrolytic gas-liquid chromatography is a relatively new technique, and
instrumentation has recently appeared on the market to exploit its usefulness. This type of chroma-
tography depends on the pyrolysis of the pesticide under strictly controlled conditions to produce a
unique series of compounds, which are then chromatographed to obtain a pattern. Ideally, each
pesticide will produce a unique pattern for unequivocal identification. Pyrolytic conditions can be
adjusted toward this goal.
In the case of many pesticides, P-values may be used for qualitative identification (Beroza and
Bowman, 1965; Bowman and Beroza, 1965). Because a P-value represents the distribution of a
herbicide between two immiscible phases, several values can be obtained on a single compound by
using a series of solvent pairs. By comparing the residue's P-values with those of a standard, an
analyst can be quite accurate in identifying the residue. The presence of extraneous matter does
not seem to alter the P-values too drastically from those obtained with a standard. This technique
can only be as accurate as the method used for measuring concentrations of the pesticide in one
phase of the solvent pair.
Derivatization is a technique used to convert one compound into another for ease of deter-
mination or detection. The phenoxyacid herbicides are usually converted to volatile methyl esters
for determination by gas-liquid chromatography. The identity of these herbicides has been con-
firmed by a transesterification procedure in which the methyl esters are converted to corresponding
n-propyl esters and rechromatographed (Yip, 1971); the recorder shows the disappearance of the
methyl ester peak and the appearance of a new peak for the propyl ester.
Derivatives of aromatic-amine-based herbicides are prepared after a hydrolysis step to liberate
the amine. The amine is diazotized and complexed; the different amines form azobenzenes having
characteristic colors. This reaction has been used extensively in detecting substituted urea herbi-
cides on thin-layer plates (Onley and Yip, 1969).
Thin-layer chromatography, like gas-liquid chromatography, has been used for several pur-
poses: cleanup of samples, estimation of residue concentrations, and identification of compounds
by their Rf values. The cleanup of samples is particularly important because extraneous material
tends to impede the mobility of compounds. Too much material can result in streaks that mask the
presence of the herbicide. In lieu of additional cleanup, it may be possible to use another thin-layer
system that can give the desired separation. Another possibility is to chromatograph the sample,
scrape off the area corresponding to the Rf value of the herbicide, and then rechromatograph it on
another plate.
In the analysis of samples, the residue concentration can be estimated by comparing the den-
sity of the residue spot with that of standard spots. This requires the application of several levels of
the standard herbicide to the thin-layer plate along with the sample in order to obtain a range of
densities. The technique is only semiquantitative, but it may be sufficient to indicate whether a
sample meets the tolerance level or to indicate absence of residue.
The Rf values are used to identify compounds on thin-layer plates. Additional specificity can
be gained by using specific colorimetric methods for detecting the compounds on the thin-layer
plate. This technique can provide both Rf and colorimetric reaction criteria for identification.
Two-dimensional thin-layer chromatography can also be used for identification. First the plate
is developed in one direction; after drying, it is turned 90 degrees and developed again with a differ-
ent solvent. Very uniform plates are required for this technique because otherwise solvent fronts
will not be straight. Only one sample can be analyzed on a plate.
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Retention times on two different gas-liquid-chromatography columns have been used as suffi-
cient evidence for confirmation of a residue. The analyst should not depend on this method of
confirmation as final. A better procedure is to use a different detector on the second gas chromato-
graph, preferably one that is more specific. This has been done with the herbicidal carbamates:
compounds containing nitrogen were confirmed by the flame-thermionic detector, compounds con-
taining sulfur by the flame-photometric detector, and halogenated compounds by electron capture
(Onley and Yip, 1971).
Current Outlook
One of the biggest problems in pesticide-residue analysis is the inability of laboratories to con-
firm each other's results. Although the methods are designed to detect extremely minute quan-
tities, in view of the type of sophisticated instrumentation that is available reproducibility between
laboratories leaves much to be desired. Procedures published in the literature often do not provide
enough details to allow a reader to execute the procedure with comparable results. Validated
methods should be available and used if reliable data are to be obtained.
To increase reproducibility between laboratories, a quality-assurance program should be imple-
mented among participating laboratories. A sample fortified with a known pesticide should be sent
periodically to each laboratory to be analyzed as a regular pesticide sample. Results and all the raw
data should be collected and evaluated. Laboratories not meeting the analytical requirements
should be notified, and corrective action should be taken.
Our present capability for measuring residues in soil, water, plants, and air cannot be stated
simply, because many factors enter into the final result. Sensitivity depends on the method of
detection, the compound being measured, and the complexity of the sample containing the residue.
If the analyst knows which herbicide to isolate and measure, his capability for measuring residues
increases manyfold. In general, we can reliably measure 1 ppb in water, 0.1 ppm in soil and foods,
and 0.1 /ig/ft3 of air.
Gas chromatography has afforded the chemist a most sensitive means of making an analytical
determination. Under the proper conditions, picogram amounts can be measured. In providing this
extreme sensitivity, gas chromatography also generated new problems. Solvents and reagents used
in the analytical procedures must be ultrapure in order not to introduce materials that will cause a
detector response. Entire new industries have arisen just for the purpose of purifying solvents for
pesticide-residue analysis. A reagent blank should be obtained as a check on the reagents for each
procedure that is used in the laboratory. This step alone can sometimes save a laboratory from
reporting erroneous results.
Monitoring programs have been and are still being conducted by federal and state organiza-
tions. In these programs, pesticide contents in foods, in the environment, in wildlife, and in humans
are determined periodically. Residues of chlorinated and organophosphorus insecticides are usually
reported because methods of analysis are generally available. The herbicides included in these pro-
grams have been limited to the more widely used chlorophenoxy acids. Except for a few other
individual herbicides, residue data for this class of pesticides in the monitoring programs have been
minimal. It is hoped that more data will be forthcoming as additional herbicide-multiresidue
methods are developed and put to use.
For the future, automation of analysis should provide an impetus for the accumulation
of residue data. Thin-layer chromatography has been automated, and several automatic gas-
chromatographic units are already on the market. Automatic sampling and extracting instruments
are also available. Through additional refinements, it should not be too long before residue analysis
becomes completely automated.
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Liquid chromatography is the latest technique that has been introduced to analytical labora-
tories. The method provides rapid sample cleanup, as well as separation of similar types of com-
pound, by using high-pressure systems. Major emphasis is being placed on devising resins suitable
for high-pressure work. Applications of this technique to herbicide programs will increase as more
instruments become available and successful results are obtained. Cleanup of samples remains the
biggest problem in residue analysis, and if liquid chromatography can help solve this problem, its
use will be adopted.
Analysis for herbicide residues is a difficult task because of the nature of these compounds.
Although residues are not expected to be found from a majority of the registered uses of herbicides,
there should be some data to show complete absence or presence at less than the tolerance level of
any residue in soil, food, water, and air. Until we do have such information, we should not relax
our efforts to obtain it.
REFERENCES
Baunok, I., and Geissbuehler, H., 1968. Bull. Environ. Contam. Toxicol., 3, 7.
Beroza, M., and Bowman, M. C., 1965. Anal. Chem., 37, 291.
Beroza, M., and Bowman, M. C., 1968. Environ. Sci. Technol, 2, 450.
Bowman, M. C., and Beroza, M., 1965. JAOAC, 48, 943.
Coulson, D. M., 1966. Adv. Chromatogr., 3, 197.
Dalton, R. L., and Pease, H. L., 1962. JAOAC, 45, 377.
Devine, J. M., and Zweig, G., 1969. JAOAC, 52, 187.
Gesser, H. D., Chow, A., Davis, F: C., Uthe, J. ¥., and Reinke, J., 1972. Anal. Letters, 4, 883.
Ives, N. P., and Giuffrida, L., 1967. JAOAC, 50, 1.
Katz, S. E., 1966. JAOAC, 48, 452.
McKone, C. E., 1969. J. Chromatogr., 44, 60.
Onley, J. H., and Yip, G., 1969. JAOAC, 52, 526, 545.
Onley, J. H., and Yip, G., 1971. JAOAC, 54, 1366.
Tindle, R. C., Gehrke, C. W., and Aue, W. A., 1968. JAOAC, 51, 682.
Uthe, J. F., Reinke, J., and Gesser, H., 1972. Environ. Letters, 3, 117.
Yip, G., 1971. JAOAC, 54, 343.
Yip, G., 1971. JAOAC, 54, 966.
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ENVIRONMENTAL EFFECTS
FINDINGS
An ample food supply and a viable environmental life system are both necessary for human
survival. Man manages his environment for food production. Herbicides are one of the management
tools that bring about significant, intended environmental effects. The purpose of this analysis is to
investigate and evaluate the unintentional ecological effects that may result from herbicide use. It is
important for man to know how herbicide use affects his environmental life system because man
depends on the immense variety of species in the life system for maintenance of a quality atmos-
phere, for pollination, as well as for the biological degradation of pollution wastes.
After careful consideration of the available evidence, the following are our principal findings:
1. Herbicide-treated areas in the United States represent about 6 percent of the total land
area. Of the total of nearly 500 million pounds of herbicides applied in the United States, 85.2
percent is applied to crop areas, 14.6 percent to rights-of-way and similar brush and tree areas, and
0.2 percent in aquatic locations.
2. Herbicides increase the yields of crops, and this benefits our environment by releasing some
land from cropping. As much as 2.3 million cropland acres may be released from crop production
because of herbicide use to control weeds.
3. Some lakes and pond environments used for recreation may benefit from the use of herbi-
cides to control aquatic weeds.
4. Herbicides have been used effectively in some cases to improve habitats. Herbicides are
sometimes used in terrestrial habitats to increase the food-carrying capacity for individual game
species such as deer and grouse. Herbicides have also been used to improve some aquatic habitats for
certain game birds and fish.
5. The prime sources of herbicide pollution are drift during application and volatilization and
runoff after application. A significant portion of all agricultural herbicides are applied from aircraft.
Of major concern is the fact that as much as 70 to 75 percent of the spray dispersed by aircraft
under adverse conditions may never reach the target weeds. In addition, after application some
herbicides vaporize rapidly and may drift and damage sensitive nontarget plants in the near vicinity.
6. Residues of the herbicides reviewed do not seem to build up in the air, water, and soil en-
vironments. Fortunately, the chemical and physical characteristics of herbicides cause most of them
to degrade within about 3 months. A few herbicides bioconcentrate in aquatic organisms, but the
concentration is seldom more than tenfold. Levels in warm-blooded animals are usually below de-
tectable limits.
7. Herbicides may cause physiological changes in plants, which in turn could upset the ecologi-
cal relationships between these plants and animals associated with them. Several herbicides increase
toxic substances, such as potassium nitrate, produced by plants, making the plants poisonous to ani-
mals ingesting them. Also, herbicides can alter nutritive constituents of plants such as proteins and
vitamins. The limited data available suggest that such changes have produced only minor problems.
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8. Outbreaks of new pests may occur on crops treated with herbicides, thus requiring the use
of additional pesticides. Pathogen and insect pest problems caused by herbicides appear to be rela-
tively infrequent; however, little study has been made of the problem. Some pests have been found
to have increased growth and reproduction on crop plants treated with herbicides. In addition, some
beneficial predaceous insects are destroyed by herbicides, and once this natural control is removed,
the pest insects increase. After herbicide treatments, the physiology of some crop plants has
changed, lowering the level of resistance to pathogen and insect pest attack.
9. Predicting the impact of herbicides on a particular species is difficult because organisms
differ in their sensitivity to herbicides. Present data concerning the toxic effects of herbicides on
plant and animal species and ecosystems are insufficient to predict the changes that will occur in
natural ecosystems. With current use patterns, most herbicides degrade rapidly, with little or no
bioconcentration in the life system. Hence, on the basis of limited data, herbicide impact on natural
ecosystems appears minor.
10. Little information is available concerning low-level, long-term, chronic effects of herbi-
cides on nontarget species.
11. Although effective mechanical controls can be substituted for herbicides in weed manage-
ment for many crops, herbicides are essential for the commercial production of some crops. Weeds
in most situations can be effectively controlled by mechanical cultivation; however, mechanical
control may be more time consuming and costly, and hand labor is often unavailable.
12. The use of herbicides for weed control in crops is sometimes not economically justified.
Using corn as an example and depending on the weather, weeds, and labor availability, economic
returns may be highest from the use of herbicides, from mechanical cultivation, or from a combina-
tion for weed control. Often a combination of weed controls gives the best economic returns.
13. The use of herbicides in some crops may interfere with normal crop rotation, resulting in
increase in pest weeds, insects, and pathogens that may require additional pesticides for control. On
some crops like corn, a herbicide like atrazine may persist from one growing season to another and
prevent the culture of another crop (e.g., soybeans) that is sensitive to this herbicide. Growing corn
continuously year after year may increase some pest weeds, insects, and disease pathogens.
14. The price support and land retirement programs encouraged intensive agriculture which
may include using herbicides as well as other pesticides because increased yields were needed on the
restricted acreages.
15. In some right-of-way areas, herbicides permit selective vegetation management not other-
wise possible. In extensive areas of rough terrain the aerial application of herbicides provides the
only practical method of brush control. Contamination of nontarget areas may occur because
rights-of-way are only a few hundred feet wide and extend for many miles through vast wild habi-
tats. Overall, however, the problem of pollution appears to be minor because applications are in-
frequent and closely regulated.
16. The control of aquatic plants by herbicides is difficult to manage, and it is even more diffi-
cult to assess the ecological impact of control. The reasons for the difficulties in aquatic systems are
(1) natural waters constitute an active transport system for the movement of herbicides out of the
target area; (2) lakes, rivers, and estuaries are complex ecological systems, which make understand-
ing the changes caused by herbicides most difficult.
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17. The costs, benefits, and risks to man and his environment in using herbicides are most
complex; however, in comparison with insecticides, herbicides are generally a smaller environmental
hazard.
INTRODUCTION
Man's management of his environment for crop production has come into conflict with the
preservation of the life system. The effects of this management are not always immediately
apparent, and short-term gains tend to be more heavily weighted than long-term losses. Herbicides
are an important management tool whose intended effects in plant control represent a significant
environmental impact. The purpose of this chapter is not to evaluate the wisdom of the manage-
ment—the intended effects—but to call attention to the unintended effects that may occur as a re-
sult of this particular form of management.
The environmental life system, consisting of an estimated 200,000 species of plants and
animals in the United States, is in a vulnerable status. We appear to have reached a crucial stage
where the continued increased usage of chemicals for a variety of agricultural and nonagricultural
purposes may cause irreversible damage to some essential parts of this life system. Unfortunately,
no one knows how far the environment may be allowed to deteriorate or how many species of
plants and animals can be exterminated before man himself is in serious jeopardy.
The immense variety of species in the life system results from the inherent design in both the
structure and the function of plants and animals. Each has been specifically structured through
evolution to function in a certain way in its particular environment. Thus some species are cold
hardy, some tolerate dry conditions, some require an alkaline-sandy soil, some need light, some
need vitamin Bt 2, and so forth. From the bacterium to the moose, some of the survival require-
ments for each kind of animal and plant are unique.
Man depends on a great variety of species for the maintenance of a quality atmosphere, for an
adequate food supply, and for the biological degradation of wastes. In the presence of sunlight,
plants take in carbon dioxide and water, and release oxygen, which is needed by man and other
animals. The oxygen also yields ozone, which screens out lethal solar ultraviolet rays from the
earth's surface. In addition, the plants are food for many animals, passing their life-making elements
(carbon, oxygen, hydrogen, nitrogen, and others) to the animals in the food chain. Eventually,
microorganisms feeding on wastes and dead animals and plants release vital elements for reuse by
the plants. In this way countless species of the life system interact and function to keep the life-
making elements recycling in the environment. Thus man depends on the other species of the life
system, and, indeed, plants, man, and other animals are all functioning parts of the same "establish-
ment."
Now, when quantities of pollutants are increasing, species populations of the life system serve
another valuable role: as "indicators" of when pollutant dosages are reaching dangerous levels in
the environment. If we acknowledge the contribution all species make in keeping the life system
functioning and in indicating danger, we must recognize that man's welfare is threatened when
chemical pollutants, including herbicides, affect other species of the environmental life system. In
general, chemical pollutants as well as nonchemical manipulations, such as the construction of
roads and channels, may have a disruptive and deleterious impact on life systems (PSAC, 1965).
The impact of chemical pollutants on life systems includes the following:
1. The number of species constituting a life system is often reduced after exposure to chemical
pollutants.
2. Significant reductions in the number of species may lead to instability within a life system
and subsequently to population outbreaks of some species because the normal check-balance
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structure of the system is altered. For example, when a species of predator, parasite, or competitor
that limits the increase of another species is reduced, the population once held in check may
increase explosively.
3. After the disappearance of a pollutant from the affected area, populations eventually
regain their balance. For a time, however, those species populations low in the food chain (e.g.,
the herbivorous animals or plant feeders) are usually the ones to increase to outbreak levels. This
often results in a serious disruption of the ecosystem in the affected area.
4. Predator and parasite species high in the food chain are quite susceptible both to the loss
of a species and to extreme population fluctuations of species low in the food chain on which they
depend. Thus, when a species low in the food chain is affected, the many dependent species also
suffer, and the check-balance mechanism is made more uncertain.
In the United States during 1971 about 353 million pounds of herbicides were aimed at
several hundred weed species (USDA, 1973). In the process the populations of many nontarget
plant and animal species in the environmental life system were directly or indirectly affected by the
herbicides.
This chapter briefly evaluates the available evidence concerning the environmental impact of
herbicide use. Particular attention is focused on residues in air, water, soil, and organisms, as well
as environmental effects related to crop, aquatic, industrial, and conservation uses. Emphasis is
placed not only on the identification of ecological consequences but also on possible alternatives
and less hazardous usage of herbicides.
SOURCES AND MOVEMENT OF HERBICIDES IN THE ENVIRONMENT
The environmental contamination of target and nontarget areas depends on (1) toxicity of
herbicide, (2) biomagnification, (3) persistence, (4) amount used, (5) application method, and
(6) movement. Although the toxicity of herbicides to animals varies widely, herbicides as a class
are less toxic than insecticides. Biomagnification occurs primarily in plants, which can be a hazard,
but seldom in animals. Persistence increases the chances of a herbicide's becoming a pollutant.
This is because the longer a material remains in the environment, the greater the opportunity for
the chemical to be a problem within the target area or to move out of the treated area and become
a hazard elsewhere.
In terms of the amount used, the pollution problem is clear and needs no explanation. Appli-
cation methods determine the amount of herbicide used and the extent of environmental contami-
nation. Of major concern is the extensive use of aerial application: 15 to 20 percent of all
agricultural herbicides is applied by aircraft (USDA, 1972). Akesson and Yates (1971) report
that spray recoveries from aircraft applications may be as low as 25 to 30 percent of the amount
applied. Widespread drift effects from aircraft applications have occurred, for example, in
California. Propanil was applied to rice and injury to fruit trees was observed about 55 miles
downwind (Akesson, 1971).
Airborne concentrations harmful to nontarget crops are most frequently due to drift at the
time of application of the herbicide to the target. Usually residues on plants contaminated from
drift are far lower than those on the target species of plants; however, sensitive plants, such as
cotton and grapes, are particularly vulnerable to 2,4-D and, under rare weather circumstances, may
be damaged by residues as much as 15 miles from the point of application. However, damage most
frequently occurs within 500 feet (Van Middelem, 1966).
48
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Herbicide residues due to drift are most closely correlated with the type of equipment used,
herbicide formulation, and wind velocity. Most serious drift problems can be solved by modifying
equipment; using such formulations as granules, inverted emulsions, and spray thickeners; and
avoiding small particulates and windy days for application (Butler et al., 1969; Akesson et al, 1971;
Akesson et al, 1972). Particles of soil, spray droplets, and rain droplets that can be carried by
normal wind velocities of 5 mph for over 100 feet vary from less than 5 to 100 microns in diameter
(Reimer et al., 1966). Assuming particles to have nearly equal deposition of the herbicide on
treated soil, particles 10 microns in diameter will have a surface area 1000 times as great per volume
as particles 100 microns in diameter and consequently about 100 times the residue in parts per
million, assuming no volatility.
The operational techniques utilized to apply the spray and the microclimate at the time of
application are also important variables that affect drift. Climatic inversion conditions, not infre-
quent in parts of the United States, can result in a particularly acute drift problem because the
movement of the spray (especially small particles) is concentrated near ground level in a horizontal
direction—often far from the target area. Applying herbicides with winds of 10 mph or greater
generally causes the most problems with herbicide drift.
Herbicides move from treated land areas primarily via vaporization and also by rain and
irrigation water. For example, both 2,4-D esters and EPTC vaporize rapidly and may affect
nontarget plants in the near vicinity. The use of 2,4-D near certain crops has been restricted in some
states (e.g., California and Texas) to prevent damage to highly sensitive crops. Most of the herbi-
cides mentioned in Table 1 are more soluble in water than are insecticides. Although soluble and
susceptible to leaching, the amounts found in water outside the target area are small (White et al.,
1967; Axe et al., 1969). The relative mobility of pesticides in soil leaching experiments show
phenoxy and picloram herbicides to be most mobile, followed by a group of miscellaneous herbi-
cides, then by phenylureas, triazines, and other related herbicides, and then by CIPC and toluidine
herbicides (Norris and Moore, 1970). Herbicides, however, in runoff soil and water from certain
treated areas such as crops and roadsides may result in some pollution problems.
Various agents are added to certain herbicide formulations to increase their efficiency of
contact with the plant surface and their duration of contact. These additives include oil emulsifiers
as well as thickeners (cellulose, alginates, swellable polymers) and foam additives. These additives
may also result in coarser sprays and hence a reduction of drift. Viscosity additives have been used
particularly for industrial applications. Thus any consideration of the environmental impact of
herbicides must also consider the action and fate of additives (as well as impurities, as occurred
with 2,4,5-T). For example, although certain additives may result in a drift reduction, they can
also retard herbicide degradation rates (Akesson and Yates, 1971). Furthermore, such carriers as
diesel oil, which is used commonly in forestry practices, may constitute 80 to 90 percent of the
spray solution (Tarrant and Norris, 1967).
Once a herbicide has been directed at a target system, what happens to it? As stated earlier,
depending on application procedures, a portion of the herbicide may never hit the target, but
rather disperse by drift. That which does hit the target may be lost from it through a variety of
routes, including runoff, erosion, leaching, and volatilization, or perhaps even through migration
of the biota (Figure 1).
Within the target system, the breakdown of herbicides is generally fairly rapid, either within
the soil system or in the above-ground food chain. The herbicide is largely deactivated in the plant,
although it can be lost from the plant by a variety of routes, including exudation by roots into the
rhizosphere (Reid and Hurtt, 1970), where it may be broken down. There does not appear to be
bioconcentration of herbicides in higher trophic levels. The flesh of deer that had eaten vegetation
treated with 2,4,5-T or atrazine rarely had detectable residues (Newton and Norris, 1968). Even in
soils of rangeland treated with the relatively persistent picloram, this agent usually totally dissipates
within a year (Scifres et al., 1971).
49
-------
Table 1. TOXICITY OF HERBICIDES TO MAMMALS, BIRDS, FISH,
AND INVERTEBRATES
Common name
(trade name)
of herbicide
Acrolein (Aqualin,
Hydrotfial)
Alachlor (Lasso)
Atrazine
Butylate (Sutan)
Name of organism
Rat
Rabbit
Rat
Bluegill
Chinook salmon
Coho salmon
Rainbow trout
Largemouth bass
Mosquito fish
Fathead minnow
Bluegill
Brown trout
Rat
Pheasant
Rainbow trout
Bluegill
Rat
Mouse
Rat
Cattle
Sheep
Bobwhite
Mallard
Japanese quail
Ring-necked pheas-
ant
Chicken
Spot
Harlequin fish
Rainbow trout
Bluegill
E. Oyster
Brown shrimp
Water flea (Daphnia
magna)
Rat
Guinea pig
Rat
Dog
Bobwhite
Bluegill
Rainbow trout
Gammarus fasciatus
Type of test
exposure
Acute oral
Acute oral
Water dietary, 90-
day
Acute, 96-hr
Acute, 24-hr
Acute, 0.25-hr
Acute, 24-hr
Acute, 96-hr
Acute, 48-hr
Acute, 48-hr
Acute,1 24-hr
Acute,1 24-hr
Acute oral
Dietary, 90-day
Dietary, 5-day?
Acute, 96-hr
Acute, 96-hr
Acute oral
Acute oral
Dietary, 2-yr
Acute oral
2 CDOD4
10 CDOD4
Acute oral
3 CDOD4
8 CDOD4
Dietary, 5-day
Dietary, 5-day
Dietary, 5-day
Dietary, 5-day
10 CDOD4
10 CDOD4
Acute, 48-hr
Acute, 24-hr
Acute, 96-hr
Acute, 48-hr
Acute, 96-hr, ffowmg
seawater
Acute, 48-hr
Acute, 48-hr
Acute oral
Acute oral
Dietary, 90-day
Dietary, 90-day
Dietary, 7-day
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Dosage
46 mg/kg
7 mg/kg
200 ppm
0.1 ppm
0.08 ppm
2.0 ppm
0.14 ppm
0.16 ppm
0.06 ppm
0.01 5 ppm
0.079 ppm
0.046 ppm
774 mg/kg2
200 ppm
>4300 ppm
1.0 ppm2
5.8 ppm2
3080 mg/kg
1750 mg/kg
100 ppm
50 mg/kg
25 mg/kg
10 mg/kg
100 mg/kg
50 mg/kg
25 mg/kg
>5000 ppm
>5000 ppm
>5000 ppm
>5000 ppm
50 mg/kg
25 mg/kg
1 ppm
0.55 ppm
4.5 ppm
26 ppm
1 ppm
1 ppm
3.6 ppm
4659-5431 mg/kg
1659 mg/kg
32 mg/kg-day
40 mg/kg-day
40,000 ppm
6.9 ppm
4.2 ppm
10.0 ppm
Effect
LDSO
LD50
No effect
LCso
LC50
100% mortality
LCSO
LCSO
LCso
LC50
LCso
LCSO
LDSO
No effect
LCso
LCso
LCso
LD50
LD50
No effect
Significant effect'
Significant effect3
No effect
Significant affect3
Significant effect9
Significant effect9
LCSO
LCSO
LCso
LCso
Significant effect3
No effect
No mortality
LCSO
LCSO
LC50
No effect
30% mortality or
loss of equilib-
rium
LC50
LD50
LDSO
No effect
No effect
LCSO
LC50
LC50
LCSO
Reference
Anon. (1970)
Lawrence (1963)
Pimentel (1971)
Lawrence (1963)
Battelle (1971)
Anon. (1970)
Anon. (1970)
Palmer and Radeleff
(1969)
Heath eta/. (1972)
Palmer and Radeleff
(1969)
Pimentel (1971)
EPA (1972)
Pimentel (1971)
Pimentel (1971)
Anon. (1970)
Sanders (1970a)
50
-------
Table 1. TOXICITY OF HERBICIDES TO MAMMALS, BIRDS, FISH,
AND INVERTEBRATES-Continued
Common name
(trade name) Name of organism
of herbicide
Chloramben Rat
(Amiben)
Cattle
Sheep
Bobwhite
Chicken
Rainbow trout
Bluegill
Copper sulfate5 Sheep
Mallard
Ring-necked pheas-
ant
Bluegill
Striped bass
Bluegill
Bass
Goldfish
Fathead minnow
Daphnia
Daphnia
2,4-D (acid)' Rat
Mouse
Rabbit
Oog
Guinea pig
Mule deer
Rat
Dog
Rat
Cattle
Sheep
Mallard
Ring-necked pheas-
ant
Japanese quail
Pigeon
Chicken
Chorus frog tadpole
Bluegill
Rainbow trout
Daphnia magna
Gammarus fasciatus
Type of test
exposure
Acute oral
Dietary, 2-yr
10 CDOD4
10CDOD4
2 CDOD4
10CDOD4
Acute oral
7 CDOD4
10 CDOD4
10 CDOD4
Acute, 96-hr
Acute, 96-hr
Dietary
Acute oral
Acute oral
Acute, 24-hr
Acute, 48-hr
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 16-hr
Acute, 2-hr
Acute oral
Acute oral
Acute oral
Acute oral
Acute oral
Acute oral
Dietary, 2-yr
Dietary, 2-yr
Three-generation re-
production
Acute oral
25 CDOD4
86 CDOD4
112 CDOD4
7 CDOD4
10 CDOD4
8 CDOD4
Acute oral
Dietary, 5-day
Acute oral
Dietary, 5-day
Acute oral
Dietary, 5-day
Acute oral
10 CDOD4
10 CDOD4
10 CDOD4
Acute, 24-hr
Acute, 24-hr
Acute, 24-hr
Acute, 48-hr
Acute, 48-hr
Dosage
5620 mg/kg
1 0,000 ppm
250 mg/kg
175 mg/kg
50 mg/kg
25 mg/kg
>700 mg/kg
500 mg/kg
375 mg/kg
250 mg/kg
4.2 ppm
1000 ppm
25 mg/day
>2000 mg/kg6
>2000 mg/kg6
1.5 ppm
0.15 ppm
3.0 ppm
3.0 ppm
1.0 ppm
1.0 ppm
0.1 ppm
100 ppm
666 mg/kg
375 mg/kg
800 mg/kg
100 mg/kg
1000 mg/kg
400-800 mg/kg
1250 ppm
500 ppm
500 ppm
250 mg/kg'
200 mg/kg9
100 mg/kg9
50 mg/kg9
500 mg/kg9
250 mg/kg9
100 mg/kg9
> 1000 mg/kg
>5000 ppm8
472 mg/kg
> 5000 ppm8
668 mg/kg
>5000 ppm8
668 mg/kg
500 mg/kg9
250 mg/kg9
100 mg/kg9
100 ppm
5 ppm
5 ppm
> 100 ppm
3.2 ppm
Effect
LDSO
No effect
Significant effect3
No effect
Significant effect3
No effect
LD50
Significant effect3
Significant effect3
No effect
LCSO
LCSO
Jaundice
LDSO
LDSO
LC50
LCSO
Tolerated
Tolerated
Tolerated
Tolerated
ECSO'
100% mortality
LD!0
LD50
LD50
LD50
LDSO
LDSO
No effect
No effect
No effect
Significant effect3
Significant effect3
Significant effect3
No effect
Significant effect3
Significant effect3
No effect
LD50
LC50
LD50
L-C5o
LD50
LC50
LD50
Significant effect3
Significant effect3
No effect
LC50
No mortality
No mortality
LC50
LC50
Reference
Anon. (1970)
Palmer (1972)
EPA (1972)
Palmer (1972)
EPA (1972)
Pimentel (1971)
Lawrence (1962)
Pimentel (1971)
Hansen etal. (1971)
Palmer (1972)
Pimentel (1971)
Palmer (1972)
Pimentel (1971)
Applegate ef a/.
(1957)
Sanders (1970a)
51
-------
Table 1. TOXICITY OF HERBICIDES TO MAMMALS, BIRDS, FISH,
AND INVERTEBRATES-Continued
Common name
(trade name) Name of organism
of herbicide
Diuron (Karmex) Rat
Rat (Low Chronic
Toxicity)
Cattle
Sheep
Bobwhite
Japanese quail
Ring-necked pheas-
ant
Mallard
Chicken
Bullfrog tadpole
Rainbow trout
Coho salmon
Largemouth bass
Bluegill
White crappie
Striped bass
Daphnia pulex
Gammarus
E. Oyster
Brown shrimp
Endothall Rat
Dog
Cattle
Sheep
Chicken
Bluegill
Carp
Largemouth bass
Fathead minnow
Daphnia magna
Gammarus lacustris
Linuron (Lorox) Rat
Dog
Cattle
Sheep
Chicken
Carp
Type of test
exposure
Acute oral
10 CDOD4
10 CDOD4
Acute oral
2 CDOD4
10 CDOD4
Dietary, 5-day
Dietary, 5-day
Dietary, 5-day
Dietary, 5-day
10 CDOD4
10 CDOD4
Acute
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute, 24-hr
Acute, 24-hr
Acute, 96-hr
Acute, 48-hr
Acute, 48-hr
Acute, 96-hr, flowing
saltwater
Acute, 48-hr, flowing
saltwater
Acute oral
Dietary, 2-yr
Dietary, 2-yr
2 CDOD4
10 CDOD4
2 CDOD4
2 CDOD4
10 CDOD4
10 CDOD4
10 CDOD4
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 24-hr?
Acute, 24-hr
Acute oral
Acute oral
Acute oral
6 CDOD4
10 CDOD4
10 CDOD4
4 CDOD4
1 CDOD4
10 CDOD4
10 CDOD4
Acute, 48-hr
Dosage
3400 mg/kg
100mg/kg
50 mg/kg
250 mg/kg
100 mg/kg
50 mg/kg
1730ppm
>5000 ppm
>5000 ppm
>5000 ppm
10 mg/kg
5 mg/kg
10 ppm
4.3 ppm
42 ppm
16 ppm
9.7-27 ppm10
8.75 ppm
3.1 ppm
1.4 ppm
0.38 ppm
1.8 ppm
1 .0 ppm
38-51 mg/kg
>300ppmn
>300ppm"
25 mg/kg12
10 mg/kg12
50 mg/kg12
25 mg/kg12
10 mg/kg12
5 mg/kg12
10 mg/kg12
125 ppm13
175 ppm"
120-200 ppm13
320-6 10 ppm13
46 ppm
2 ppm
1500 mg/kg
4000 mg/kg
500 mg/kg
100 mg/kg
50 mg/kg
25 mg/kg
100 mg/kg
50 mg/kg
25 mg/kg
10 mg/kg
>10ppm
Effect
LDSO
Significant effect3
No effect
Significant effect3
Significant effect3
No effect
LCSO
LC50
LCso
LC50
Significant effect3
No effect
100% mortality
LC50
LCSO
LC50
LCSO
50% mortality
LC50
LCSO
LC50
Shell growth de-
creased
No effect
LDSO
No effect
No effect
Significant effect3
No effect
Significant effect3
Significant effect3
Significant effect3
No effect
Significant effect3
LCSO
LCso
LCso
LCso
ECS014
LC50
LDSO
LD50
LDSO
Significant effect3
Significant effect3
No effect
Significant effect3
Significant effect3
No effect
Significant effect3
LC50
Reference
Anon. (1970)
Palmer and Radeleff
(1969)
Heath eta/. (1972)
Palmer and Radeleff
(1969)
Lawrence (1963)
Pimentel (1971)
Battelle (1971)
Anon. (1970)
Palmer (1972)
Pimentel (1971)
Lawrence (1963)
Pimentel (1971)
Sanders (1970a)
Martin (1968)
Palmer and Radeleff
(1969)
EPA (1972)
52
-------
Table 1. TOXICITY OF HERBICIDES TO MAMMALS, BIRDS, FISH,
AND INVERTEBRATES-Continued
Common name
(trade name)
of herbicide
Nitralin (Planavin)
Propachlor (Ramrod)
Propazme (Milogard)
Trifluralin (Treflari)
Name of organism
Rat
Mouse
Rat
Cattle
Sheep
Chicken
Bluegilt
? Trout
Goldfish
Silver salmon
Rat
Cattle
Sheep
Ring-necked pheas-
ant
Chicken
Bluegill
Fathead minnow
Rat
Mouse
Rat
Cattle
Sheep
Bobwhite
Mallard
Chicken
Rainbow trout
Goldfish
Bluegill
Rat
Mouse
Dog
Rabbit
Rat
Dog
Cattle
Type of test
exposure
Acute oral
Acute oral
Dietary, 2-yr
2 CDOD4
10CDOD4
4 CDOD4
10 CDOD4
Acute oral
10 CDOD4
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute oral
Dietary, 90-day
3 CDOD4
10 CDOD4
4 CDOD4
9 CDOD4
10 CDOD4
Acute oral
3 CDOD4
10 CDOD4
10 CDOD4
Acute, 96-hr
Acute, 96-hr
Acute oral
Acute oral
130 CDOD4
2 CDOD4
3 CDOD4
10 CDOD4
Acute oral
10 CDOD4
5 CDOD4
10 CDOD4
(Low toxicity)
(Low toxicity)
6 CDOD4
10 CDOD4
25 CDOD4
Acute, 96-hr
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute oral
Acute oral
Acute oral
Acute oral
Dietary, 2-yr
Daily, 2-yr
dietary capsule
2 CDOD4
10 CDOD4
Dosage
>2000 mg/kg
>2000 mg/kg
2000 ppm
250 mg/kg
175 mg/kg
500 mg/kg
250 mg/kg
>1 000 mg/kg
500 mg/kg
20 ppm
20 ppm
20 ppm
20 ppm
710 mg/kg
133 mg/kg-day
25 mg/kg
10 mg/kg
50 mg/kg
10 mg/kg
5 mg/kg
735 mg/kg
1000 mg/kg
10 mg/kg
5 mg/kg
1.3 ppm
0.49 ppm
>5000 mg/kg
>5000 mg/kg
250 mg/kg
250 mg/kg
25 mg/kg
10 mg/kg
500 mg/kg
100 mg/kg
25 mg/kg
10 mg/kg
250 mg/kg
100 mg/kg
25 mg/kg
MOO ppm
7. 8 ppm
>32 ppm
>100 ppm
> 10,000 mg/kg
5000 mg/kg
>2000 mg/kg
>2000 mg/kg
>2000 ppm/day
> 1000 ppm
175 mg/kg
100 mg/kg
Effect
LD50
LDSO
No effect?
Significant effect3
No effect
Significant effect3
No effect
LD50
No effect
No mortality
No mortality
No mortality
No mortality
LD50
No effect
Significant effect3
No effect
Significant effect3
Significant effect3
No effect
LDSo
Significant effect3
Significant effect3
No effect
LCso
LC50
LD50
LD50
No effect
Significant effect3
Significant effect3
No effect
Significant effect3
Significant effect3
Significant effect3
No effect
Significant effect3
Significant effect3
No effect
LC50
LC50
LC50
LCSO
LD50
LD50
LDSO
LD50
No effect
No effect
Significant effect3
No effect
Reference
Anon. (1970)
Palmer (1972)
Martin (1968)
Palmer (1972)
Martin (1968)
Anon. (1970)
Palmer (1972)
Anon. (1970)
Palmer (1972)
Anon. (1970)
Anon. (1970)
Palmer and Radeleff
(1969)
Anon. (1970)
Palmer and Radeleff
(1969)
EPA (1972)
Pimentel (1971)
EPA (1972)
Pimentel (1971)
Anon. (1970)
Palmer and Radeleff
(1969)
53
-------
Table 1. TOXICITY OF HERBICIDES TO MAMMALS, BIRDS, FISH,
AND INVERTEBRATES-Continued
Common name
(trade name) Name of organism
of herbicide
Trifluralin (Treflan) Sheep
(continued)
Ring-necked pheas-
ant
Chicken
Mallards
Chicken
Rainbow trout
Fathead minnow
Bluegill
Channel catfish
Goldfish
Daphnia magna
Daphnia pulex
Gammarus lacustris
Gammarus fasciatus
Crayfish
(Orconectes nais)
Xylene Rat
Various species of
fish
Bluegill
Rainbow trout
Sea lamprey
Orange-spotted
sunfish
Daphnia magna
Type of test
exposure
2 CDOD4
10CDOD4
Acute oral
Acute oral
Acute oral
10 CDOD4
10 CDOD4
10 CDOD4
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 96-hr
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute, 48-hr
Acute oral
Acute
Acute, 24-hr
Acute, 24-hr
Acute, 24-hr
Acute, 1-hr
Acute, 48-hr
Dosage
175 mg/kg
100mg/kg
>2000 mg/kg
>2000 mg/kg
>2000 mg/kg
500 mg/kg
250 mg/kg
100 mg/kg
0.01-0.086 ppm
0.093 ppm
0.01 9-0.089 ppm
0.254 ppm
0.252 ppm
0.56 ppm
0.24 ppm
5.6 ppm
1.0 ppm
50.0 ppm
4300 mg/kg
10-90 ppm
5 ppm
5ppm
5 ppm
47 ppm
0.01-0.1 ppm
Effect
Significant effect3
No effect
LDso
LD50
LDSO
Significant effect3
Significant effect3
No effect
LC50
LCSO
LC50
LCSO
LC50
LCSO
LCjo
LC50
LCSO
LCSO
LD5015
Will kill fish16
Sick
No mortality
No mortality
Kill
Kill
Reference
Pimentel (1971)
Palmer and Radeleff
(1969)
EPA (1972)
Battelle (1971)
EPA (1972)
Sanders (1970a)
Pimentel (1971)
Sanders (1970a)
McKee and Wolf
(1971)
Lawrence (1962)
1 Continuous flow.
2 Corrected for 4-lb/gal emulsifiable composition, probably 43 percent a.i.
3Weight loss, reduced weight gain, or illness.
4 CDOD = consecutive daily oral doses each at the given dosage.
5Toxicity varies greatly with pH and turbidity.
6 Bordeaux mixture.
'Dead or immobilized.
"There is very little variation in toxicity among the various salts and esters of 2,4-D in mammals and birds; however, certain
esters are much more toxic than the acid to fish (/\*'\ ppm).
'Alkanolamine salts.
10 Different temperatures.
11 Disodium salt.
12 Potassium salt.
13Cocoamine, dimethylamme, and copper salts may be toxic to fish at less than 1 ppm.
14 Immobilization.
15 Usually a mixture of o-, m-, and p-xylene.
"m-Xylene—usually the most toxic of the isomers.
54
-------
Loss from Target System
Agent Carrier
Drift
Non-Target
System
Leaching
Migration
Wind Erosion
Runoff
Volatilization
Target System
Target Plant
Non-target Plant
Herbivores
Carnivores
Decomposers
Soil
Water
Air
Impurities
Biological and
Physical
Degradation
Figure 1. Potential pathways for the loss of herbicides from target systems
55
-------
RESIDUES OF HERBICIDES
The herbicide-residue level in the environment is related to the dosage applied, the number of
applications, the method of application, the type of herbicide formulation, habitat, wind, sunlight,
oxygen, rain, the soil type (especially to organic matter, clay minerals, pH, temperature), micro-
organisms (aerobic or anaerobic), the time after application, and so forth. Relative levels of these
residues can be predicted with reasonable accuracy from a correlation of the physical, chemical,
and biological properties of the different kinds of herbicides with the above environmental
variables and with herbicide uses and application methods (Freed, 1966; Van Middelem, 1966;
Kenaga, 1968).
The determination of herbicide residues must include the products of molecular transforma-
tions such as hydrolysis, oxidation, and reduction. Also, consideration must be given to the
ingredients of the formulation and the impurities present, whether due to manufacture, packaging,
or storage of the material. One need only study the development of such pesticides as 2,4,5-T
(and its toxic tetrachlorodibenzo-p-dioxin trace impurity) to realize the importance of the above
determinations. In fact, few herbicides have been subjected to detailed analysis for product
impurities at the 1-ppm level.
Reactions associated with the microbial metabolism of herbicides include W-dealkylation of
ureas, ester or amide hydrolysis of carbamates, side-chain degradation of the s-triazines, and
dechlorination of 2,4-D and dalapon (Kearney, 1966). Not all herbicides are metabolized
directly to smaller molecules. For example, propanil converted microbially to 3,4-dichloroaniline
is thought to form a larger molecule by diazotization by the nitrate ion in the soil (Rosen, 1972).
Bioaccumulation of Residues
The use of the terms "bioaccumulation" and "bioconcentration" often conjures up the image
of the type of residue accumulation that occurs with DDT in animal organisms, especially in their
fat tissues. The bioconcentration factor (biomagnification) is the ratio of the measured residue in
an animal or plant (or a specific tissue) to the measured residue in the ambient air, water, or soil
environment of the organism and/or the various species of food organisms consumed, as specified
(Kenaga, 1972). The highest bioconcentration factors with insecticides usually occur in water.
DDT and its degradate DDE may have a bioconcentration factor of a million. Such herbicides as
picloram (Hardy, 1966), Silvex (Getzendaner, 1960), 2,4-D (Cope et al, 1970; Smith and Isom,
1967), and dichlobenil (Cope et al, 1969) do not appear to bioconcentrate in fish or aquatic
organisms more than tenfold and often not at all. Diuron may have a bioconcentration factor of
several hundred (McCraren et al, 1969).
Although oysters and clams may accumulate from 3.6 to 3.8 ppm of 2,4-D in herbicidally
treated areas such as Chesapeake Bay, they cleanse themselves of residues before harvest time
(Frank, 1971). Butler (1965) exposed oysters continuously for 7 days to 0.1 ppm of 2,4-D
butoxyethanol ester. The oysters accumulated 18 ppm and cleansed themselves in 7 days with
fresh seawater. Fish in treated ponds may retain the residues of some herbicides for weeks
(McCraren et al, 1969; Cope et al, 1969).
The important fact concerning chronic toxicity is not how large the bioconcentration factor
is, but how much actual residue (in parts per million) bioaccumulates.
The terms "bioaccumulation" and "bioconcentration" may be applied to plants, but
generally speaking, the properties of a chemical used to penetrate and kill insects are quite different
from those needed to penetrate and kill plants. Among other things, insecticides that are nonsys-
temic poisons are often quite high in fat solubility (in order to penetrate insects) and low in water
solubility. Thus stable compounds may be bioaccumulated in animal fats and be consumed by
56
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other animals. Most herbicides tend to have greater water solubility and/or do not partition
as greatly in favor of fat tissues as do DDT and other organochlorine insecticides. Further
degradation of most herbicides leads to products that are even more water soluble—for example,
atrazine to hydroxyatrazine and prometryne to hydroxypropazine (Shimabukuro and Swanson,
1969; Frans et al., 1972). Many herbicides penetrate plants and are redistributed, especially in the
growing portions of the plants, such as leaves and roots. Because herbicide residues on treated
plant foliage are often determined for the whole leaf, the differences between surface and internal
residue concentration are often not appreciated.
Assuming an even coverage of herbicide on the surface of various plants, the residues vary
greatly in parts-per-million values since the surface-to-volume ratios of the different parts of plants
and different species of plants do vary. In a literature study of many pesticides, the maximum
residues of pesticides were calculated on a 1-lb/acre basis by dividing the residues determined by
analysis by the dosage in pounds per acre applied (Hoerger and Kenaga, 1972). Such maximum
residues, immediately after application, ranged from 6.6 ppm for fruits to 240 ppm for foliage such
as grass, depending on the surface-to-volume ratio (size and shape of vegetation sprayed). The
highest amounts of residues occurred with systemic herbicides and insecticides on foliage. Most
residues were far lower than the maximum residues cited above. All residues declined within days
after application, although some traces persisted for months at levels above the limit of analytical
sensitivity (Hoerger and Kenaga, 1972).
Duggan et al. (1971) reported on pesticide levels in foods and feeds in the United States from
1963 to 1969. The only herbicides found were 2,4-D, MCP, and dacthal. None was found com-
monly or in amounts exceeding parts per billion.
Residues in Soil
A major problem in assaying herbicide residues in soil is the accurate measurement of actual
amounts of the compound and/or its degradation products at varying time periods after application.
Only a few studies include a wide variety of the most commonly used herbicides tested compara-
tively in the field (Table 2). A Southern State Regional Cooperative Study (Frans et al., 1972)
showed that no phytotoxic residues of atrazine, chlorpropham, DCPA, diphenamid, diuron, linuron,
norea, prometryne, or trifluralin persist in soil after 1 year when applied at recommended rates;
however, no analytical residue data accompanied this phytotoxicity data. Herbicide residues are
likely to persist two or more times longer in the colder areas of the United States and Canada. In
Oregon, studies of chemical brush control with 2,4-D, amitrole, 2,4,5-T, and picloram indicated
that detectable residues of picloram persisted for more than a year while the rest degraded more
rapidly (Norris, 1971).
Analytical work shows that, even though phytotoxicity may not occur on the target crop in
soil treated year after year, residues of the herbicide (and degradates) may still be bound to the
soil and may be subject to release under certain circumstance?. The nature and mechanism of the
binding and releasing of pesticide residues held by lignin, humus, cellulose, and other organic
matter is uncertain, and residues may sometimes be a problem in the rotation of crops sensitive to
herbicides.
All compounds leach to some degree. Anderson et al. (1969) discussed the various factors
related to leachability, relating it to soil pH as well as mineral and organic content. Two closely
related compounds, trifluralin and nitralin, vary greatly in leachability. Even mineral soils are
capable of strong adsorption, for example, of phenolic and phenoxyacetic acid herbicides. The
adsorption of such compounds is near a maximum when the calculated ionization is about 15 to
30 percent and when the pH approaches the pKa of the herbicide in water (Miller, 1972).
57
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Table 2. PERSISTENCE OF HERBICIDES IN SOIL IN FIELD TESTS1
Herbicide
Alachlor
Atrazine
Amount applied to soil
(Ib/acre)
1-4
2-4
2-3
3-8
2-4
Residual phytotoxicity
(months)
1.5-2.5
4-72
4-72
122
<12->12
Butylate
Chloramben
2,4-D
3-4
2-4
3-4
0.12-0.753
1.5-2
0.25-1
Diuron2
Endothall
Linuron
Nitratin
Propachlor
Propazine
Trifluralin
3.6-4
1-2
2
0.6-6.4
12
4
0.5-3
0.5-1.5
3-6
1-4
3
1.8
4
0.5-1
5-72
4-82
152
One growing season
12
<42
4
"Moderately persistent"
1-1.5
<12
22
142
52
4-6
1 Unless otherwise indicated, data are from the Herbicide Handbook of the Weed Society of
America (Anon., 1970). Average residual phytotoxic life given for stated dosages, which are the
recommended crop-use dosages.
2 Data from Sheets and Harris (1965).
3 Half-life.
Organic material (principally humus) is the major soil constituent that reduces leaching because
of its strong adsorption. For example, sodium humate apparently adsorbs and solubilizes the non-
polar compound 2,4,5-T from solution (Wershaw et al., 1969). Organic material can adsorb most
organic compounds from water; thus, in practice, phytotoxicity due to leaching is a rare problem
even when water-soluble herbicides are applied to organic soil.
Herbicide (2,4-D) residues in the bottom muds of cold lakes or those with low oxygen
contents may persist for 10 months (Smith and Isom, 1967).
58
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Residues in Water
The herbicides most commonly used to control aquatic weeds are xylene, copper sulfate,
2,4-D, acrolein, endothall, and diuron (Anon., 1971). Few materials are registered for this use
because of the potential environmental problems. The main sources of herbicidal residues in
water are from direct application, aerial drift from application, runoff from land, and control of
ditchbank vegetation (Frank, 1971).
Johnson et al. (1967) discussed the pesticide-residue-monitoring studies carried on by various
U.S. agencies and concluded that a number of insecticides were important residue indicators, but
none of these were herbicides. Eleven streams in the Western United States were monitored for
nine insecticides, 2,4-D, 2,4,5,-T, and Silvex. No herbicide residues were found (Brown and
Nishioka, 1967).
Dosages of most herbicides applied for aquatic weed control are initially on the order 0.1
to 4 ppm in water, except for aromatic solvents (xylene), which are as high as 600 to 700 ppm.
The latter residues, however, are highly volatile and diminish rapidly in water. Residues of many
herbicides are detectable (>0.1 ppm) for days and weeks after application in treated pond water
but rarely exceed 0.5 ppm after a few days (Frank, 1971, Table 4). Fenac, 3-aminotriazole, and
dichlobenil appear to be the most persistent (Grzenda et al., 1966; Van Valin, 1966). Herbicide
concentrations in excess of 0.1 ppm are seldom encountered in forest streams close to treatment
areas, even immediately after spraying (Norris, 1971).
The determination of the half-life, or "disappearance rate," of herbicide residues in water
varies considerably, depending on temperature, ultraviolet light, pH of the water, aeration, size
and nature of the particulate matter in the water, amount of vegetation in water, surface-depth
relationships of the body of water treated, and so forth. The half-life of chemical residues in
water is not necessarily constant with time, but depends on the effects of various concentrations
of the herbicide on degradative organisms and other factors.
A number of chemicals that are persistent in soil are less persistent in water due to the action
of ultraviolet light. A herbicide that is resistant to degradation in soil, such as picloram, is more
easily decomposed by sunlight in surface water: it has a half-life ranging from 2 to 41 days, de-
pending on water depth, amount of sunlight, and water quality (Hedlund, 1970). More studies on
various herbicides concerning decomposition by sunlight are needed to help calculate a half-life
in water.
Residues in Air
Herbicide residues in air may be from three sources:
1. Spray and dust drift at the time of application (only 20 to 80 percent of the spray or
dust dispersed in air may reach the target) (Norris and Moore, 1970)
2. Dispersal of herbicides on particles due to wind erosion after application
3. Volatilization from treated areas (soil, water, plants, etc.) or other areas contaminated due
to the above three mechanisms.
Items 1 and 3 are most important.
Occasionally during periods of great winds, the accompanying dust storms may deposit herbi-
cides presumably carried over great distances (such as from Texas to Ohio) on contaminated or
treated particles (Cohen and Pinkerton, 1966). Even during normal weather, particulate matter
59
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suspended in air may adsorb volatile herbicides as it does DDT and lindane, and then be redeposited
on bodies of water or on the ground by rain storms some distance from the original source of
application (Abbott et al., 1965). Particles from air have been shown to contain 2,4,5-T in amounts
of 40 ppb (Cohen and Pinkerton, 1966).
To a lesser extent than drift, volatility may be responsible for considerable damage to sensitive
nontarget plants surrounding the target plants. The presence of herbicides in air in Washington
State has been studied with various salts and esters of 2,4-D (Adams et al., 1964). The role of
herbicide volatility is not well understood and is seen mostly when herbicide damage occurs to
valuable crops. The volatility of 2,4-D varies greatly depending on its form. For example, the
vapor pressure of the methyl ester is 100 or more times greater than that of 2,4-D (Hamaker and
Kerlinger, 1969). The volatility of a given herbicide from various treated surfaces varies greatly
depending on the weather, formulation, and adsorptive capacity of the surface from which the
herbicide volatilizes. Generally speaking, soil and other surfaces that adsorb herbicides to the
greatest extent allow the least volatility. Many soils lose a large percentage of an herbicide within
a few hours or days by volatilization.
Little is known of the fate of herbicides or other pesticides in air except that they are rapidly
diluted. The dilution factor is the main reason for difficulty in detecting herbicides in air since
present analytical methods are not sensitive enough to detect the low concentrations.
Sunlight alters the structure of many pesticides, especially in the presence of moisture and
particulate matter as occurs normally in air. Techniques for simulating these effects are not well
established. Compounds such as 2,4-D have been reduced to polymeric humic acids similar to soil
humic acids by both artificial light and sunlight (Crosby and Tutass, 1966).
ECOLOGICAL EFFECTS
Man controls his environment by employing different practices for managing his crops, roads,
parking lots, houses, utilities, and so forth. These practices are bound to have an ecological impact
on the environment. The purpose of this report is not to evaluate the success of these management
programs but rather to focus on an investigation of the unintentional ecological effects that may
result from employing herbicides as a tool in these management programs.
The desired effect of herbicides on target plants is to kill. However, this may not be accom-
plished totally, and the target plant may instead have an altered metabolism. This may also
happen to nontarget plants and microorganisms in the treated area. Obviously organisms differ in
their sensitivity to a toxic agent, and this sensitivity changes depending on the physiological state
of the organism. The resulting difficulty in precisely predicting effects probably explains the con-
tradictory claims regarding specific herbicide effects on various organisms (Pimentel, 1971).
Although herbicides are types of plant-growth regulators, their effect is not limited to plants.
Some animal species are quite susceptible to the direct action of herbicides (Table 1). The mammal
and bird species tested were relatively tolerant of herbicides, but in many cases fish were suscepti-
ble to dosages ranging from 0.010 ppm for trifluralin to 1000 ppm for chloramben.
A great range in susceptibilities is equally apparent among freshwater invertebrates (Sanders,
1970a and b). In tests of 16 herbicides against six species, dichlone was the most toxic. Species
differences also were evident; for example, the 48-hour LCSO of dichlone (fungicide) was 0.025
mg/1 for water fleas (Daphnia magna) and 3.2 mg/1 for crayfish.
Tadpoles of Bufo woodhousei tested at 4 to 5 weeks of age showed 96-hour LC50 values of
0.11 mg/1 for trifluralin, 1.2 mg/1 for endothall, and 14 mg/1 for paraquat (Sanders, 1967).
60
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Chronic effects of certain herbicides on fish have been reported (Eller, 1969). Endothall
(0.3 ppm) and potassium endothal (17.6 mg/1) produced ovalike cells in the testes of redear sunfish
and bluegills. The incidence of the cells was related to duration of exposure.
Herbicides may also affect nontarget organisms within a target area, such as the microorganisms
that are important in nitrification and degrading wastes. Audus (1970) concluded after a thorough
review that herbicide pollution, at least presently, does not constitute a serious threat to soil-
microbial equilibrium. He does note, however, rather large differences in response between different
microbial groups. Bacteria may either increase or decrease in number, depending on whether they
can utilize the herbicide as an organic substrate for growth. Nitrifying bacteria are, in general,
tolerant of most herbicides. However, nodule-forming rhizobia associated with legume plants and
cellulose-degrading microorganisms are sensitive, for example, to 2,4-D and fenuron, respectively
(neither chemical is recommended for use on legumes). Malone (1972) reported that repeated
applications of sodium cacodylate reduced species numbers and biomass in the community. He
also noted that litter decomposition was rapid in the sprayed areas, and this diminished an important
nutrient sink for the ecosystem. Sugar beets responded to a sublethal dosage of 2,4-D by increasing
the level of potassium nitrate from 0.22 to 4.50 percent (dry weight), which later proved highly
toxic when ingested by cattle (Stabler and Whitehead, 1950).
Herbicides may reduce or eliminate resistance in plants, rendering them more susceptible to
attack by pests. For example, red clover and oat strains resistant to pest nematodes lost their
resistance when exposed to low levels of 2,4-D (Webster and Lowe, 1966; Webster, 1967).
Exactly how 2,4-D eliminated the resistance response in these crop plants is unknown.
Herbicides may alter the nutritional content of crops—either increasing or decreasing their
food value. The protein content of oats, for instance, was increased with simazine (0.07 kg/ha)
by 28 percent over untreated oats (Schweizer and Ries, 1969). However, beans grown as a second
crop on previously treated soil were observed to have a lower level of protein than a control
(Anderson and Baker, 1950). Also, there was an increase in the carotene content of carrots treated
with linuron (Sweeny and Marsh, 1971).
Although little information is available, low levels of herbicides (2,4-D) seem to interact with
air pollutants such as SO2 and NHs to injure plants (Sherwood and Denisen, 1966); however,
herbicide interactions with other chemicals may reduce herbicidal activity.
In other situations, serious insect-pest outbreaks may follow the use of herbicides, thus requir-
ing the application of still more pesticide. Apparently, some weed killers alter the chemical makeup
of the crop plants, making them more attractive and nutritious to insects which consequently become
more abundant on the treated crop plants. Fox (1964), for example, reported that 2,4-D applied at
a rate of 1 and 2 Ib/acre increased wireworm damage to wheat (maximum dosage in the United
States is 0.5 Ib/acre). At a rate of 1 Ib/acre, 31 percent of the wheat plants were damaged, whereas
in the untreated check only 5 percent were affected. Putnam (1949) reported that the average
number of grasshoppers per square yard was about double in plots treated with 2,4-D (1 Ib/acre):
59 in plots treated with 2,4-D compared with 30 in the untreated control. The investigation did
not establish whether the increase observed in plots treated with 2,4-D was due to nutritional or
other changes in the plants.
Also, herbicides may indirectly stimulate the reproduction of pest insects. For instance, in bean
plants exposed to sublethal levels of 2,4-D aphid progeny production during a 10-day period was
increased from 139 to 764 per aphid (Maxwell and Harwood, 1960). Rice stalk borer larvae grew
almost 45 percent larger (35.1 mg versus 24.4 mg for the control larvae) during the 30-day experi-
mental period when rice plants on which the larvae fed were treated with 2,4-D (Ishii and Hirano,
1963).
61
-------
In addition, insect-pest outbreaks may be caused by herbicides because beneficial insect
predators are injured by the chemicals. Aphid outbreaks were reported on oats after the use of
2,4-D at a rate of 0.5 Ib/acre because fewer predaceous coccinellid beetles were present and active
in the crop (Adams and Drew, 1965). When applied at a rate of 0.5 Ib/acre, 2,4-D killed up to
75 percent of the coccinellid beetles and extended the normal developmental time from 16 to 27
days (Adams, 1960). Moreover, their normal predation activity was depressed, making these
beneficial coccinellid beetles less effective biological control agents (Adams and Drew, 1965).
Few quantitative studies have been made to ascertain the indirect effects of herbicides on the
population sizes of nontarget organisms in a system. However, because of animal and plant inter-
relationships, we would expect the population sizes of nontarget species to be either increased
or decreased after herbicide treatments. Moore (1967) indicates, for example, that the general
reduction in the sizes of bird populations in England may be attributed in part to the reduction of
shrubby roadside habitats by the use of herbicides. On the other hand, deer populations in
California were increased as a result of herbicide use. In the latter case, the subsequent resprouting
of killed shrub tops provided an increased food supply for deer (Krefting and Hansen, 1963).
Herbicides have been used with striking success to control gophers by selectively killing their food
source (Keith et al., 1959).
Moore (1967) described how herbicides may be used to control the population size of a
nontarget organism through rather indirect means. Partridge populations have declined in England
due in part to a decrease in insects that provide their major food supply during their early life
stages. The decline of the food supply is attributed to the reduction in the plant host of these
insects through the use of herbicides. Such a chain of events is diagrammatically indicated in
Figure 2. Partridge populations have declined in Germany apparently because herbicide use has
reduced their food supply and shelter.
Pond ecology and production also can be affected by herbicide use (Simpson and Pimentel,
1972). For example, simazine applied to 0.25-acre ponds at the rate of 1 or 3 mg/1 controlled
the weed Potamogeton foliosus and all filamentous forms of algae for almost 5 months (Mayer and
Mauck, 1971). It also lowered the pH of the water and drastically changed the species composition
of bottom-dwelling invertebrates. Residues persisted for at least a year.
Although the potential for harm exists, a number of herbicides can be used to control weeds in
aquatic sites without damage to fish and fish-food organisms (Walker, 1969a). For example, the
sodium salt of dalapon (2,2-dichloropropionic acid) was not hazardous to fish and other aquatic
animals at the recommended rate of 15 Ib/acre. Diquat, which is recommended for controlling
submerged weeds, algae, and floating aquatic plants, has a safe margin of toxicity to fish and fish-food
organisms. Residues are rapidly adsorbed on clay and disappear from the water. Endothall
(dipotassium and disodium salts) is recommended because it is relatively safe while controlling
most species of submerged aquatic plants. The methyl alkylamine salts are much more toxic to
fish. Trifluralin, in contrast, is one of the most toxic herbicides to fish, but under normal crop
use there appears to be little danger to aquatic habitats.
Unfortunately, little is known about the natural controls of weed species, aquatic or
terrestrial. Thus a given herbicide treatment may have unpredictable consequences. For example,
residual herbicides utilized to control fall-germinating cheat-grass result in the elimination of this
competitor to the spring-germinating sandbur, an equally undesirable weed. With the herbicide
leached by winter rain and competition reduced, the sandbur evidently flourishes (Roche, 1967).
62
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Weedy cereal crop
Diverse insect populations
(beetles, aphids, etc.)
Herbicide
Weed-free
crop
Large aphid
population
Cold
year
Adequate food for grey
partridge juveniles
Temperature-sensitive
aphids develop slowly
Partridge population
stable
Food inadequate for grey
partridge juveniles
Partridge population
declines
Figure 2. Interrelationships between herbicide usage and the size of gray partridge populations
in England (data from Potts, 1970)
63
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ECONOMIC AND ECOLOGICAL CONSEQUENCES OF
ALTERNATIVE WEED-CONTROL PRACTICES
Man controls weeds in crops, on industrial sites, and in aquatic systems as part of various
management programs. This chapter explains only the economic and ecological consequences of
weed-control practices employing herbicides or alternatives; it does not attempt to evaluate the
overall wisdom of these weed-control programs.
Crop Weed Control
Of all the herbicides applied in the United States, nearly 70 percent is used on crop lands,
and 85.2 percent of the land area treated with herbicides is crop land (USDA, 1971). Atrazine is
the most widely used herbicide, and corn receives more herbicides (over 40 percent) than any other
crop (Tables 3 and 4). Field crops, exclusive of pastures and rangeland, account for about 84
percent of all herbicides used in agriculture (USDA, 1970a). About 10 percent is used on pasture
and range and the remaining 6 percent on vegetables.
Although weeds reduce crop yields, they can be controlled by chemical means, by mechanical
cultivation, or by a combination of methods. Herbicide use on crops has increased because some
state and federal agencies have urged farmers to use herbicides and because chemical control in
some crops is more effective, economical, or convenient than mechanical cultivation.
Whether herbicidal or mechanical control is better depends on the particular crop, rotations,
soil, weather, weed species, and other conditions. As an example, consider the use of herbicides
versus mechanical cultivation in corn production. Corn is selected for this analysis because this
crop receives 41 percent of all the herbicides used in agriculture (USDA, 1970a). Weeds in corn
can be effectively and economically controlled by herbicides alone, by mechanical cultivation
alone, or by a combination of both methods. The factors that influence the choice of weed-control
method are discussed below.
Effectiveness.—Depending on weather, weed species, soils, and cropping systems, either
herbicidal control, mechanical control, or a combination may be more effective (Meggitt, 1960;
Drew and Van Arsdall, 1966; Armstrong et al., 1968; Buchholtze and Doersch, 1968). For example,
under wet conditions herbicides may be more effective than mechanical cultivation; under dry
conditions, however, mechanical control may be more effective. The trend toward using a combina-
tion of controls for weeds, according to Slife (1972), is the increased use of early-planted corn that
utilizes the full growing season, thus increasing yields. Planting in the Corn Belt about May 1 with
the long-growing varieties means that field conditions are wet and cool; hence there is a need for
herbicidal weed control in early spring.
Economics.—Depending on the weather, weeds, and labor availability, economic returns may
be highest in corn production employing herbicides, mechanical cultivation, or a combination for
weed control (Drew and Van Arsdall, 1966; Armstrong et al., 1968; Slife, 1972). The costs of
controlling weeds in corn with herbicides (two applications of herbicide) range from $10 to $14
per acre; costs for mechanical cultivations (three cultivations) range from $3 to $4 per acre. Often
a combination of herbicide and mechanical cultivation gives higher corn yields than either one
alone; sometimes ecdnomic returns are also higher (Drew and Van Arsdall, 1966; Armstrong et al.,
1968; Buchholtze and Doersch, 1968; Slife, 1972). For one companion crop of corn (soybeans),
four herbicide treatments cost $25 per acre for the growing season, whereas four cultivations cost
$12 per acre (Hauser et al., 1972). Hauser et al. also reported that mechanical cultivation resulted
in slightly higher soybean yields; however, Slife (1972) found that higher soybean yields were ob-
tained with a combination of herbicide and cultivation than with cultivation alone (control with
herbicide alone was not tested). For another companion crop (wheat), the use of one herbicide
treatment did not increase yields over those obtained without a herbicide (Slife, 1972).
64
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Table 4. ESTIMATED ACRES TREATED WITH SELECTED MAJOR HERBICIDES
IN THE UNITED STATES, 1966-19691'2
Type of use
Agricultural
Lawns and turf
Rights-of-way
U.S. Government
Private forests
Aquatics
Other
Total nonfarm
Total all uses
2,4-D
56,893
(39,513)
1,200
3,000
1,149
(2,225)
(4)
r>
<•.
(24,387)
(63,900)
2,4,5-T h A"
phenoxys
3451 62,454
(1655) (43,235)
1200 3,433
(600)
2175 (s)
(4368)
296 (4)
(656)
430 (5 )
(888)
81 199
(162)
306 1,521
(583)
4488 (4 )
(7257)
7939 (4)
(8912)
0. . Cacodylic A non-
Picloram
acid phenoxys
118 101 49,337
(81) (3) (69,185)
(3) (4) 1,371
c.
12 23 (4)
(16) (156)
(4) (6) 64
(3) (3) 17
(4) (4) 139
o r. <•>
c.
'Source: Anonymous.
2 Data given in thousands of acres. The numbers in parentheses are thousand pounds of active herbicide materials used.
3 Less than 500 acres treated.
4 Not available.
5 Included in other uses.
* Not registered for this use.
Insects and Diseases.—As already indicated, herbicide treatments may cause outbreaks of
insect and pathogen pests, which in turn may require insecticide treatment. Such outbreaks take
place because the crop plants lose their natural resistance to pests after herbicide treatment, be-
cause the plant becomes more nutritious for the pests, or because some natural enemies of the
pests are destroyed. Recent investigations have shown that aphids increase twofold on corn ex-
posed to 2,4-D (0.25 Ib/acre), and this same treated corn was significantly more susceptible to
corn smut disease (Oka and Pimentel, 1974). Oka (1974) has also found that European cornborer
larvae tend to grow larger on 2,4-D exposed corn than on untreated corn and that exposed corn is
significantly more susceptible to corn leaf blight.
Pollution.—Herbicides may pollute the surrounding environment by drift during application
and by either volatilization or runoff after application. The volatilization of 2,4-D, for instance,
may injure sensitive plants in the near vicinity of the treated area. The problem of herbicide runoff
depends on the slope of the land (White et al, 1967) and whether the herbicide has been worked
66
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into the soil. In addition to the dangers of direct runoff, silting is a problem. When herbicide treatments
are used, water runoff is greatest if no cultivation is used because the upper soil layer is relatively
smooth and closed. In contrast, with mechanical cultivation the upper soil layer is kept broken
and open, thereby facilitating the penetration of rainwater into the ground and the conservation
of soil.
In addition, pesticide pollution effects may be increased because herbicide use may create
new pest problems that require additional pesticides (see "Crop Rotations," below). Although
the difference is small, weed control with herbicides may require less energy (calories) than
mechanical cultivation. Based on the estimate that about 22 gallons of gasoline are used per acre
of corn (Pimentel et al, 1973) it was found that about 2 gallons are used per acre for three
cultivations (about 72,450 kilocalories per acre). The application of 2 pounds of preemergence
and 2 pounds per acre of postemergence herbicides requires about 80,225 kilocalories per acre
(11,000 kilocalories per pound of herbicide plus 1 gallon of gasoline for two applications).
Moisture and Land Conservation.—As mentioned, rain penetrates easily into mechanically
cultivated soil, thus conserving moisture. To determine whether plowing, no plowing (no tillage),
cultivation, or no cultivation is most effective in promoting moisture conservation is a complex
problem. Blevins et al. (1972) reported that with no-tillage culture of corn more moisture was
recorded in the upper 0- to 8-centimeter soil layer than with normal plowing. However, Drew and
Van Arsdall (1966) reported that with herbicide control the upper layer of soil was more compact
than with mechanical cultivation, and therefore there was greater moisture loss with herbicide
control because the capillary action was unbroken without cultivation. Hence the question of
moisture conservation remains unclear.
Herbicides, as mentioned, increase the yields of some crops and may release some land from
crop production. It has been estimated that if herbicides were not used and substitute practices
employed, losses due to weeds might increase from 8.5 to 10.2 percent (USDA, 1965; USD A,
1968; USDA, 1971; Pimentel, 1973). To make up this difference in crop production would require
as much as 2.3 million additional acres. Hence an estimated 2.3 million acres are probably released
from crop production and are available for other purposes.
Crop Rotations.—Weed control with herbicides may either reduce or prevent the rotation of
corn with crops of oats, soybeans, and other nonhosts of corn pests because of the hazards of
herbicide residues for these susceptible crops (Knake and Slife, 1962; Wisk and Cole, 1965; USDA,
1968; Swain, 1970; and Burnside et al., 1971). As a result, there may be an increased tendency to
grow corn on corn, and this may increase insect, disease, and weed problems. For example, a
pest problem that may occur from repeated corn croppings is the corn rootworm (Tate and Bare,
1946; Hill et al., 1948; Metcalf et al., 1962; Ortman and Fitzgerald, 1964; Robinson, 1966). The
resulting rootworm problem may require the use of additional pesticide (insecticide) for control.
This contributes to pollution and increases the overall costs of pest control.
Tradeoff of Herbicides and Price Supports.—The price-support and land-retirement program
encourages intensive agriculture. This may include using herbicides and other pesticides because
increasing yields have to be obtained on fewer and fewer acres. At the same time, crop-production
restrictions on previously productive lands may result in the culture of some corn on less fertile
land on a national basis, thereby increasing the production costs of the crop (Heady et al, 1972;
Pimentel and Shoemaker, 1974). Price supports and the land-retirement program cost the nation
nearly $5,000,000,000 during 1969 (USDA, 1970b). A careful analysis of the advantages of not
restricting the production of corn and other crops on some of the most fertile land of the nation is
needed. An analysis is also needed to determine the costs, benefits, and risks if mechanical
cultivation were substituted for herbicides in crop production. For example, based on the best
data available, it is estimated that it would cost $500,000,000 annually to substitute mechanical
control practices for control with herbicides in all crops (USDA, 1971; Pimentel, 1973).
67
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Conclusions.—Each particular crop situation and weed, insect, and disease control problem must
be evaluated based on solid economic and environmental analyses. Agricultural crop production can
more effectively meet the double challenge of increased production and decreased pollution by
adopting a systems approach to crop management. Based on this approach pest control becomes an
integral part of the total crop-management program. This type of pest control requires an under-
standing of the basic ecological mechanisms affecting the crop and the interactions of such diverse
factors as the pest, crop, water, soil, pesticides, fertilizers, rotations, sanitation, and other cultural
practices. Additional inputs in the analysis include economics, public health, and the environmental
impact of the system as a whole. With this approach, sound decisions about weed-control measures
are based on an analysis of the total costs and risks and the total benefits of all factors interacting in
the system.
Industrial Weed Control
Herbicides are used to control vegetation in many situations not directly associated with
agricultural crops. Major nonagricultural uses include the management of vegetation on roadsides,
rights-of-way, transmission lines, fire breaks, and parking areas. Of the total land area treated with
herbicides in the United States, 14.6 percent consists of rights-of-way and similar brush- and tree-
habitat areas (USDA, 1972). Rights-of-way alone amount to over 60 million acres (Niering, 1967).
Brush, trees, and other vegetation may interfere with transmission lines, block views, hinder passage
along roadways, or restrict other activities on rights-of-way. The largest industrial use of herbicides
is for brush control under transmission lines.
Brush and young trees can be effectively controlled by herbicides or by mechanical means
alone. When the concept of management is substituted for the concept of control, prescriptions can
be written to achieve the desired effect, and these prescriptions can include mechanical methods,
herbicides, or both. The factors that determine the choice of weed-control method are discussed
below.
Effectiveness.—In extremely rough terrain, where it is impossible to use tractors and other
heavy mechanical control equipment, herbicides are almost a necessity. On flat terrain, if only
grass cover is desired, mechanical means may be equally effective.
Economics.—Depending on the terrain and availability of labor in a region, weed control
is generally less expensive with herbicides than with mechanical means. Employing 2,4,5-T, brush
control on transmission-line rights-of-way costs about $6.50 per acre, whereas mechanical control
costs about $44 per acre (Office of Science and Technology, 1971). However, the costs of using
other herbicides run only slightly below those of mechanical control, or $42 per acre for brush con-
trol. Selective basal spraying is possible at essentially the same costs as blanket spraying. Along
road rights-of-way, herbicide control costs about $9 per mile per year, whereas mechanical control
costs about $16 per mile per year (McQuilkin and Strickenberg, 1962).
Animal Life.—In the management of rights-of-way, repeated blanket spraying produces and
maintains low ground cover. Selective basal spraying, however, produces a habitat of maximum
diversity, maintaining a variety of shrubs and herbs that produce fruit and seeds and attract a
varied animal life. Retreatments are needed much less frequently than with blanket spraying, and
costs are therefore essentially equal over a period of years (Svenson, 1966). This approach is no
longer a theory, it has had an adequate test by several commercial companies in the East (Hall and
Niering, 1959) and is widely used by some of them as standard practice (Potomac Electric Power
Co., 1964).
Pollution.—Herbicides may pollute environments adjacent to treated rights-of-way by drift dur-
ing application and by volatilization or runoff after application; the principal problem is drift. Be-
cause rights-of-way are normally a few hundred feet wide and extend for many miles through wild
habitats, the potential for polluting adjoining habitats is great.
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Runoff.—The elimination of some vegetation with herbicides may expose portions of the soil to
runoff and soil erosion. Since many grasses cover the bare areas quickly, this condition lasts only a
part of a season. With primarily a grass cover, the water yield measured in stream flow from the
treated watershed areas may be increased as much as 80 percent (USDA, 1970c). Although mechani-
cal control may result in reduced runoff in some cases, running tractors over the soil may leave
wheel tracks that collect water and eventually result in small washed gullies.
Conclusions.—Management practices for woody-plant control that bare the soil in rights-of-way
are detrimental in the long run. Through the judicious use of selective herbicides, total ecosystems
can be maintained.
Aquatic Weed Control
The management of aquatic plants by chemicals constitutes an ecological manipulation that is
more difficult to control and assess than the management of terrestrial plants. There are two princi-
pal reasons for this. First, natural waters constitute an active transport system; even the waters of
an apparently quiet pond are in motion due to changes in temperature, wind, evaporation, and in-
flow. A flowing stream carries chemicals far from the site of application in a very short time. In the
estuaries, the ebb and flow of tides facilitate the movement of chemicals. Second, the complex and
variable ecological systems of ponds, streams, and estuaries are at the base of a pyramid of aquatic
and terrestrial life whose ramifications cannot readily be traced. At present the kind of alterations
produced by herbicide use can be judged only in part.
Of the total area of the United States treated with herbicides, 0.2 percent is aquatic habitat
areas (USDA, 1972). Herbicides are used in aquatic habitats to control vegetation for better recrea-
tion, including fish and wildlife management (DeVaney, 1968; Walker, 1969b). Herbicides are also
used to control weeds in navigable channels and other waterways. Such treatments have resulted in
drastic reductions in the kinds and numbers of aquatic plants and animals, including fishes.
The most common herbicides used for the control of aquatic weeds are xylene, copper sulfate,
2,4-D, acrolein, endothall, and diuron (Anon., 1971).
Weeds in recreational waters and irrigation canals can be effectively controlled by herbicides,
mechanical means, and water-management practices. An analysis is made here of the advisability of
employing various weed-control techniques on recreational waters because this is a major use of
aquatic herbicides. Some of the factors influencing the desirability of employing one practice or a
combination of practices are discussed below.
Effectiveness.—For macroscopic plants either herbicides or mechanical means may be effectively
employed for aquatic weed control; however, microscopic plants like algae can be effectively con-
trolled only with herbicides. In some unique situations, aquatic weed problems might be effectively
controlled by management of the water system, which might involve diverting sewage, removing
nutrients, or changing water levels.
Economics.—Weed control under aquatic conditions is costly whether herbicides or mechanical
means are used. For example, the control of weeds in a recreational lake (Chautauqua Lake in New
York) cost an estimated $45 per acre ($37 for herbicide plus $8 for application) with herbicides and
$50 per acre (all costs, including hauling the weeds out of the lake) with mechanical means (Weaver,
1967). Although mechanical control was slightly more costly, it had the important advantage of
removing the weeds (including polluting nutrients) from the lake (see "Eutrophication," p. 74).
Feeding tests with cattle using dried, pelleted aquatic weeds have indicated that some aquatic weeds
were as good as alfalfa in both palatability and nutritive qualities (Vietmeyer, 1972). Hence, if weeds
can be used for animal feed, aquatic weed control by mechanical means could be more profitable
than control with herbicides.
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Fish.—For some weed problems, like the water-hyacinth, control may increase the fish popula-
tion for sport. However, in other situations, reducing aquatic weeds may result in reducing the popu-
lations of game fish such as bass and trout.
Pollution.—Acute and chronic toxic effects on certain species of fish and fish-food organisms
may occur after the use of herbicides. Another obvious secondary effect that results from the rapid
kill of aquatic vegetation is oxygen depletion. This is a more serious problem with herbicides than
with mechanical controls because herbicidal control can be carried out more rapidly and over
extensive areas. The long-term effects of habitat change on the aquatic system are not easily
appraised and because of this are generally unknown.
Eutrophication.—The most important reason for increased aquatic weed problems in recrea-
tional waters today is eutrophication, or the enrichment of lakes and rivers with nutrients,
primarily nitrogen and phosphorus. The sources of nitrogen are agriculture and urban and rural
sewage, whereas the source of phosphorus is primarily sewage. Aquatic weed problems could be
substantially reduced if the sources of nitrogen and phosphorus could be limited. Mechanical con-
trol has an important advantage over herbicidal control in that nitrogen and phosphorus are removed
in the weeds provided they are transferred completely from that ecosystem.
Conclusions.—Aquatic weed control is difficult, costly, and sometimes a problem environmen-
tally with either mechanical means or herbicides. The use of herbicides presents an additional
potentially dangerous factor. This can best be summarized by a statement from the National
Academy of Sciences 1968 report:
Although safe levels of more than 100 herbicides alone and in combination have
been tested for effects on fish production in aquariums for up to three years, factors
involved are so complex that data are inadequate to conclude whether a herbicide that
is nontoxic to fish will interfere with fish reproduction when applied at the lowest rate
needed to control weeds in a given body of water.
REFERENCES
Abbott, D. C., Harrison, R. B., Tatton, J. O., and Thomson, J., 1965. Nature, 208, 1317.
Adams, D. F., Jackson, C. M., and Bamesberger, W. L., 1964. Weeds, 12, 280.
Adams, J. B., 1960, Can. J. Zoo/., 38, 285.
Adams, J. B., and Drew, M. E., 1965. Can. J. Zool., 43, 789.
Akesson, N. B., November 1971, personal communication.
Akesson, N. B., Wilce, S. E., and Yates, W. E., 1971. "Atomization Control to Confine Sprays to
Treated Fields," Paper 71-662, Annual Meeting of the American Society of Agricultural
Engineers, December 7-10, 1971, Chicago.
Akesson, N. B., Yates, W. E., 1971. "Atomization Control to Confine Sprays to Treated Fields,"
Paper No. 71-662, Annual Meeting of the American Society of Agricultural Engineers,
December 7-10,1971, Chicago.
Akesson, N. B., Yates, W. E., and Christensen, P., 1972. "Aerial Dispersion of Pesticide Chemicals
of Known Emissions, Particle Size and Weather Conditions," paper presented at the 163rd
National Meeting of the American Chemical Society, Boston.
Anderson, G. R., and Baker, C. O., 1950. Agron. J., 42, 456.
Anderson, W. P., Richards, A. B., and Whitworth, J. W., 1969. Weed Sci., 16(2), 165.
Anonymous, 1970. Herbicide Handbook of the Weed Society of America, 2nd ed., W. F. Humphrey
Press, Inc., Geneva, N.Y.
Anonymous, 1971. Aquatic Herbicides (privileged source).
Applegate, V. C., Howell, J. H., Hall, A. E., Jr., and Smith, M. A., 1957. Toxicity of 4,346 Chemi-
cals to Larval Lampreys and Fishes, Special Scientific Report, Fisheries No. 207, U.S. Fish and
Wildlife Service, Washington, D.C.
70
-------
Armstrong, D. L., Leasure, J. K., and Corbin, M. R., 1968. Weed Sci., 16, 369.
Audus, L. J., 1970. Proc. 10th Weed Control Conf., p. 1036 (Weed Abstr., 20, 2389).
Axe, J. A., Mathers, A. C., and Wiese, A. F., 1969. Proc. Southern Weed Conf., 22, 367.
Battelle's Columbus Laboratory, 1971. Water Quality Criteria Book, Vol. 3, Effects of Chemicals on
Aquatic Life, U.S. Environmental Protection Agency, Washington, D. C.
Blevins, R. L., Thomas, G. W., and Phillips, R. E., 1972. Proc. No-Tillage Sys. Symp. February
21-22, Columbus, Ohio, pp. 140-145.
Brown, E., and Nishioka, Y. A., 1967. Pest. Monit. J., 1, 38.
Buchholtze, K. P., and Doersch, R. E., 1968. Weed Sci., 16, 232.
Burnside, O. C., Fenster, C. R., and Wicks, G. A., 1971. Weed Sci., 19, 290.
Butler, B. J., Akesson, N. B., and Yates, W. E., 1969. Trans. Amer. Soc. Agric. Engineers, 12(2),
186.
Butler, P. A., 1965. Proc. So. Weed Conf., 18, 576.
Cohen, J. M., and Pinkerton, C., 1966. In Advances in Chemistry Series, No. 60, American Chemical
Society, Washington, D. C., pp. 163-176.
Cope, O. B., McCraren, J. P., and Eller, L., 1969. Weed Sci., 17(2), 158.
Cope, O. B., Wood, E. M., and Allen, G. H. W., 1970. Trans. Amer. Fish. Soc., 99(1), 1.
Crosby, D. G., and Tutass, H. O., 1966. Agric. Food Chem., 14(6), 596.
DeGraff, H. F., and Washbon, W. E., 1943. Cornell Univ. Agric. Econ., 449.
DeVaney, T. E., 1968. Chemical Vegetation Control Manual for Fish and Wildlife Management
Programs, Bureau of Sport Fisheries and Wildlife Resource Publication 48.
Drew, J. S., and Van Arsdall, R. N., 1966. ///. Agric. Econ., 6, 25.
Duggan, R. E., Lipscomb, G. Q., Cox, E. L., Heathwole, R. E., and King, R. C., 1971. Pest. Monit.
J., 5(2), 73.
Eller, L. L., 1969. In Progress in Sport Fishery Research, Bureau of Sport Fisheries and Wildlife,
Resource Publication 77.
EPA, 1972. Data from the files of the Pesticide Regulation Division, U.S. Environmental Protection
Agency, Washington, D.C.
Fox, C. J. S., 1964. Can. J. Plant Sci., 44, 405.
Frank, P. A., 1971. "Herbicidal Residues in the Aquatic Environment," paper presented at the
161st National Meeting of the American Chemical Society, Los Angeles, March 1971 (reprint).
Frans, R. E., Davis, D. E., and Veber, J. B., 1972. Behavior of Specific Herbicides in Plants and
Soils, Southern Cooperative Series Bull. No. 167, Arkansas Agricultural Experimental Station,
University of Arkansas, Fayetteville.
Freed, V. H., 1966. In ASA Publication No. 8, Soil Science Society of America, Madison, Wis.,
pp. 25-43.
Getzendaner, M. E., 1960. A Residue Study ofSilvex in Fish Living in Kuron Containing Water,
Report GH-490, the Dow Chemical Co., Midland, Mich, (unpublished report).
Grzenda, A. R., Nicholson, H. P., and Cox, W. S., 1966. J. Amer. Water Works Assoc., 58(3), 326.
Hall, W. C., and Niering, W. A., 1959. In Proc. 13th Ann. Meeting N.E. Weed Control Conf.
Hamaker, J. W., and Kerlinger, H. O., 1969. In Advances in Chemistry Series, No. 86, American
Chemical Society, Washington, D.C.
Hansen, W. M., Quaife, M. L., Habermann, R. T., and Fitzhugh, O. G., 1971. Toxicol. Appl.
Pharmacol., 20, 122.
Hardy, J. L., 1966. In Down to Earth, 22(2), 11-13.
Hauser, E. W., Jellum, M. D., Dowler, C. C., and Marchant, W. H., 1972. Systems of Weed Control
for Soybeans in the Coastal Plain. Weed Sci., 20, 595-598.
Heady, E. O., Madsen, H. C., Nicol, K. J., and Hargrove, S. H., 1972. Future Water and Land Use:
Effects of Selected Public Agricultural and Irrigation Policies on Water Demand and Land Use.
Report of the Center for Agricultural and Rural Development, Iowa State University of Science
and Technology; prepared for the National Water Commission, PB-206-790 (NWC-EES-71-003)
NTIS, Springfield, Va.
Heath, R. G., Spann, J. W., Hill, E. F., and Kreitzer, J. F., 1972. Comparative Dietary Toxicities of
Pesticides to Birds. Special Scientific Report, Wildlife No. 152, Patuxent Wildlife Research
Center, Bureau of Sport Fisheries and Wildlife, Laurel, Md.
71
-------
Hedlund, R. T., 1970. The Rate of Photodegradation of Picloram in Aqueous Systems, Report
GS-1089, the Dow Chem. Co., Walnut Creek, Calif, (unpublished report).
Hill, R. E., Hixon, E., and Muma, M. H., 1948. J. Econ. Entomol., 41, 392.
Hoerger, F., and Kenaga, E. E., 1972. Environ. Quality and Safety, 1, 9.
Ishii, S., and Hirano, C., 1963. Entomol. Exp. Appl., 6, 257.
Johnson, R. E., Carver, T. C., and Dustman, E. H., 1967. Pest. Monit. J., 1, 7.
Kearney, P. C., 1966. In Advances in Chemistry Series, No. 60, American Chemical Society,
Washington, D.C., pp. 250-263.
Keith, J. O., Hansen, R. M., and Ward, A. L., 1959. J. Wildl. Manag., 23, 137.
Kenaga, E. E., 1968. Down to Earth, 23(4), 11,16.
Kenaga, E. E., 1972. Residue Rev., 44, 73-113.
Knake, E. L., and Slife, F. W., 1962. Control Those Weeds Early, Illinois Agricultural Experimental
Station Circular 843.
Krefting, L. W., and Hansen, H. L., 1963. Southern Weed Conf., Proc., 16, 209.
Lawrence, J. M., 1962. Aquatic Herbicide Data, Agricultural Handbook No. 231, U.S. Department
of Agriculture, Washington, D.C.
Lawrence, J. M., 1963. Aquatic Herbicide Data, Supplement 1, Agricultural Experimental Station,
Auburn University, Auburn, Ala.
Malone, C. R., 1972. Ecology, 53, 507.
Martin, H., 1968. Pesticide Manual, 1st ed., British Crop Protection Council, London.
Mayer, F. I., Jr., and Mauck, W. L., 1971. In Ann. Progress Report: 1971, Fish-Pesticide Research
Laboratory, Bureau of Sport Fisheries and Wildlife, Columbia, Mo.
Maxwell, R.C., and Harwood, R. F., 1960. Ann. Entomol. Soc. Amer., 53, 199.
McCraren, J. P., Cope, O. B., and Eller, L., 1969. Weed Sci., 17(4,), 497.
McKee, J. E., and Wolf, H. W., 1971. Water Quality Criteria, 2nd ed., Publication 3-A, the Resources
Agency of California, State Water Resources Control Board.
McQuilkin, W. E., and Strickenberg, L. R., 1962. Conn. Arboretum Bull, No. 13, p. 3.
Meggitt, W. F., 1960. Proc. N.E. Weed Control Conf., 14, 240.
Metcalf, R. L., Flint, W. P., and Metcalf, C. L., 1962. Destructive and Useful Insects, McGraw-Hill,
New York.
Miller, R. W., 1972. "Adsorption of Phenols and Phenoxyacetic Acids by Organoclays in Water,"
paper presented at the American Chemical Society Northwest Section Meeting, Corvallis, Oreg.,
June 1972 (abstract).
Moore, N. W., 1967. Proc. Roy. Soc. (London), B167, 128.
National Academy of Sciences, 1968. In Quarterly Progress Report, April-June 1967, Fish-Pesticide
Research Laboratory, Bureau of Sport Fisheries and Wildlife, Columbia, Mo., p. 357.
Newton, M., and Norris, L. A., 1968. In Proc. 22nd West Soc. Weed Sci., p. 32 (abstract).
Niering, W. A., 1967. Conn. Woodlands, 32(1), 6.
Norris, L. A., 1971. J. Forestry, 69, 715.
Norris, L. A., and Moore, D., 1970. In Symposium: Forest Land Uses and Stream Environment,
Forestry Extension, Oregon State University, Corvallis, Oreg., pp. 138-158.
Oka, I. N., 1974. Personal communication.
Oka, I. N., and Pimentel, D., 1974. Environ. Entomol. (in press).
Office of Science and Technology, 1971. Report on 2,4,5-T. A Report of the Panel on Herbicides of
the President's Science Advisory Committee, U.S. Government Printing Office, Washington,
D.C.
Ortman, E, E., and Fitzgerald, P. J., 1964. Proc. Ann. Hybrid Corn Industry Res. Conf., 19, 38.
Palmer, J. S., 1972. Toxicity of 45 Organic Herbicides to Cattle, Sheep, and Chickens, Production
Research Report No. 137, Agricultural Research Service, U.S. Department of Agriculture,
Washington, D.C.
Palmer, J. S., and Radeleff, R. D., 1969. The Toxicity of Some Organic Herbicides to Cattle, Sheep,
and Chickens, Production Research Report No. 106, Agricultural Research Service, U.S.
Department of Agriculture, Washington, D.C.
Pimentel, D., 1971. Ecological Effects of Pesticides on Non-target Species, Executive Office of the
President, Office of Science and Technology, Washington, D.C.
72
-------
Pimentel, D., 1973. J. N.Y. Entomol. Soc., 81, 13-33.
Pimentel, D., and Shoemaker, C. A., 1974. Environ, Entomol., 3, 10-20.
Pimentel, D., Hurd, L. E., Bellotti, A. C., Forster, M. J., Oka, I. N., Sholes, O. D., and Whitman, R.
J., 1973. Science, 182, 443-449.
Potomac Electric Power Co., 1964. Specifications for Basal Method of Spraying Woody Plants on
PEP Co. Transmission Rights-of-Way on a Lump Sum Basis.
Potts, G. R., 1970. Proc. 10th Br. Weed Control Conf., 1, 299.
PSAC, 1965. Restoring the Quality of Our Environment, Report of the Environmental Pollution
Panel, President's Science Advisory Committee, Washington, B.C.
Putnam, L. G., 1949. Sci. Agric., 29, 396.
Reimer, C. A., Byrd, B. C., and Davidson, J. H., 1966. Down to Earth, 22(1), 3.
Reid, C. P., and Hurtt, W., 1970. Physiol. Plant., 23(1), 124.
Robinson, R. E., 1966. Agron. J., 58, 475.
Roche, B. F., 1967. In Symposium Proceedings. Herbicides and Vegetation Management in Forest,
Ranges, and Non-crop Lands, School of Forestry, Oregon State University, Corvallis, Oreg., pp.
259-264.
Rosen, J. D., 1972. Environ. Quality and Safety, 1, 85.
Sanders, H. O., 1967. In Quarterly Progress Report, April-June 1967, Fish-Pesticide Research
Laboratory, Bureau of Sport Fisheries and Wildlife, Columbia, Mo., p. 5.
Sanders, H. O., 1970a. J. Water Pollution Control Fed., 42(8), 1544.
Sanders, H. O., 1970b. In Progress in Sport Fishery Research 1969, Bureau of Sport Fisheries and
Wildlife, Resource Publication 88, pp. 7-8.
Schweizer, C. J., and Ries, S. K., 1969. Science, 165, 73.
Scifres, C. J., Hahn, R. R., Diaz-Colon, J., and Merkle, M. G., 1971. Weed Sci., 19(4), 381.
Sheets, T. J., and Harris, C. L, 1965. Residue Rev., 11, 123.
Sherwood, C. H., and Denisen, E. L., 1966. Abstracts Weed Soc. Amer., p. 68.
Shimabukuro, R. H., and Swanson, H. R., 1969. J. Agric. Food Chem., 17, 199.
Simpson, R. L., and Pimentel, D., 1972. Search, Cornell University Research Publication 2(10),
1-59.
Slife, F. W., 1972. Personal communication.
Smith, G. E., and Isom, B. G., 1967. Pest. Monit. J., 1(3), 16.
Stahler, L. M., and Whitehead, E. I., 1950. Science, 112, 749.
Svenson, H. A., 1966. Vegetation Management of Rights-of-Way. Selective Maintenance for
Improved Wildlife Habitats and Scenic Values, U.S. Forest Service, Eastern Region.
Swain, D. J., 1970. Agric. Gaz. New S. Wales, 81, 400.
Sweeney, J. P., and Marsh, A. C., 1971. J. Agric. Food Chem., 19, 854.
Tarrant, R. F., and Norris, L. A., 1967. In Proc. Symp. Herb, in Veget. Management (Oregon State
University), p. 81.
Tate, H. D., and Bare, O. S., 1946. Corn Rootworms, Nebraska Agricultural Experimental Station
Bulletin No. 381.
USDA, 1965. Losses in Agriculture. Agricultural Handbook No. 291, Agricultural Research Service,
U.S. Department of Agriculture, Washington, D.C.
USDA, 1968. Extent and Cost of Weed Control with Herbicides and an Evaluation of Important
Weeds, 1965, Agricultural Economic Report No. ARS 34-102, Economic Research Service,
U.S. Department of Agriculture, Washington, D.C.
USDA, 1970a. Quantities of Pesticides Used by Farmers in 1966, Agricultural Economic Report
No. 179, Economic Research Service, U.S. Department of Agriculture, Washington, D.C.
USDA, 1970b. Agricultural Statistics 1970, USDA. Department of Agriculture, Washington, D.C.
USDA, 1970c. Forestry Research Highlights, Rocky Mountain Forest and Range Experimental
Station.
USDA, 1971. Restricting the Use of Phenoxy Herbicides, Agricultural Economic Report No. 194,
Economic Research Service, U.S. Department of Agriculture, Washington, D.C.
USDA, 1972. Extent and Cost of Weed Control with Herbicides and an Evaluation of Important
Weeds, 1968, Agricultural Research Service and Economic Research Service, U.S. Department
of Agriculture, Washington, D.C.
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USDA, 19Z3. The Pesticide Review, 1972, Agricultural Stabilization and Conservation, U.S.
Department of Agriculture, Washington, D.C.
Van Middelem, C. H., 1966. In Advances in Chemistry Series, No. 60, American Chemical Society,
Washington, D.C., pp. 228-249.
Van Valin, C. C., 1966. In Advances in Chemistry Series, No. 60, American Chemical Society,
Washington, D.C., pp. 271-279.
Vietmeyer, N. D., 1972. Processed Aquatic Weeds Show Promise as a Source of Cattle Feed,
Infoletter No. 8, International Plant Protection Center, Oregon State University, Corvallis, Oreg.
Walker, C. R., 1969a. In Fish and Chemicals. A Symposium on Registration and Clearance of
Chemicals for Fish Culture and Fishery Management. New Orleans, La., September 12, 1969.
Walker, C. R., 1969b. In Progress in Sport Fishery Research 1968, Bureau of Sport Fisheries and
Wildlife, Resource Publication 77, pp. 90-91.
Weaver, W. G., 1967. "Aquatic Weed Control," news release by Chautauqua Lake Association,
February 26, 1967.
Webster, J. M., 1967. Plant. Pathol.} 16, 23.
Webster, J. M., and Lowe, D., 1966. Parasitology, 56, 313.
Wershaw, R. L., Burcar, P. J., and Goldberg, M. C., 1969. Environ. Sci. Technol., 3(3), 271.
Wisk, E. L., and Cole, R. H., 1965. Proc. N.E. Weed Control Conf., 19, 356.
White, A. W., Barnett, A. P., Wright, B. G., and Holladay, J. H., 1967. Environ. Sci. Technol., 1,
740.
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AGRICULTURAL AND OTHER APPLIED USES
FINDINGS
Forest Management
1. Herbicides are one of many management tools available for improving yields from commer-
cial forest lands. The economic consequences of no management of forest lands are severe. Original
cutting may leave undesirable species which remain dominant thereafter. The use of least disturbing
practices tends to promote forest stability with minimum loss due to erosion and nutrient leakage.
2. Herbicides are the most selective method (other than hand labor) of eliminating shrub or
cull-tree species to enhance desirable forest growth. The beneficial effects of properly applied
herbicides outweigh the risks. The benefits from herbicide use span many years, whereas the risks
are short-lived because herbicide residues dissipate in a period of months, or less. The effects on
habitat, desirable or undesirable, depend on the original habitat condition.
3. Herbicides can be applied with minimum damage to our natural resources when used prop-
erly. In forestry, herbicides are generally applied by aircraft. By careful application, the subsequent
movement of herbicides can be controlled. Drift can seriously damage susceptible nontarget orga-
nisms. There is evidence that fish and food-chain organisms have not been seriously affected by the
level of phenoxy herbicides contaminating streams. Occupational and personal health risks are mini-
mal.
Grazing Lands
1. It is impossible to control weeds on grazing lands without some ecological impact. The pur-
pose and primary impact of weed and brush control is to change the vegetative composition of the
grazing site from brush and weed to "grassland," which may be a subclimax vegetational type. Since
residues are relatively short-lived in soils and dissipate rapidly from animal tissues, they are not con-
centrated in the food chain.
2. Aerial spraying is the only practical means of herbicide application on the more extensive
brush-infested ranges and pastures. While mechanical methods are used where applicable, they are
usually expensive, relatively nonselective, often less effective, and often must be accompanied by
reseeding.
3. Because of herbicides' selectivity, the nontarget species of plants that are not killed increase
in size and cover coincident with the slow death of unwanted species and thus continuously provide
more cover for wildlife species, and more protection against soil erosion than other methods of control.
Aquatic Uses of Herbicides
1. In all but a few instances, the efficacy of herbicides has exceeded that of presently available
alternatives for aquatic plant control. Mechanical methods will continue to be employed where appli-
cable or in sensitive areas. A few species may be controlled with biological control agents but there
will have to be continued heavy reliance on chemical techniques as a part of the total technology for
controlling aquatic and ditchbank weeds.
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2. Intentional modification of aquatic habitats affects wildlife in various ways. Complex eco-
logical systems may undergo far-reaching changes not yet fully elucidated by research. Food plants
and nesting sites may be degraded. Conversely, thinning or modification of aquatic weeds may im-
prove such sites and reduce potential oxygen depletion when overabundant plants die and decay.
Herbicides in Crops
1. Worldwide losses from weeds, due to reduced crop yield and quality, together with the cost
of weed control, amount to 10 to 15 percent of the total value of agricultural and forest products.
During the last 20 years, the use of 2,4-D to control weeds on an accumulated total of 460 million
acres of wheat increased the yield by about 2 billion bushels—enough wheat to supply each American
family with over 6 years' supply of bread. Chemical weeding permits simplification of crop rotation,
avoidance of soil disturbance, adjustment of row spacing to the optimum for each crop, mechaniza-
tion, and economy of labor.
2. There is no evidence that agricultural uses of herbicides cause an accumulation of residues in
humans, domestic animals, or wildlife. Evidence from monitoring studies indicates there is little over-
all buildup of residues in soils; persistence is relatively short. Major herbicide problems have been
drift to nontarget species, some instances of persistence in soil, and contamination of waters.
3. In crop production, the use of herbicides, along with other weed-control methods, has not
only reduced labor input and cost of production, but has increased yields. For example, in the past
decade the amount of hoe labor for cotton production in certain areas of the United States was re-
duced from 48 to 13 man-hours per acre by the use of herbicides. The cost of labor for weeding
strawberries decreased from as much as $200 to as little as $16 per acre where selective herbicides
were used in combination with tillage. A significant portion of the 900-lb.-per-acre increase in rice
yields in the United States from 1961 to 1969 resulted from improved weed control through the in-
creased use of herbicides. This increase in yields represented a dollar value of approximately
$90,000,000 for 1969 alone.
4. The ability to control weeds is as important to the individual grower of minor acreage crops
(e.g., asparagus and berries) as to the grower of major acreage crops (e.g., corn and cotton). With the
current increase in total registration requirements, few herbicides will be developed for the producer
of minor crops. The manufacturer's economic return from the sale of a herbicide for a minor crop
use does not warrant the cost of development of registration information. A procedure must be de-
veloped whereby growers of minor crops may be assured of the continued development of improved
herbicides for their needs.
The term "minor crops" has been misleading. A newer term—"minor uses"—more clearly de-
fines the problem. Now that registrations must be for specific weed-crop situations, a particular use
where the volume of herbicide does not justify the cost of registration should be considered a minor
use.
5. In fruit and nut crops, the cost of hand labor has become almost prohibitive on a commer-
cial basis. In certain orchards mowing is effective. Increased growth and yields result from herbicide
use in conjunction with mechanical weed-control techniques.
Industrial Weed Control
1. On some industrial sites where weed control is required, nonchemical weed control methods
may be used effectively. On other industrial sites, herbicides are the only practical method. The need
for visibility, accessibility, moisture conservation, fire-hazard control, and the prevention of vegetation
fouling are some of the factors which may require weed and brush control. Hand-labor costs and
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steep terrain may prevent the use of nonchemical methods. Some drift and leaching potential, ero-
sion, and reduction of animal cover may result from certain applications of herbicides.
FORESTS
The Forest as a Resource
Approximately 500 million acres of the continental United States are commercial forest land.
The timber growing on this land constitutes the major renewable source of raw material for fiber
and shelter. The annual production of some 50 billion board feet of timber from these lands has a
direct annual value of over $5,000,000,000 and a substantially greater value when considering the
secondary industries this supplies.
It is evident in considering our forest-resource statistics, together with the histories of Euro-
pean nations supporting commercial forests, that the forests of the United States can continue in-
definitely to produce raw materials at the existing rate. Capacity exists for substantially increased
production, but the present condition of these forest lands with respect to weeds imposes an upper
limit on the amount that can be cut without a further deterioration in quality (USDA, 1965; New-
ton, 1973a).
Forests are important areas for the management of wildlife, water supplies, and various other
nonsalable byproducts. Nontimber values, especially those related to recreation, are increasing at a
rapid rate. Qualities that make a forest attractive for lumbering (i.e., high quality, large trees, and
good access) also make it attractive for recreation. The forest owner or manager in meeting his so-
cial responsibilities must maintain the nontimber values while relying solely on timber for operating
revenue. His ability to maintain all values depends on his success in replacing trees currently being
harvested and keeping these stands in good condition.
The forests of the United States are in various conditions. The hardwood and coniferous for-
ests of the East have been heavily cut over, with regrowth mostly of inferior species and forms
(USDA, 1965); the coniferous forests of the West are generally in better condition. Unfortunately,
the inventories of American forests do not reflect directly the potential for improvement in produc-
tivity. Comparisons of average forests with those under ideal management always provide an overly
optimistic estimate of the values that can be achieved by management. Actually we should be receiv-
ing a much greater yield from most of the commercial forest lands in this country. It was estimated
that 26 percent of the commercial forest land, or 114 million acres, was poorly stocked or not stocked
at all with commercial species in the 48 states inventoried in 1953. At that time resource inventories
indicated that a "reasonable" level of management would double the growth of timber to 100 billion
board feet per year (USDA, 1958). Walker (1973) indicated that 300,000,000 acres of commercial
forest land are producing at less than 70 percent of their potential in native species, with losses at-
tributable to weeds only. Most of this potential can be achieved by the restoration and maintenance
of original species composition on cutover lands. The same practices would also improve the status
of the nontimber resources in both the long and short run.
Many management tools are available to forest managers for achieving yields of whatever com-
modities are desired from commercial forest lands. Nearly all involve replacing undesirable vegeta-
tion with desired tree species. Herbicides are just one of many tools that can be used to suppress the
undesirable species. Herbicide use must be evaluated, however, in comparison with the comparable
features of alternative methods. Such a comparison is the purpose of this guide. As a technical sup-
plement, the March 1973 issue of the Journal of Forestry was devoted almost entirely to this sub-
ject.
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Unique Features of Forests Under Management
The major differences between annual croplands and forests are the result of the difference in
time during which the crop accumulates. Forests, in general, retain large amounts of naturally oc-
curring soil nutrients in the living vegetation and litter. They also sustain a highly complex system
of secondary organisms that depend on forest production for their sustenance. Soil-profile develop-
ment, with its substantial layer of litter and humus, provides a tree-dependent soil-fungi complex
that is unique. Similarly, such soil development maintains a substantial community of insects and
worms that is largely confined to forests although not unique to them. Wildlife habitat provided by
forests is unique in the sense of providing cover along with a supply of undergrowth for forage.
Unique as forests are from the standpoint of biological structure, many of our croplands were
once forests and differ only in having been deforested. Many of the cleared lands abandoned in past
economic crises have been reinvaded by forests with no appreciable loss of productive potential.
Thus the outstanding characteristic of a forest is the dimension of a time sequence in which various
life systems can develop. Such time dependency in forest-resource management places stringent
economic constraints on operating alternatives.
The primary producers of a forest, principally the dominant trees, control the local forest en-
vironments. The length of time needed to grow trees to 75 percent of their mature size ranges from
30 to over 150 years. Investments in forest management therefore carry a very large interest accu-
mulation. Thus forest environmental management investments must be made far in advance of har-
vest, with costs kept to an absolute minimum.
The public has a major stake in the resource dominated by such trees. The landowner is asked
by the public to maintain the resource. Yet the public is also involved in an economic system that
taxes a salable tree every year and offers alternative investments that encourage timber owners to
cut all salable trees and invest the income elsewhere. Under the circumstances, the public has a
clear responsibility to support the development and implementation of forestry practices that pre-
serve resource values economically but will not cause more harmful effects than the practices they
replace.
The Forest as a Dynamic System
The time dependence of forest life-support systems bears careful analysis. Trees must grow in
order to live. Most of the commercial timber species need to be the largest individuals in a forest to
avoid being shaded out of the stand. As juveniles they may be crowded out by more successful
plants that may or may not have some value in management. The forest manager, regardless of man-
agement objectives, must ensure that desirable species have access to sufficient resources to continue
growing indefinitely. Whether a plant is removed by herbicides, by wildlife browsing, or by harvest-
ing another plant will replace it (Newton, 1973a). In general, the more violently one disturbs a forest,
the more rapidly the forest structure changes after the disturbance. After clearcutting or scarification
with a bulldozer (analogous to ploughing a field), weeds, shrubs, and noncommercial trees grow in
profusion together with seedlings of commercial species. Resources are usually fully utilized by plants
within a very short time after such disturbance, and individuals of many species sustain heavy mor-
tality through crowding. When commercial species are jeopardized by other plants, the forester em-
ploys various management tools to ensure that growth resources continue to be available for the
species he wishes to grow (Gratkowski, 1967).
Not all of the forester's tools involve such drastic disturbances as clearcutting or scarification.
Selective felling, single-tree poisoning, and selective spraying are all far less destructive than com-
plete scarification in preparation for planting. Because they make fewer changes in stand structure,
organisms dependent on forest structure are displaced less. Moreover, the use of the less disturbing
practices tends to promote stability of forest composition with a minimum of losses due to erosion
and nutrient leakage. The theory of forest dynamics under manipulation has been outlined by
Newton (1971, 1973b).
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History of Forest Exploitation
Most of the commercial forests of the United States have undergone a history of exploitation,
some for as long as 250 years. The hardwood forests of the East, especially, have been subjected to
chronic removal of the most desirable trees. The trees remaining, after the best trees have been har-
vested, make up increasingly defective forests. Many areas of the Eastern United States support
forests that are growing perhaps one-half or two-thirds as much total wood as their productive
capacities would suggest. In addition, the value of the wood and the condition of the wildlife habi-
tat are very severely impoverished by poor species composition (Benzie et al., 1973; Fitzgerald et
a/,, 1973). Thus, although forest-inventory statistics imply that forests are growing more wood than
is being harvested, these figures do not indicate that the quality of wood is being maintained or even
that the products that are growing are more than marginally utilizable (USDA, 1965).
The condition of the forest is worst in the most poverty-stricken areas of the United States.
Over 100 million acres in Appalachian and southern hardwood regions are capable of supporting
very high quality raw material in forests, yet they are producing at a small fraction of their potential
(USDA, 1965). High-quality raw materials are desperately needed for economic stability. Incentives
for forest improvement both for industrial raw material and for wildlife habitat are needed badly.
Because such vast areas are involved and because the economic consequences of no action are so
severe, appropriate tools must be available to land managers for forest improvement. The degree to
which the tools are appropriate must be given careful scrutiny.
Operating Premises and Management Alternatives
Every forest-management operation has both ecological and economic implications. The issues
involved in regulating forest practices are viewed very differently by the voting majorities, on the
one hand, and by private forest owners and public land managers on the other. Several operating
premises that related to the fundamental decision processes involving herbicides can be outlined.
Since these are based on certain value judgments, they are arguable. They do, however, make possi-
ble some comparisons of alternatives on the tactical, rather than the strategic, level; it is at this level
that the decision between herbicide and nonherbicide methods may be made rationally.
Premise I: Once-productive forests that for various reasons have little prospect of restoration
to desirable composition and form without man's intervention justify such intervention.
This premise assumes the following:
1. The environmental impact of mismanagement still persists on such lands, and restoration
toward original species composition is a means of removing an existing undesirable, manmade condi-
tion.
2. Forest rehabilitation is needed only once in any given stand since desirable composition can
be maintained by continued appropriate management.
3. A base for forest production is needed indefinitely.
4. Forest resources of all kinds can be maintained with the least adverse effects if the broadest
possible resource base is under management.
5. Steps taken to improve the resource base must be planned in advance of product need,
ranging from a few years in the case of wildlife to 80 years or more for optimum timber or recrea-
tion use.
The issue of whether wild land should be placed under management is not involved here, since
the effects of poor management are already prevalent in forests justifying treatment. Thus, the
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choice is whether management is to revert to and maintain original composition or to permit contin-
uation in shrub or cull-tree cover abnormal to the site. Once the management objective has been
decided on, an approach toward implementation can be outlined. The question of herbicides can
then be considered in relation to alternative methods directed toward the same objective.
Approaches to Forest Rehabilitation.—The goal of forest rehabilitation is to grow desirable
species. Two general approaches are common, depending on the initial presence or absence of desir-
able trees. Where stands contain enough desirable trees, but undesirable trees prevent them from
becoming dominant, they do not need planting. Site resources, being preempted by undesirable
plants, can be made available to the desirable trees by removing undesirables, and desirable vegeta-
tion can then become dominant. This condition is common in eastern hardwood forests. In the other
situation, very common in coniferous forests, sites occupied by undesirable vegetation to the exclu-
sion of desirable trees require provision for establishment and maintenance of the trees as well as
vegetation removal. The newly established trees must be provided adequate site resources continu-
ously for several years to prevent excessive mortality. In both cases rehabilitation involves the pro-
vision for adequate numbers qf desirable trees to occupy a site and for allocation of site resources in
their support.
In all forest ecosystems the dominant vegetation controls the availability of site resources
(Newton, 1973). Both of the above approaches involve treatment of vegetation to redistribute
resources between desirable and undesirable forms. Stands with desirable trees already established
do not normally require treatments having prolonged direct effects; establishment of trees from
seedlings requires longer periods of control.
The methods of releasing resources for tree growth all involve removal of associated plants.
The elimination of certain plants influences resource supplies for trees; it also affects food supplies
for insects, birds, and mammals. How the plants are killed affects the quality and quantity of re-
growth and the physical environment in which it is growing. The degree of physical disturbance also
determines the extent of physical injury to wildlife and habitats, as well as exposure of soil to
weathering and erosion.
Vegetation-control practices entail either physical violence or toxic action. Most forest-
rehabilitation operations involve some of each. Given a land area in need of treatment, the choice of
methods includes only those with some objectionable features. The decision of whether to treat is
likely to be based on costs of undesirable side effects balanced against returns and desirable side
effects. The choice of method involves costs, expectation of success, and impact on resource values
in addition to timber. The following discussion of methods includes various chemical and non-
chemical techniques. Because this is a guide for chemically oriented decisions, emphasis is on chemi-
cal methods; nonchemical tactics are considered as counterparts only sufficiently to identify their
role as alternatives to chemicals. Both groups of methods are discussed according to their economic
and ecological impacts when applied with adequate provisions for achieving comparable objectives.
Before considering methods in detail, nontimber values of forests must be considered in rela-
tion to timber management. Timber is the primary revenue-producing forest product. Management
for optimum timber production, however, has multiple effects on wildlife, water quality and yield,
and aesthetics. These effects are likely to be interpreted differently in long- versus short-term evalu-
ation. In many instances, enhancement of one value is offset by a decrease in another. For example,
management of primary forest tree species in long rotations to enhance recreation opportunity has
the positive effect of providing large trees, eagle perches, and attractive scenery and the negative
effects of poor forage for big game and low return on investment (Black, 1974). Details of value
changes and tradeoffs are discussed under premise II. The following discussion covers ecological
effects of both groups of methods. Specific chemicals and their properties are reviewed under prem-
ise III, relating to environmental hazards and management alternatives.
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Forest Practices Toward Rehabilitation.—Rehabilitation involves the establishment of trees and
practices that guarantee their continued survival. The following discussion of practices assumes that
provision has already been made for stocking of trees and that cultural treatment is in support of
plantation survival. It also assumes that ecological analysis has identified vegetation and vegetation-
dependent factors as being the primary obstacles to stand development.
Chemical Con trol. —Herbicides are one of several groups of important tools in vegetation man-
agement. Of the various plant-killing methods, they are the most selective, they alone have biologi-
cal effects persisting after treatment, and they exert their effects without violence. They achieve
their effects exclusively through toxic action on sensitive plants. This is done with more or less no
effect on resistant species, depending on the degree of resistance, and negligible toxic or physical
injury to mammals under operational conditions, as far as is known (Norris, 1971).
Chemical practices have been developed to divert to trees resources tied up by several groups
of competitors. They have also been used to eliminate various nonvegetative pests that are present
in response to certain ecological conditions (Lawrence, 1967; Laird and Newton, 1973; Newton and
Holt, 1971). These practices accomplish their objectives through the natural tendency of plants to
utilize available resources; suppressing various plant groups leaves resistant plants more free to grow.
Suppression of all vegetation, without the provision for species capable of using the released re-
sources, may cause loss of such resources, especially nutrients (Likens et al., 1970); such practices
are not recommended in constructive forest management.
Chemicals used to control forest vegetation generally have a short life. Their direct effects are
almost exclusively confined to plants in the sense that known toxic levels to mammals and other
wildlife are much higher than those encountered in their use operationally (Warren, 1967). Their
direct effects on plants cause an important restructuring of species abundance among plants.
The effect on animal habitats is great (Lawrence, 1967). Whether this is beneficial or detri-
mental depends on the condition of the habitat initially and the desirability of gains or losses among
various animal species. The restructuring of dominance in the plant community is deliberately
aimed at encouraging desired species, generally with the objective of permanent change. Thus the
life of the effect of the herbicide is much greater than the life of the chemical in the environment.
All organisms dependent on primary producers are affected by change in cover, regardless of
whether chemicals have been used to effect the change.
The use of chemicals to control certain groups of plants has some unique features:
1. All herbicides used in forestry are selective in some important way.
2. Herbicides do not cause physical injury to preestablished trees, resistant plants, animals, or
soils.
3. Herbicides usually have minimal impact on water quality, with no siltation problems nor
complete exposure of water to sun.
4. Chemical control leaves protective cover for wildlife while frequently enhancing the nutri-
tive value of resistant plants and pioneer species.
5. Dead plants may temporarily constitute a continuous fuel supply in some circumstances;
hence herbicides may increase the fire hazard briefly.
6. Certain herbicides may influence the metabolism of some plants and thus make them more
or less vulnerable to pest activity.
7. Aerially applied herbicides may not respect boundaries.
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On balance, herbicides are a very potent tool in ecosystem management. They permit the
accomplishment of forestry tasks that would be postponed indefinitely if mechanical or labor-
intensive methods had to be used. The important advantage that herbicides may be applied quickly
may, however, allow errors of planning or application that are not identified until the job is com-
plete. Like any other tool, they are subject to misuse and must be carefully controlled.
Mechanical Control. —Mechanical control as discussed here relates to practices involving power
equipment for vegetation control. These are used primarily where total vegetation eradication is
desired; occasionally, selective felling is used where desirable trees are established, as in precommer-
cial thinning.
Control is achieved by uprooting, chipping, or knocking down vegetation. The least intensive
practices involve bulldozers that flatten woody plants without removing them. The most intensive
includes chopping of brush and incorporating the chopped material into the soil. All practices of
this type leave the site in a less disturbed condition than does an agricultural plow, but in a substan-
tially more disturbed condition that that produced by herbicides alone.
Comparison between mechanically and herbicidally prepared sites indicates that they do not
accomplish the same thing in the short term, but they may both support the same long-term objec-
tives. Mechanical clearing exposes mineral soil extensively. Mineral soil provides seedbeds for
abundant herbaceous growth as well as woody plants. The mixture of herbs and shrubs tends to
compete severely with planted trees and to provide abundant forage. In the presence of adjacent
cover, the habitat for deer is one that supports maximum numbers of animals. The effect of animal
use is frequently so severe as to stabilize cover, including planted trees, in a browsed-down, pasture-
like condition. Enhancement of deer habitat, however, is accompanied by changes in cover for
many small mammals, hares, and rabbits. Some species may benefit; some may decline (Lawrence,
1967; Borrecco, 1973).
Mechanical methods have both advantages and disadvantages. Any conventional bulldozer can
do the job, but some special equipment can improve efficiency. Physical obstacles to reforestation
are removed, which reduces problems in planting operations (Bentley, 1967). The results of the
operation are easy to perceive: no toxic substances are involved. The most serious disadvantages are
those of physical disturbance and cost. If total ecosystem impact is considered, this practice may
have important effects on virtually every component. Whether these effects are judged to be benefi-
cial or detrimental depends on management objectives. The exception to this is the increase in soil
mobility associated with scarification. In addition to erosion potential on steep slopes, soil redistri-
bution may also cause local nutrient deficiencies.
The disturbance of surface soil creates a receptive seedbed. In some areas rapid revegetation is
needed for surface stabilization; in others competition and animal use are excessive. Achievement of
exactly the appropriate amount of cover is very difficult to manage.
Fire.— Removal of vegetative competition by burning is an important practice in forestry, espe-
cially in the Southeastern United States. Periodic burning is a natural phenomenon in many light-
ning-prone areas. Under evolutionary pressure, fire-resistant species (e.g., southern pines) were
naturally abundant primarily because of repeated fires. Exclusion of fire has led to increasing
abundance of ground cover and decreasing regeneration (USDA, 1965). Maintenance of conifer
forests has come to depend very heavily on the control of hardwoods, with fire, herbicides, or
mechanical eradication being the predominant tools.
The utility of controlled fires depends on accumulation of fuel and suitable burning condi-
tions. The fire must consume the fuel, yet do so with an intensity that does not damage the trees.
This requires burning every few years to avoid fuel buildup; no other practices depend on repetition
in this way.
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The unique effects of fire as a vegetation control method include the following:
1. Fire favors the survival of heat-resistant trees and the germination of seeds stimulated by
heat.
2. Fire eliminates accumulations of fuel without soil disturbance, provided slopes are moder-
ate and fire intensity is low.
3. Burning of forest debris releases some nutrients for rapid uptake by pioneer vegetation; the
resulting growth tends to be lush and of high nutritive content for wildlife.
4. Fires tend to cause violent death to certain groups of nonburrowing animals, even though
survivors may have a substantially improved habitat.
Some of the above features are important in the applications of fire as a substitute for herbi-
cides or other control techniques. Problems of smoke control, animal escape, and national antipathy
to forest fires limit free use, however. Furthermore, the prevention of fires for extended periods
allows fuel to accumulate through natural processes, so that controlled burning is no longer feasible
in many areas.
A new application of fire involves a combination of herbicides and fire. The so-called brown-and-
burn technique is sometimes used for preparing a total brushfield for planting. The method allows
for the desiccation of fuel without the physical disturbance of bulldozing or cutting. When the
green brush has dried out, it can be burned when burning conditions on unsprayed areas prevent
spread outside the prescribed area. This practice has the advantages of both burning and herbicides.
Applied in small units, it has the advantages of allowing animal escape, incinerating residual herbi-
cides, and reducing smoke emission. Cost, in general, is equal to or less than that of scarification,
and there are instances where the prospect of plantation survival and growth are close to optimal for
this technique.
No Vegetation Control.—Commercial forest species almost invariably cast sufficient seed to
provide for adequate regeneration. The presence of several million acres of unregenerated cutover
land in the Douglas-fir region alone is testimonial to the stability of untreated vegetation that has
been allowed to develop to the exclusion of conifers. Gratkowski et al. (1973) have identified vege-
tation in the forms of herbs, shrubs, and noncommercial hardwoods as responsible for extensive
regeneration failures. Of five major timber-producing states in the East, land supporting well-
stocked stands of desirable species accounted for only 1 to 9 percent of commercial forest area,
whereas 69 to 86 percent of the forest area was occupied by trees of marginal value. On most of
this, only planting or stand conversion will improve production status (USDA, 1965). Prospects for
natural reemergence of native coniferous forest types are virtually nil within the lifespan of a human
being. The unpromising status of the hardwood forests in the Eastern United States is due to a his-
tory of selective cutting that has left mature trees of no value (to the owner) to form the dominant
forest cover. This condition is virtually permanent, in the context of present economic models,
without some cultural practices to restore original composition.
Forest-inventory data for forested regions of the United States describe a reasonably large
growth for the poor hardwood forests of the East. They also point out that much of the wood is of
poor quality and marginal salability (USDA, 1965). This consequence of "no control" provides
abundant evidence that not killing undesirable plants has a prolonged economic and ecological ef-
fect. Nearly all the lands so described once supported valuable stands. In no documented instance
has a history of "high-grade" harvesting of trees decreased the productive capacity of the land. Thus
the consequences of no control are not reflected in the productive capacity of the land, but only in
the utility of the existing tree cover and the long timespan involved in natural reversion to original
conditions.
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Environmental Perspective of Control Practices—Do They Accomplish the Same Thing?—The
choice among alternative methods of vegetation management has implications from the standpoint
of both intermediate and end objectives. Chemical and nonchemical controls function in different
ways. They have in common only the killing of above-ground portions of undesired woody plants to
promote growth of some desirable vegetation. If both methods succeed in establishing their objec-
tive vegetation type, they have both achieved their long-term goals on a similar basis. In the short
term, however, there are consistent differences.
Typically, herbicides do not eradicate all woody plants. The mixture of living and dead plants
provides abundant food and cover for big and small game, and adequate perches remain for preda-
tory birds. Eventually, crop species become dominant, and the game habitat is then controlled by
the ability of understory forage species to persist under crop-tree dominance. Changes in species
composition are achieved without physical disturbance either to animals or soil. At no time is the
living complex of plants so completely suppressed that nutrient losses are likely, although complete
eradication does carry this hazard (Likens et al, 1970). Fears of toxicity to animals appear to be
unwarranted when herbicides are used as recommended (Brown, 1967; Morris, 1971).
The achievement of long-term goals by the physical removal of vegetation has a substantial
disrupting influence on an ecosystem. The soil is disturbed and may be compacted by working
moist soil. Animal habitats are more completely changed than they are when herbicides are used,
but forage is still greatly increased for some species and decreased for others. The microenvironment
for planted tree seedlings is characterized by more sunshine, more herbaceous competition, and
more severe moisture stress. The enhancement of seedbed conditions for shrubs and herbs some-
times results in the establishment of a competitive cover that requires herbicide treatment to release
trees from suppression by competitors. There is no toxic effect from physical removal. However,
the physical disturbance has a greater total impact on animal life than does the use of herbicides.
In perspective, the preceding comparisons of physical and chemical removal of vegetation may
be viewed in relation to ordinary agricultural practice. The act of plowing and growing an agricul-
tural crop repeatedly constitutes a chronic maintenance of ecosystems in a disturbed state. None of
the forest practices maintains the chronic stress; the long-term objective of rehabilitation is, in ef-
fect, to relieve stress. The infrequency of herbicide application or related forest practices and the
low percentage of total forest area that will ever be re-treated under management indicate the
limited nature of the national scope of problems resulting from the use of herbicides for forest re-
habilitation. However, the long-term effect of not using herbicides or other rehabilitation methods
will be widespread and will downgrade both economic and aesthetic values.
Premise II: Forest practices supporting the management of any specific resource should be
considered relative to their impacts on other uses and values.
This premise is based on the following assumptions:
1. The public has an interest in the long-term perpetuation of all forest-resource values.
2. Long-term considerations outweigh short-term expedience in resource management.
3. The economic return from the dominant forest use(s) may be necessary to maintain the
entire complex of forest resources on any given ownership.
Approaches to Resource Management Relevant to Herbicides.—Every forest practice has some
impact on all forest values—some positive, some negative, and many so small as to be insignificant.
Impacts are viewed differently by owners and nonowners, depending on economic interests and
personal points of view. In forests, especially, nonowners are prone to pass judgment on manage-
ment and to consider mismanagement by their own definitions a public issue. Private ownership
accounts for nearly three-fourths of the commercial forest land in the United States. The issues
84
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related to the long-term maintenance of resources on all forest land are of public significance. Those
related to forest management within the confines of specific ownership and not affecting long-term
resource maintenance are largely of personal or academic interest. This discussion therefore presents
the impacts of forest practices relative to their duration and according to classifications that can be
separated according to their public or personal significance.
Table 1 illustrates the effect of tree establishment and maintenance practices on various public
and private forest-resource values. Timber is the primary economic value to the private owner; water
quality and yield are of general public interest but of little economic importance to private owners.
Game resources are of interest to the public, but on private lands game resources are only tolerated
by the owners. Aesthetic values are of general interest, but they may actually be of negative value to
private owners because of their effects on valuation and taxation. Thus the regulation of practices
to a particular end is likely to increase values to one interest group at the expense of another. The
effect of regulating practices so that the owners' forest-management options are reduced is likely to
have a long-term effect on resource values of all kinds; departure from forestry uses of land will
have a greater impact than will almost any of the methods used in the perpetuation of forests. Much
of the pressure to regulate is from the urban-oriented public. Responsiveness to such pressure can be
adequate only if there is a reasonable understanding of tradeoffs involved in any action.
The listing of impacts in Table 1 includes reasonable generalizations. Exceptions can be made
to some of them on an individual basis, which is merely evidence of the great variability of forest
conditions within this nation. Such exceptions are attributable, in part, to unusual environmental
conditions requiring special management. More frequently, the exceptions result from the misappli-
cation of a soundly advised practice. Such exceptions can occur with every practice, however, and
are perhaps less likely to occur with herbicidal than with nonherbicidal methods.
Premise HI: Long- and short-term hazards to the environment are significant in any selection
among forest-management alternatives.
The term "hazard" is defined here as opportunity for damage to environmental factors and
values. In this discussion the following assumptions are made:
1. Hazard is real only under circumstances where a practice sets up a condition where damage
can occur as a direct result and where the probability of such damage is great enough to justify con-
cern.
2. Choices among management alternatives all involve choices among hazards, with none of
the alternatives offering a no-hazard choice.
3. Priorities in methods, and hence in hazard selection, are based on human safety, resource
maintenance, economics, and extra-management fringe benefits, in that order.
Herbicide-related hazards will therefore be discussed in terms of the usage of the various types
of chemicals, the behavior of the same compounds in the forest system, and the relation of hazard
associated with such behavior to hazards related to nonherbicidal methods.
Herbicides Used in Forestry.—The enormous range of job specifications for herbicides requires
a broad range of chemical properties. Basically, these compounds can be classed according to usage,
persistence, and relative toxicity. They are used as soil treatments, foliage sprays, or injection fluids.
Persistence ranges from moderate to short in the general context of pesticides. The toxicity of most
herbicides used in forestry is in the range of moderate to low (Warren, 1967). Many materials are
useful for more than one purpose, particularly those suitable for injection and foliage application.
The general characteristics discussed below are consistent within forest-use classifications.
85
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Compounds used specifically for their soil activity tend to be low in water solubility and are
prepared for this use largely as wettable powders or granules. They are suspended in water or ap-
plied dry. Those in general use are nonvolatile and are nearly immobile in soil. All are low in toxic-
ity to mammals and have half-lives of 1 to 6 months (Anon., 1972).
Foliage-active materials include almost all other compounds used in forestry. They may be
either soluble or emulsifiable in water. Those that emulsify in water are generally completely solu-
ble or miscible in oil. Many that are soluble in oil are neither emulsifiable nor soluble in water and
are formulated specifically for oil-borne bark sprays. The addition of an emulsifier may make them
directly comparable to any other emulsifiable material of other similar properties. Water-
emulsifiable herbicides may be mixed with either water or oil, or a mixture of oil and water. Water-
soluble compounds are almost never miscible or emulsifiable in oil and are used solely in water.
These compounds range from moderately volatile to nonvolatile and from moderately leachable to
tightly adsorbed. Persistence is variable, with the reported half-lives ranging from 1 week to 6
months. Toxicity to mammals ranges from moderate to low (Anon., 1972).
Herbicides formulated for injection must be water soluble. These materials are used as undi-
luted concentrates and are usually provided with surfactants that cause them to soak into a moist
woody surface exposed by a fresh cut. Virtually all of these herbicides have foliage activity; a few
are used on soil or foliage and as injection fluids. These materials are generally used in a manner that
isolates them from the general environment in reforestation. Persistence in this isolated application
is not known, nor is the hazard to mammals.
The compounds discussed below are grouped and described in relation to forestry use. This
material was abstracted from Newton (1969) and the Dictionary of Pesticides (Anon., 1972).
Soil-Active Compounds.— Amizine is a mixture of amitrole (3-amino-l,2,4-triazole) and
simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) in the ratio of one part amitrole to three parts
simazine. Its uses and application rates are similar to those for atrazine, except that amizine has
more ability to suppress established perennials, including desirable species exposed to the spray.
Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is used in early spring at rates of
3 to 5 pounds of 80 percent product per acre in 5 or more gallons of water. This compound is very
selective in confier plantations, even when applied broadcast after planting. Atrazine is the most
common herbicide used for herbaceous weed control in conifer plantations. Very popular with
Christmas tree growers, it often produces rapid growth and a deep blue-green color in conifers. Atra-
zine may be mixed with 2,4-D, with general broadening of the weed-control spectrum. Its residual
activity is generally limited to one growing season. It can cause damage to crop trees in light soils
and with heavy rainfall.
DCPA (dimethyl tetrachloroterephthalate) has little general use for field application in forestry.
In some experiments it has been shown to have good selectivity for weed control in nursery beds.
Fenuron (3-phenyl-l,l-dimethylurea) is the only common forest-brush-control herbicide that
depends exclusively on soil activity. It has been used with success particularly on moderate- to
coarse-textured soils in plantations of southern pines. It selectively kills hardwoods in southern pine
plantations. Its residual activity may last more than 1 year.
Dalapon (2,2-dichloropropionic acid) is the only water-soluble, soil-active compound in com-
mon use for herbaceous weed control in forestry. It is used as a grass killer in plantations at rates of
4 to 10 Ib/acre. It is often combined with triazines and 2,4-D. Dalapon has a short residual life and
has low mammalian toxicity.
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Simazine has uses similar to those for atrazine, except that it has a much lower solubility, is
more strongly adsorbed in the surface soil, and is less effective on resistant perennials. Generally,
simazine requires heavier rates of application than does atrazine (3 to 8 Ib/acre) and is more expen-
sive than atrazine for any given degree of weed control. However, simazine may be somewhat more
selective at high dosage rates than atrazine. Some residual activity may be observable 1 year after
application. It is well suited for light soils in areas of high summer rainfall. Toxicity to mammals is
low.
Substituted uracils, carbamates, and many other soil-active herbicides are not applicable for
general use in forest plantations. Local trials may demonstrate selectivity sufficient for economic,
safe weed control in particular combinations of soil, vegetation, and crop species. Since many such
compounds have not been tested in forestry, their potential is not known.
Foliage and Stem-Applied Brush Killers.—Amitrole has an action unique among the brush kill-
ers. Its uptake is mostly through foliage, and its action is through the destruction of chlorophyll
material in the tissues of weed leaves. Amitrole is necessarily applied during the foliage season—and
in a water carrier. It is frequently used at rates of 1 to 4 Ib/acre in 10 or more gallons of water. Ami-
trole is extremely effective against certain shrub species, particularly members of the blackberry
group. It has the drawback of being quite damaging to most conifers, although selectivity at rates of
1 to 1.5 Ib/acre has been found. Its degradation in the soil is rapid. Although low in acute toxicity,
amitrole has been reported to have carcinogenic properties.
Ammate (ammonium sulfamate), as distinguished from the fertilizer ammonium sulfate, has an
extremely high degree of toxicity to plant foliage. It is relatively nonselective and kills weeds and
brush alike through foliage uptake and translocation. Common solutions for use involve 1 to 4
pounds of ammate per gallon of water applied to the point of dripoff. Notwithstanding its general
effectiveness, this material is quite expensive for general broadcast herbicide use. It is highly corro-
sive, low in toxicity, and has a short residual life.
Brush killer is a half-and-half mixture of 2,4-D and 2,4,5-T used to control general mixtures of
brush species. The mixture is cheaper than 2,4,5-T alone and is effective on some species that are
sensitive to 2,4-D without the high cost of the 2,4,5-T spray. It probably does not have a much
broader range of action than 2,4,5-T alone, but its use is frequently justified on the basis of cost. It
has not always been observed that the 2,4-D and 2,4,5-T actions are fully complementary (see 2,4-D
and 2,4,5-T for specific behavior).
Picloram (4-amino-3,5,6-trichloropicolinic acid) has extreme foliage activity in woody plants.
Effects are produced through root uptake; it is also used for injection. It is capable of controlling
many species resistant to 2,4-D and 2,4,5-T. Its cost is high, however, and its residual action on
conifers can be detrimental. It is nonselective in mixed conifers and hardwoods. Special techniques
for application must be devised before picloram can be generally recommended for use in forests. It
is formulated in ways similar to 2,4-D or 2,4,5-T. The solvent in which it is used is usually water.
The rates of application are normally 0.5 to 2 Ib/acre for general brush control in a low volume of
water or up to 2 pounds per 100 gallons in a broadcast high-volume treatment. Picloram is classed as
moderately persistent, with residual effects persisting 6 to 12 months. It is one of the more mobile
herbicides in soil, although damage resulting from mobility appears to be limited with forest appli-
cations. It is low in acute mammalian toxicity.
Silvex [2-(2,4,5-trichlorophenoxy)propionic acid] is very closely related to 2,4,5-T and is used
in some situations where species resistant to 2,4,5-T are the dominant brush species. Its superiority
to 2,4,5-T for multiple-species control has not been amply demonstrated, and the merits of Silvex
over 2,4,5-T are usually insufficient to justify the additional cost. When used as a basal spray, in an
oil solution, Silvex is specifically active against maples and perhaps other species. Its persistence and
toxicity are slightly greater than those of 2,4,5-T; rates used are the same.
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2,4-D (2,4-dichlorophenoxyacetic acid) is normally formulated as an amine, emulsifiable acid,
or ester for effective brush-control work. This material is effective against many broadleaf herbs and
some susceptible trees and shrubs like alder and willow. 2,4-D is low in cost and is high in effective-
ness for susceptible species. In addition to its effectiveness on brush, it is also highly effective for
increasing control of broad-leafed herbs not killed readily by atrazine. 2,4-D is damaging to conifers
during the growing season, but not during the dormant season at moderate rates. Some pines are
sensitive during early spring, particularly with oil solutions or emulsions. For broadcast application
2,4-D is usually used at rates of 0.5 to 4 Ib/acre, depending on sensitivity of weeds and methods of
application. During the dormant season the ester formulation is usually dissolved in oil or suspended
in an oil-water emulsion for brush control and emulsified in water alone for herbaceous weed con-
trol. Amine formulations are used undiluted for injection of some species, but seldom for brush
killers. The residual life of 2,4-D is short; the toxicity is moderate. Some esters are especially toxic
to fish.
Very similar to 2,4-D in its action and uses is 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). This
material is more effective on many hard-to-kill woody species than 2,4-D; rates used are comparable
to those of 2,4-D. Some species not controlled by either compound separately are killed by a mix-
ture (brush killer). 2,4,5-T by itself and in mixture with 2,4-D is the most common phenoxy herbi-
cide in use for general brush control in reforestation. Many forest species are not controlled at all
well by 2,4-D, and the use of 2,4,5-T is advised where such 2,4-D-resistant species are common and
where they interfere with forestry objectives. The residual life of 2,4,5-T is intermediate between
that of 2,4-D and picloram, although activity in soil is slight. Acute mammalian toxicity is moder-
ate; some esters are especially toxic to fish.
Herbicides Best Adapted for Injection.—Cacodylic acid (dimethylarsinic acid) is used to con-
trol conifers and numerous phenoxy-resistant hardwoods. Recommended rates are from 0.25 to 0.5
gram per inch of tree diameter, formulated as a concentrated salt solution. Cacodylic acid is thought
to metabolize into materials that are apparently toxic or disagreeable to insects, and the incidence
of insect attack following treatment with this material is less than would be expected for trees felled
with a power saw. This material is subject to seasonal variation in effectiveness, with optimum use
during seasons when most nonarsenicals are ineffective. Cacodylic acid is tightly bound to organic
material and soils. It is not known how long it remains in the ecosystem, but there is evidence that
it becomes biologically inactive within days. Microbial degradation has been reported, but kinetics
are not yet known (Newton and Holt, 1971; Woolson and Kearney, 1973). Acute mammalian toxic-
ity is moderately low.
MSMA (monosodium methanearsonate) is used in a manner similar to cacodylic acid for tree
injection work. This material has shown greater activity than cacodylic acid on several species; it
appears to be metabolized in the same way. The presumed metabolite may also be involved in
suppression of insects in treated trees. MSMA has the advantages of low cost and of activity on
some hardwoods for which cacodylic acid is not specifically active. It can also be used for chemical
debarking and preharvest timber drying. MSMA is thought to behave in a manner similar to caco-
dylic acid; both are of moderate toxicity. The organic arsenicals may well provide opportunities for
noninsecticidal control of bark beetles in conifers (Newton and Holt, 1971) and for nonfungicidal
control of some root rots (Laird and Newton, 1973). These properties are probably unique to these
herbicides.
Picloram is used for injection in conifers and in maples for both stand improvement and pre-
commercial thinning. This material is mobile in the soil and in the translocating tissue of the trees; it
is known to travel through root grafts and via exudation into the soil. Treatment of one species may
promote the development of symptoms in other species. Picloram controls a broader spectrum of
species by injection than any other known compound, and some drawbacks to its use may be justi-
fied on account of extreme effectiveness under some conditions. Picloram is used at low dosage
rates for tree injection.
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2,4-D amine, the common agricultural chemical used for killing dandelions and other sensitive
weeds, is appropriate for spring and summer injections in oaks, willows, and alders. In contrast to
the ester formulations, which are used for foliage and stem sprays, a water-soluble amine is essential
for proper uptake and translocation after injection. 2,4-D amine is not effective in some species like
conifers and maples. This material is always used undiluted. Effectiveness is greatest during the
period of full leaf, although it is sometimes effective for winter usage. More injection is done with
2,4-D amine than with all other compounds combined.
2,4,5-T amine is comparable to 2,4-D amine in formulation. This material is more effective on
some woody species than 2,4-D. Its superiority to 2,4-D is limited, however, and it is not widely
used because of cost.
Application Techniques.—Herbicide application methods in forests have some unique features.
Broadcast treatments are often applied by special equipment adapted for tall-brush or drift control.
Individual tree treatments are found only in forestry practices; such treatments are necessary for
killing large cull trees not killed by aerial treatment and for individual-tree selection for stand im-
provement.
Broadcast—Broadcast applications of herbicides include coverage of the crop species. Volumes
of 1 gallon to several hundred gallons per acre may be applied, but special equipment is required to
get good coverage with volumes below about 10 gal/acre. Very low volumes require extremely small
droplet size and high concentrations of active ingredients, a combination that lends itself to extreme
drift hazard. Inherent in the high drift potential is the loss of herbicide before it reaches its target.
This factor tends to discourage the use of very low volumes except in special circumstances. On the
other hand, the excessively high volumes create serious problems of supply and excessive runoff of
active ingredients. Volumes of less than 5 and more than 20 gal/acre are seldom applied aerially;
ground rigs usually apply 100 gal/acre or less. Most broadcast sprayings of herbicides used in for-
estry are applied aerially in areas remote from croplands.
Treatments of Individual Trees.—Chronic difficulty is experienced in controlling large cull
hardwoods in forests. Basal treatment has been one of the most effective and consistent methods of
killing such trees. Backpack sprayer equipment is used, and treatments are applied simply by spray-
ing around the basal few inches of the trees. A soaking solution of ester formulations of phenoxy
herbicides in diesel fuel is usually used. Picloram has recently become available in ester formula-
tions; this procedure is costly but effective. There are no known hazards other than those in han-
dling the herbicide concentrates.
Concentrated herbicides may be used in small quantities in spaced cuts made in bark of trees.
Cuts into which the herbicide is placed may be made with special tools or injectors. Injectors may
take the form of hatchets or long hypodermic-type instruments with chisellike bits on the lower
ends. Hatchets and oil cans are suitable for small jobs with a low investment, whereas injectors im-
prove the speed of operation considerably when many trees are to be treated or the terrain is diffi-
cult.
Improvements in chemical technology have now provided a wide selection of compounds suita-
ble for injection. Some of these compounds are so effective that very small volumes in widely
spaced cuts provide adequate tree-killing capacity. The small volumes of herbicides necessary to
accomplish a given job with injectors mean that refills are infrequent and labor costs for transport-
ing materials are minimal. Tree injection lends itself well to precommercial thinning, hardwood con-
trol, and stand-improvement treatments in which both conifers and hardwoods may be controlled in
the same operation. Amounts of herbicide used are small, and general environmental contamination
is avoided with this method. Injection is presently the most selective and appropriate method for
widespread forest-weed problems in the United States.
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Hazards of Herbicide Use.—Herbicides are biologically active compounds. Despite their ex-
treme activity in plants, however, their toxicity to insects, mammals, fish, and birds is usually much
lower than that of insecticides. In terms of their effects on wildlife and fish, most herbicides should
not be classed with the extremely toxic pesticides about which considerable alarm has been raised.
Their relative safety notwithstanding, it is difficult to control the distribution of herbicides by aerial
application. The rough topography common in forest areas tends to reduce the precision of applica-
tion. Herbicides, although not normally toxic to mammals, come in contact with various organisms,
including people. The effects of such contact warrant attention.
Stream Contamination.—Herbicides used in large quantities on large areas of forest land may
find their way into watersheds. Considerable research has been conducted to determine the amount
of herbicide present in streamflow at a given time after aerial application of herbicides over a
stream. It has been found that direct application to the water surface is necessary for appreciable
amounts of herbicide to get into streamflow. Even when open streams flow through spray-project
areas, the degree of contamination is minor, particularly when the application falls on fast-moving
water (Morris, 1967). Exclusion of open watercourses or streams 10 feet wide or more should en-
sure adequate safety, especially during the dormant season. Water usage from streams exposed dur-
ing the growing season warrants close attention, however.
The amount of contamination from small streams receiving direct spray is very small and per-
sists only briefly. Studies in the Pacific Northwest indicate that broadcast application during the
dormant season is likely to produce peak concentrations in open waters, within projects, ranging
below 1 ppb per pound of phenoxy herbicide per acre for each percentage of the watershed treated
(Norris, 1967). There is no evidence that fish and food-chain organisms suffer seriously from
phenoxy herbicides as applied in forest spray operations. Even in the summer, when streams are
moving slowly, the main factors to be avoided are spraying directly into ponds, pools in slow-
moving streams, and long, continuous stretches of open water. Such conditions are encountered
infrequently in midsummer in the forest, however, and hence contamination tends to be a very
localized problem. The maximum stream contaminations reported in forest spray operations have
been substantially lower than published median tolerance limits for fish; furthermore, such concen-
trations are also observed to be short in duration (Tarrant and Norris, 1967).
In connection with 2,4,5-T, dioxin is a present concern. The present industry standard of a
dioxin concentration of 10~7, combined with normal operational stream contamination of 10~8 or
less of 2,4,5-T as a maximum, indicates a peak dioxin concentration of 10"15 or less.
Livestock and Herbicide Residues.—Many herbicides used in forestry are permissible for use on
agricultural crops on a "no-residue" basis. Farmers have expressed concern that livestock would
stray on sprayed lands with the subsequent possibility of condemnation of meat. This problem is of
special concern on open-range lands in the Western United States.
Most herbicides are metabolized readily or eliminated by livestock. Cattle and deer eliminate
herbicides of the phenoxy and triazine groups without obvious toxic symptoms, when the herbi-
cides are administered at dosages equal to or greater than those to be expected from browse in
treated forests (Newton and Norris, 1968; St. John, 1964). Detection methods have become so
sensitive, however, that minute amounts of herbicide may be detected now that were not detectable
when the no-residue limit was originally established. Such residues are not construed as harmful, but
should be recognized in terms of joint responsibilities of forest and livestock owners.
Drift Damage.—Herbicide movement through the atmosphere from a treated zone to sensitive
crops and ornamentals has been a serious problem in agricultural operations. Many of the broadcast
herbicides are applied in forests during the dormant season, when very few crops are sensitive. Never-
theless, aircraft normally fly higher in forest operations than over croplands, with an increased prob-
ability of drift of vapors and fine droplets. During seasons when crops or ornamentals are subject to
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damage, forest operations can cause drift damage at considerable distances. Much work has been
done to reduce the likelihood of occurrence, however, and methods have been developed for drift
management. The following steps will minimize the expectation of drift damage:
1. Spray near agricultural lands during the dormant season when possible
2. Ensure that the operation is well flagged
3. Never apply herbicides when the wind velocity will cause major movement of herbicide
spray patterns or when the direction will cause drift toward susceptible crops or ornamentals
4. When using esters, use only low-volatility formulations when temperatures are likely to
exceed 70° F; oil-soluble amines are nonvolatile and perform similarly to esters in controlling brush
5. Where feasible use tree injection along boundaries
•
6. Drift-control formulations and equipment are available for projects that offer prospects of
drift damaep
Conclusions
Most biological problems in forestry lend themselves, in some way, to solution with herbicides.
Insects, diseases, and inadequate allocation of productive capacity to salable species are environ-
mentally linked problems. Fortunately, improvement of crop tree habitat tends to discourage some
weeds, diseases, and insects. Inexpensive and selective herbicides permit forest managers to cull
stands to discriminate against diseased and infested trees, releasing valuable crop trees at the same
time. These uses of herbicides are ecologically sound.
Herbicides can cause great destruction. In the case of some herbicides, as little as 1 Ib/acre can
kill most living trees in a bulky and complex forest. Such destructive power must not be regarded
lightly. On the other hand, the potential for creative use of these materials has provided landowners
with an exciting new opportunity for accomplishing their objectives in forestry. The possibilities for
damage are generally well documented. However, by optimizing the balance of benefits over
hazards, herbicides can be used beneficially to replace many practices of known adverse environ-
mental impact.
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REFERENCES
Anonymous, 1972. Dictionary of Pesticides, Meister Publishing Co., Willoughby,
Bently, J. R. 1967. In: Herbicides and Vegetation Management in Forests, Ranges, and Noncrop
Lands. Oregon State University School of Forestry, Corvallis, Oreg.
Benzie, J. W., Little, S., and Sutton, R. F., 1973. J. Forestry, 71(3), 154.
Black, H. C. (ed.), 1974. Wildlife and Forest Management in the Pacific Northwest, Oregon State
University School of Forestry, Corvallis, Oreg.
Borrecco, J., 1973. "The Response of Animals to Herbicide-Induced Habitat Changes," Master's
thesis, Oregon State University, Corvallis, Oreg.
Brown, E. R., 1967. In Herbicides and Vegetation Management in Forests, Ranges and Noncrop
Lands, Oregon State University School of Forestry, Corvallis, Oreg.
Fitzgerald, C. H., Peevy, F. A., and Fender, D. E., 1973. J. Forestry, 71(3), 148.
Gratkowski, H., Hopkins, D., and Lauterbach, P. G., 1973. J. Forestry, 71(3), 138.
Gratkowski, H., 1967. In Herbicides and Vegetation Management in Forests, Ranges and Noncrop
Lands, Oregon State University School of Forestry, Corvallis, Oreg.
Laird, P. P., and Newton, M., 1973. Plant Disease Reporter, 57(1), 94.
Lawrence, W. H., 1967. In Herbicides and Vegetation Management in Forests, Ranges and Noncrop
Lands, Oregon State University School of Forestry, Corvallis, Oreg.
Likens, C. E., Bormann, F. H., Johnson, N. M., Fisher, D. W., and Pierce, R. S., 1970. Ecol.
Monogr., 40(1), 23.
Newton, M., 1971. In Pest Control, Pesticides and Safety on Forest and Range Lands, Oregon State
University Division of Continuing Education, Corvallis, Oreg.
Newton, M., 1973a. J. Forestry, 73(3), 159.
Newton, M., 1973b. "Regional Distribution of Vegetative Pests and Control Practices in the United
States, and Their Impact on Productivity," unpublished report to the National Academy of
Sciences Environmental Studies Board, Study on Pest Problems, Forest Study Team.
Newton, M., and Holt, H. A., 1971. J. Econ. Entomol., 64(4), 952.
Newton, M., and Norris, L. A., 1968. InProc. Western Weed Control Conf., Boise, Idaho.
Norris, L. A., 1967. Chemical Brush Control and Herbicide Residues in the Forest Environment,
Symp. Proc., Oregon State University School of Forestry, Corvallis, Oreg.
Norris, L. A., 1971. J. Forestry, 69(10), 715.
St. John, L. E., Jr., 1964. J. Dairy Sci., 47(11), 1267.
Tarrant, R. F., and Norris, L. A., 1967. In Herbicides and Vegetation Management in Forests,
Ranges and Noncrop Lands, Oregon State University School of Forestry, Corvallis, Oreg.
USDA, 1958. Timber Resources for America's Future, Forest Resource Report 14, U.S. Depart-
ment of Agriculture, Washington, D.C.
USDA, 1965. Timber Trends in the United States, Forest Resource Report 17, U.S. Department of
Agriculture, Washington, D.C.
Walker, C. M., 1973. J. Forestry, 71(3), 136.
Warren, L. E., 1967. In Herbicides and Vegetation Management on Forests, Ranges and Noncrop
Lands, Oregon State University School of Forestry, Corvallis, Oreg.
Woolson, E. A., and Kearney, P. C., 1973. Environ. Sci. Technol, 7(1), 47.
GRAZING LANDS
Introduction
Almost half the total land area of the United States is used for grazing purposes. Weeds and
brush infest nearly all these forage lands and are a serious problem on a high percentage of them.
Economic losses from weeds on foragelands include low yields of forage and animal products per
unit area, livestock poisoning, reduced habitat values for many species of wildlife, reduced ground-
water yield, increased costs of managing and producing livestock, and increased frequency of new
seeding failures (Klingman, 1970).
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Trends toward dominance by weeds can be halted or changed by the judicious use of mechani-
cal or herbicidal control methods, introduction of new forage-plant species, fertilization, and con-
trol of the kinds and numbers of grazing animals and their season of use. Some grazing lands do not
respond readily to improvement measures because of such factors as climate, native animal life,
plant species, low soil productive capacity, or erosion. Nevertheless, many foragelands can be made
more productive by present techniques, which often include some form of weed control.
Efforts to correct weed and brush problems in foragelands have been minimal. Almost every
year there is an increase in the scope of the problem. Future research undoubtedly will improve
control methods; however, we already know enough to be doing far more in this field.
Weed competition is a particularly frequent and serious problem during the establishment of
new stands of forage crops from seedings. The slow growth of the forage seedlings provides oppor-
tunity for rapidly growing weeds to overtop and severely shade them or to exhaust the moisture
supply in the soil before the forage-seedling root system is well developed. The control of weeds
often makes the difference between success and failure in such seedings (Klingman, 1970).
Scope of the Weed and Brush Problem.—Brush infests 320 million acres of the almost 1 billion
acres of land used for grazing in the continental United States (Sampson and Schultz, 1957). In
addition, poisonous and other herbaceous weeds are found in all grazing lands—they are abundant
on ranges in poor condition but less so on ranges in good condition.
The estimated loss resulting from brush and weeds in $237,000,000 on rangelands and
$396,000,000 on pasture lands. This is based on an estimated loss in yield of forage of about 13
percent in the western half of the United States and 20 percent in the humid Eastern States
(LeClerg, 1965).
During 1968, over 9 million acres of grazing land were sprayed with herbicides at a cost of
$36.2 million. Of this acreage, about 4.4 million were rangeland and 4.7 million were pasture.
Farmers or ranchers used their own equipment to spray only 17 percent of the rangeland but 74
percent of the pasture. Commercial applicators treated the remainder in each case.
The cost of spraying rangeland is higher than the cost for pastures mainly because relatively
more brush species on rangelands were sprayed with 2,4,5-T. The less expensive 2,4-D is effective on
many pasture weed species and is more commonly used on pastures. Also, the rate of herbicide re-
quired to control brush is usually higher than that needed to control herbaceous weeds (USDA,
1972).
Nature of the Problem.—Weed control in pastures and rangelands involves special problems.
The forage frequently consists of many plant species, including many species of grasses intermixed
with other desirable species such as legumes and browse. The forage species are interspersed with
undesirable woody plants and other weeds. Selective elimination of the undesirable species is a pre-
requisite to upgrading the range vegetation. Subsequently, competition from the desirable vegeta-
tion is needed to minimize reinvasion. Herbicides with a sufficiently broad spectrum of efficacy to
kill many types of weeds and brush frequently eliminate some of the desirable forage species as
well. Also, some weeds are resistant to a weed-control treatment. These resistant species tend to
spread when the treatment kills other competitive weeds.
The complexity of the weed-control problem is indicated by a survey conducted in!965
(USDA, 1968). There were 147 weed species listed among the "five most important weeds" on pas-
tures and haylands in the various states responding to the survey and 105 species listed on range-
lands. These weeds include grasses and broadleaf species that were annuals, perennials, and woody
plants. Control procedures for these various types are quite different.
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The invasion of weeds and brush, and conversely their control, results from the interplay of
myriad environment, soil, plant, animal, and climatic variables. Thus it is important to integrate the
chemical, cultural, and management systems of weed control with the management practices re-
quired to produce high-quality forage for animal consumption (Klingman, 1970).
Weeds infest grazing lands across many climatic conditions ranging from arid to humid, on soils
varying from sand to clay, and in vegetative types from improved pastures to resident vegetation.
The selective control of weeds must be adapted to the situation and site where weeds are normally a
problem. Advantage can be taken of agronomic practices favorable to the vigorous growth of grasses
and legumes in pastures. The competition of vigorous forage species contributes to and helps hold
any gains made by the control method. The control method may need only to "tip the balance" in
favor of forage crops.
The only purpose and the primary impact of weed control is to change the vegetative composi-
tion of a site. Thus weed control always has an ecological impact. The objective is to change vegeta-
tive composition to a stage desired by man, which often is a subclimax vegetational type. The in-
direct effects of weed control are very important. Most of these are beneficial in some situations to
wildlife, domestic animals, birds, and man. It is also true that many indirect effects under some
conditions may be disadvantageous to one or more species. The direct harmful effect is usually
minimal. There is almost no correlation between the direct phytotoxicity of herbicides and animal
toxicity when all modern organic herbicides are considered.
Brush Control on Rangelands.—Brush removal can improve grazing on an estimated 240 mil-
lion acres (Armour's Analysis, 1952). Examples of important brush problems include 70 million
acres of mesquite (Prosopis spp.) (Parker and Martin, 1952), 76 million acres of juniper (Juniperus
spp.) (Anon., 1951), and 96 million acres of sagebrush (Artemisia spp.) (Pechanec et al., 1965).
More than 80 percent of grazing land in Texas alone is infested to some extent with brush (Smith
and Rechenthin, 1964).
Spreading of Native Plants to Become Weeds.—Originally, native woody plants were a lesser
component of the climax vegetation of North American grazing lands. Some authorities believe that
in early times repeated fires kept grasslands relatively free of woody plants (Humphrey, 1958). Dur-
ing those times, less intensive grazing of forage permitted enough grass to accumulate to serve as
fuel for the intense fires that killed young trees and shrubs. After settlement of the frontier, inten-
sive grazing steadily reduced the available fuel.
More recently, man has largely excluded fire from rangelands. The deterioration of ranges has
resulted in accelerated invasion by undesirable brush. For example, mesquite dominated only 5
percent of a southern New Mexico range before 1858, but had taken over 50 percent of the range
by 1963; tarbush occupied less than 1 percent of that area in 1858 and 9 percent in 1963 (Buffing-
ton and Herbel, 1965). Today, the brush invasion of grazing lands annually exceeds the acreage on
which control measures are applied (Day et al., 1968).
Management Practices That Should Accompany Brush Control.—Sound management principles
are essential to the use of control methods on brush-infested rangeland. Relatively little improve-
ment can be made, however, without eliminating the brush by spraying, burning, grubbing, root-
plowing, cabling, or some other method. Each method has specific advantages and many have cer-
tain limitations. Once established, woody plants like mesquite, juniper, oak, and sagebrush cannot
be eliminated by good grazing practices alone. Measures must be taken to convert the brush to more
productive types of vegetation. Brush control must be combined with other practices favorable to
forage production that will alter the direction of successional trends (Day et al., 1968).
Domestic livestock, game, rodents, and other animals contribute to range weed problems by
creating opportunities for the establishment of weed seedlings and spreading seed or vegetative
propagules. Grazing alters the botanical composition of range vegetation because of differences
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among species in palatability and ability to withstand grazing. The range animal, for example, first
grazes the most palatable forage plants on the more accessible parts of the range. As plants are pro-
gressively weakened by close and frequent cropping, the less palatable plants (weeds) grow unhin-
dered. Severe grazing can kill forage plants. Persistent heavy grazing increases the proportion of
short grasses at the expense of more productive taller grasses. Vigorous tall grasses offer resistance
to invasion by range weeds (e.g., mesquite) whose seedlings require intense sunlight. Good grazing
management usually results in more desirable species composition, vigorous individual forage plants,
and ample seed production. Usually, perennial grasses on arid rangelands thrive under stocking rates
that remove about 50 percent of the current year's herbage. Range seeding and related cultural prac-
tices can also be used to directly increase the density of the forage stand (Day et ai, 1968).
Seedings often fail to become established under the adverse environmental conditions of arid
and semiarid rangelands. Brush control is therefore of the utmost importance when invasion is just
beginning and before the grass has been depleted. Brush-infested lands that still have a good stand of
grass as understory require a herbicidal or mechanical brush-control method that does not destroy
existing grasses. Conversely, mechanical methods alone may be most effective if there is a dense
stand of brush with few or no desirable grasses, if the soil and climate are adequate to support grass
production, and if there is good probability of grass establishment after brush removal (Klingman,
1970).
Some measure of weed control may be obtained by selection of the kind of animals and the
timing of livestock grazing on a range. Goats, for example, browse on woody plants more heavily
than do cattle or horses. Sheep sometimes graze and thus control herbaceous weeds. However, live-
stock may also spread weeds from one range to another. The fruits of many range weeds are relished
by livestock, and their seeds are spread to uninfested areas when they pass through the digestive
tract in a viable condition. For example, in the case of livestock feeding on mesquite beans
(Prosopis spp.) or cactus fruits (Opuntia spp.), it takes a bout a week for the digestive tract to clear;
allowance should be made for this before moving the cattle to an uninfested range.
Some form of deferred or rotational grazing may be necessary to restore vigorous forage stands
on overgrazed sites near livestock water and salt. Appropriate intervals between grazing periods
allow the forage plants to regain vigor and set seed. Heavier stocking for only a part of the year
spreads grazing of forage plants on the more accessible sites. Adequate distribution of watering facil-
ities, judicious placement of salt, and other methods of spreading the grazing pressure over the en-
tire range reduce the danger of injury to forage plants and thus forestall weed and brush invasion
(Klingman, 1970).
The control of brush may require modification of currently practiced management systems.
Forage production for the first 2 to 4 years following successful brush control may be as much as
400 percent greater than before. This high production usually declines somewhat in subsequent
years. For example, the actual long-time improvement in forage production after brush control may
be only 30 percent on sandsage and mesquite rangelands and about 100 percent on shinnery oak
(Quercus harvardii) rangelands. Nevertheless, profits per acre on sandsage rangelands may be dou-
bled over a 20-year period by one successful brush-control operation. The increase in profits is even
higher when shinnery oak is controlled (Mcllvain, 1966).
In special situations, control of only a portion of the brush by herbicide treatments, rather
than the eradication or control of a high percentage, provides better long-time management alterna-
tives. Partial control of shinnery oak brush increases forage production from 50 to 100 percent and
usually gives a more manageable grass stand. On the light sandy soil habitat characteristic of shin-
nery oak the remaining oak plants also retard wind erosion during severe droughts. If only a part of
the area is treated, one should avoid concentration of livestock on the controlled acreage to the
point of causing overuse. Grazing of the controlled area should be deferred for a growing season or
more following treatment to allow the reestablishment of forage plants.
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In addition to increased grass production, brush control also results in the following:
1. Increased ease and reduced cost of caring for livestock
2. Increased number of offspring
3. Reduced screw worm and other parasite damage
4. Tamer livestock
5. Fewer breeding males required
6. Improved habitat for many species of wildlife
7. More groundwater production over a longer period of time (Klingman, 1970)
Methods of Brush Control
Methods used for brush control vary greatly in cost and effectiveness. Because the potential
income from grazing lands with a brush problem is low, costs and benefits of the alternative meth-
ods should be considered more carefully than may be necessary for more valuable lands. Because of
the large areas involved, brush eradication on rangeland is rarely the objective; emphasis is usually
placed on control or regulation of a problem species. A major difficulty in achieving control is the
efficient reproduction of many woody species. The capacity to regenerate asexually is common to
such problem species as mesquite, oak, elm, and cactus (Klingman, 1970).
Herbicidal Control
Foliage Sprays.—Herbicides such as 2,4-D, 2,4,5-T, Silvex, and benzoic acids control many
species of brush. Picloram also shows exceptional promise on many brush species. A combination of
2,4-D and 2,4,5-T is sometimes used to control mixed brush because of the varying susceptibility of
species, but 2,4-D and 2,4,5-T do not act synergistically, and their effects are not fully additive.
The choice of a herbicide is determined by cost, effectiveness, and safety. The relative costs of
herbicides are quite different. The least expensive is 2,4-D, and it is used where it is effective. The
cost of 2,4,5-T is about 2.5 times that of 2,4-D, and the former is used only when 2,4-D is inade-
quate. Similarily, dicamba is about six times as expensive as 2,4-D and picloram about 18 times.
Where possible and efficient, mixtures of more expensive herbicides with less expensive ones are the
rule. The expensive ones are used only when required for effective control.
Brush plants are most susceptible to foliage applications of herbicides after leaves have reached
full size, the flush of new leaf development has stopped, terminal growth has slowed, and before a
thick leaf cuticle is produced. This also coincides with the time that transport of photosynthate to
the roots peaks and when carbohydrate reserves stored in the root system and stem bases are at the
minimum level (Tschirley and Hull, 1959).
Plants are generally most sensitive to foliage sprays of growth-regulator herbicides under opti-
mum growing conditions. In some dry years herbicide treatments should not be made at all, since
plants under moisture stress do not readily translocate phenoxy herbicides. In Oregon, for example,
poor control resulted when the soil moisture was depleted before rabbitbrush reached a susceptible
stage of growth (Hyder et a/., 1962). Studies in New Mexico showed that there was a 39-percent
increase in the control of mesquite for each additional inch of rainfall during the October-to-May
period preceding treatment.
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Heavy applications of Silvex proved effective in controlling pricklypear (Opuntia polyacantha)
in Wyoming, particularly when spraying was preceded by running over the weeds with a cultipacker
(Thatcher et al., 1964). The cultipacker causes abrasions that apparently facilitate absorption. The
roller may also orient the pads in a horizontal position, which improves coverage.
Brush control on range lands does not last indefinitely after treatment. Many species resprout
trom the base of the stem or roots after the tops are killed by herbicides. The rate of recovery of
the brush cover, by sprouting, depends on species and environment. Treated areas also become re-
infested by seedlings arising from seeds present in the soil or brought in from nearby areas (Fisher et
al., 1959). In any event, re-treatment is necessary on sites where woody plants are well adapted. It is
important that the ranch managers plan for a long-range followup control program on their grazing
units.
To achieve adequate initial control of many woody plants, two or more herbicidal treatments
are necessary in consecutive or alternate years (Elwell et al., 1954). Adequate control usually lasts 7
to 15 years. Re-treatment of more susc'eptible brush species or species with weak regenerative
potential may be required at less frequent intervals.
The amounts of herbicide needed to give adequate control varies among species. Effective rates
are 0.33 to 0.5 Ib/acre of 2,4,5-T for velvet or honey mesquite; 2 Ib/acre of 2,4-D for big sagebrush
(Artemisia tridentata); and 2 Ib/acre of 2,4,5-T applied for 2 or more years for post and blackjack
oak (Quercus stellata and Q. marilandica). Higher rates are rarely more effective and may cause
foliage and branches to die so quickly that the herbicides are not translocated to the vital sites
(Klingman, 1970).
Fixed-wing or helicopter aircraft are commonly used to spray herbicides over large areas.
Foliage sprays can also be applied with ground equipment, but the terrain as well as the size and
density of the brush often preclude this.
Since minimal volumes and rates of herbicide are used in spraying for brush control, efficient
spray distribution is critical. Poor results can often be traced to poor spray distribution and cover-
age. The factors influencing distribution include swath width, height of spray release, nozzle place-
ment and orientation, and physical characteristics of the spray. In applying phenoxy herbicides to
mesquite, it has been established that about 70 drops per square inch are needed for minimum
coverage (Behrens, 1957). Finely atomized spray drops may drift from the target area or evaporate
before reaching foliage. Spray-droplet size should therefore be large enough to minimize drift haz-
ards but sufficiently uniform to provide good foliage coverage.
Soil Applications.— Variability in seasonal susceptibility is less of a problem with herbicides
absorbed from the soil than it is with foliage-applied herbicides. However, the rates or treatment are
often higher, and selectivity may be lower than that obtained with foliage sprays. Monuron,
fenuron, picloram, and other herbicides are applied as granules in broadcast treatments or around
the base of individual plants. Applications should be made when there is a reasonable chance that
rainfall will carry the herbicide into the soil. If herbicides are applied when rainfall is light, losses
through photodecomposition and volatilization may be excessive.
Individual stem treatments of brush with herbicides are usually limited to sparse stands of
single-stem trees or to small areas of range land. The three categories of stem or basal treatment are
basal stem, frill or tree injection, and cut stump.
In basal-stem treatments either diesel oil or kerosene, alone or fortified with a herbicide, is
sprayed on the base of the tree stem so that it thoroughly wets the bark and runs down the stem to
wet the crown at ground level. This method is particularly effective on hardwood trees, during
winter or summer, where the trunk diameter is less than 6 inches and the bark is not too thick.
Applications of phenoxy herbicides in a water carrier are not effective.
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Most species can be controlled with frill and tree-injection techniques. In the frill method
diluted or undiluted herbicides are introduced into cuts made around a tree stem with an ax or
some other sharpened tool. Horizontal cuts through the bark should be made as close to the ground
as possible. Tools for tree injection have a hole in a chisel point through which herbicide is injected
after the chisel is driven into the stem. Depending on plant size and species susceptibility, injections
must be made at intervals of from 1 to 3 inches around the stem. Treatments are effective during
any season.
The cut-stump method consists of treating the cut surfaces of a recently cut stump.
Ammonium sulfamate crystals, herbicides in diesel oil, or water-soluble herbicides in water are
applied to the cut surface. The method is effective with most sprouting species. Applying the herbi-
cide to the stump soon after cutting improves the likelihood of absorption before sprouting can
occur. Control is most effective if trees are cut close to the ground since the distance the herbicide
must travel to the sprouting zone is reduced.
Mechanical and Manual Methods.—The choice between manual methods (e.g., cutting and
grubbing) or mechanical equipment to remove brush depends on the size of the woody plants,
whether the species have sprouting or nonsprouting characteristics, soil condition, and type of ter-
rain. Mechanical methods have been used to control mixed stands of brush and species that occur in
almost pure stands. Various techniques and types of equipment have been developed for different
situations.
Manual Methods.—It is best to use manual methods of cutting or grubbing during early brush
invasion and before the grass stand becomes greatly reduced. Grubbing or cutting sparse stands of
small shrubs (up to 36 inches canopy diameter) by hand is an economical method of control
(Herbel et al., 1958). To kill a sprouting species, the root must be severed below the budding zone.
With large trees and multiple-stemmed plants the cost is usually prohibitive. After cutting, sprouting
species can be advantageously treated with herbicides to prevent sprouting.
Mechanical Methods—The mechanical methods of rangeland brush control include cabling or
chaining, bulldozing, rootplowing, disking.
Cabling or chaining is a process of uprooting trees by pulling a 300- to 500-foot length of
anchor chain or heavy cable looped between two large tractors traveling in the same direction. This
method is most effective in controlling even-aged, mature, nonsprouting species such as one-seed
and Utah juniper. It is less successful against sprouting species such as mesquite and against stands
of brush that include both small and mature plants (Klingman, 1970).
Small shrubs or trees are not severely damaged by this method. Medium-sized trees or shrubs
may be only partially uprooted. Stands containing a large number of small- or medium-sized trees
require followup work by bulldozing or by hand. The method is not effective if the terrain is too
steep or has gullies and exposed rocks. Tractors should maintain the highest possible speed.
Cabling or chaining is most successful on areas with a light soil and fairly level topography
supporting plants of 3 inches or more in diameter. Small plants bend under the chain or cable and
snap back without appreciable damage.
Bulldozing is effective against medium-sized trees of some basal sprouting species and sparse
stands of any species since it pushes or pulls the plants out of the soil. Small trees and shrubs are
often overlooked and may not be removed by this method. Large trees are difficult to uproot. One
problem with bulldozing is that much soil is torn up, leaving large pits.
Bulldozer blades may be fitted with a projection, sometimes called a stinger, which is pushed
under the tree crown to ensure uprooting of the bud zone. Experienced operators can lift and push
over a tree in one smooth operation. Another equipment modification is a blade that can be both
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tilted and angled. Experienced operators can cause far less soil disturbance with this type of blade
than with a normal bulldozer blade. Bulldozing is difficult on steep, rocky land.
In Arizona the cost of bulldozing an acre with 100 predominantly small juniper trees was $6,
and the cost for the same number of larger trees was $9. Cost per tree decreases as density increases
because of the shorter travel time between trees. In a hardwood-pine area bulldozing costs were $11
per acre for a tree density of 427 per acre if 90 percent of the trees were 6 inches or less in diameter
at breast height. Costs may exceed $20 per acre for larger trees. Followup treatment is required
because small plants are missed and resprouts and seedlings soon appear.
Rootplowing with a track-type tractor and a horizontal blade cuts off brush below the ground
surface. Rootplowing is limited to deep soils that are relatively free from rocks and obstructions.
Fins are welded to the top of the back of the blade to push roots out of the ground and reduce the
possibility of their rerooting. Rootplowing generally kills most of the brush that the blade strikes
below the budding zone of plants and also kills almost all the grass in the area.
Because areas that are rootplowed must be seeded, the operation should be conducted only in
areas favorable to the establishment of the forage seeding. Rootplowing and seeding are expensive
operations. The cost-to-benefit ratio is generally favorable when a good grass stand is established
and unfavorable when seeding is unsuccessful (Boykin, 1960). Because of the high percentage of
control obtained, rootplowing is effective where there is no seed source of the woody plants either
in the soil or in nearby areas. It is often difficult to establish new seedings on arid and semiarid
range lands where brush is a problem.
Disking for brush control is done with a large disk plow, or tandem disk, which plows up much
of the brush. The method is limited to small, shallow-rooted plants such as creosotebush, sagebrush,
and tarbush. Soils must be plowable and should contain few desirable grasses since disking destroys
most of the grass present. Disked areas must be seeded with desirable grasses. Limitations are gen-
erally the same for disking as for rootplowing (Klingman, 1970).
Burning is the oldest brush-control method in use. Prescribed burning may be one of the most
useful but more hazardous brush-control practices. The results of burning vary greatly depending on
the susceptibility of the species to fire and on the amount of fuel accumulation from the associated
forage species. The time of year and moisture relationships are also important. Because of these
variations and the hazards to other resources, the value of burning as a brush-control measure is
controversial (Lillie et al, 1964; Jones and Laude, 1960).
If burning is employed, consideration, must be given to the direct effects of fire on forage spe-
cies and the tendency for livestock and other animals to concentrate in recently burned areas.
Forage species vary in their susceptibility to fire, and the season of greatest susceptibility for the
undesirable plants may or may not coincide with that of the forage species. Heavy grazing, coupled
with frequent burning, will eliminate the better forage plants.
Burning at the proper season—with proper moisture conditions, appropriate grazing manage-
ment, and adequate precautions—effectively controls several kinds of undesirable range shrubs. Big
sagebrush is an example of a species that does not sprout strongly after burning (Pechanec et al.,
1965; Blaisdell, 1953). Fire gives a very limited degree of control, however, of a number of shrubs
and trees—such as velvet mesquite (Prosopis juliflora var. velutina) (Cable, 1961), the oaks (Martin
and Crosby, 1955), several species of the chaparral complex, and alligator juniper—since they re-
sprout vigorously at or near the ground. Under certain conditions, however, as in the case of young
velvet mesquite plants in southern Arizona and chaparral in California, burning may still be useful as
a method of control. After burning, seeding is commonly done in the ashes. Sprouts and seedling
brush and weeds should be sprayed the year after burning. The spraying of older brush is less effec-
tive.
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Burning is no cure-all for the range-brush problem, nor is it necessarily cheaper than other
methods. Provision must be made to ensure that the fires do not get out of control. This requires
adequate preparation, trained manpower, fire-control equipment, prearranged fire breaks, and judg-
ment as to when burning should be undertaken and when and where it can be stopped. The use of
desiccating herbicides to permit more latitude in selecting the time and place of burning is under
investigation but is not a widely recommended practice. The cost of burning includes not only the
cost of fire lines and other safety precautions but also the loss of one or more forage crops that are
necessarily accumulated as fuel to carry the fire. However, burning does offer a degree of control
for a number of species wherever it can be properly integrated into a comprehensive, long-range
vegetation-management program.
In areas where smoke pollution is a serious problem the use of fire for brush control would
likely be considered unacceptable by the public. Furthermore, burning bares the soil, which in turn
increases the hazard of wind and water erosion and the consequent pollution of streams and the air
with soil particles.
Biological Control and Selective Grazing Methods.—Since the inception of biological control of
lantana in Hawaii in 1902, steady progress has been made. Striking successes have been obtained in
Australia with prickly pear, in California with St. Johnswort, in Fiji with curse, and in Hawaii with
pamakani (Day et al., 1968).
Successes in biological weed control suggest that perennials in noncultivated environments are
better adapted to biological control than are short-lived species in cultivated situations.
Because the ultimate geographic distribution of an introduced biotic agent is not usually con-
trollable, all conflicting interests concerning the weed itself should be resolved before an introduc-
tion is made. Conflicts of interest arise because some weed species in one situation may be consid-
ered to be valuable plants in others (Day et al., 1968).
Biological control of weeds is highly useful and promising on certain individual species. Never-
theless, this method can be used effectively on only a small percentage of economically important
weeds, if only because of the conflicts of interest that exist. The other weed species must be con-
trolled by other methods.
Selective grazing by sheep or goats is effective in controlling some species of brush in small
areas. The animals select the more palatable plants or portions of the plants and are particularly
effective in controlling seedlings and young sprouts. Therefore cutting or otherwise removing the
tops of larger trees and shrubs precedes this practice. Close, continuous grazing is necessary to sup-
press and kill brush. Overgrazing, especially at the wrong times of the year, can be more detrimental
to desirable forage species than to the brush species being controlled (Johnston and Peake, 1960).
Expenses for the necessary fences, water, death losses, and management of animals 'can prove ex-
orbitant.
Methods of Herbaceous Weed Control
Herbaceous weeds are found in all rangelands. Their harmful effects vary with the range condi-
tions: good ranges usually have few herbaceous weeds, and poor ranges have many. Loss of forage
from herbaceous weeds on rangelands is often less spectacularly apparent than from dense stands of
brush; nevertheless, such losses are large.
Grasses are a most important group of herbaceous weeds, and they dominate vast areas of
rangelands throughout the world. For example, medusahead (Taeniatherum asperum) is spreading in
California, Oregon, Washington, Idaho, and Nevada. It is invading stands of forage plants as well as
the downy brome (Bromus tectorum) and other weed species found on millions of acres of range
lands. Except for a short time in the spring, this weed is unpalatable. Because of its low palatability,
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it accumulates and thus creates a fire hazard. Dead litter also tends to build up and inhibit the early
growth of seedlings of planted species.
Downy brome differs from medusahead in that it serves as the main forage species on millions
of acres of western range. It is productive and palatable in the spring. However, this annual is unde-
sirable on many ranges in that well-adapted perennial grasses (or other perennial plants) give a more
reliable and higher production of forage, especially in adverse years. As downy brome matures, its
palatability decreases, and its usefulness as forage declines (Klingman, 1970). Furthermore, the dead
plants are a serious fire hazard.
The control of downy brome and medusahead often requires the seeding of perennial grasses
combined with grazing-management practices that favor the desirable forage species. Otherwise, any
management will yield little except downy brome and medusahead. After the initial establishment
of perennial grass seedlings, selective herbicide treatments should be applied to suppress the weeds
and thus enhance the rapid development of the perennial grass plants to a level of vigor and basal
density that maintains suppression of the weedy annual grasses (Torrell et al., 1961).
That at least partial control of two successive crops of medusahead is required for a successful
seeding operation illustrates an important principle related to annual weed control. Regardless of
the number of plants per unit area—be it 10 or 1000—their control is essentially a matter of percent-
ages, and high populations are best reduced by successive control measures (Torrell, 1966). For
example, in southwestern Idaho medusahead populations range from 250 to over 1000 plants per
square foot, with mean values of 325 to 400 plants per square foot. Initially, there may have been
as many as 14,000 seeds per square foot. A controlled fire before seed shattering will destroy much
seed and reduce the next year's medusahead population 85 to 90 percent below that of unburned
areas. Therefore there will be about 35 plants per square foot on the burned site and about 350 on a
similar area on the unburned site. Dalapon applied at a rate of 2 Ib/acre will kill 98 percent of both
populations in the spring a year after burning. The surviving population on the burned site will be
some 0.7 plant per square foot versus about seven plants on the unburned site. Practically, this may
represent the difference between the success and failure of a new seeding of perennial grass.
Under climatic conditions like those found in parts of California and Nevada, 1 year of tillage
in April will give weed control adequate for the establishment of legumes or forage grasses, espe-
cially if seeding is accompanied by other weed-control treatments and if annual forage species are
seeded (Kay and McKell, 1963).
Control procedures in new seedings would be greatly simplified if there were a truly selective
herbicide that would kill the annual weed species and leave the seeded species uninjured. The simi-
larity in physiological and environmental requirements of seedlings of annual and perennial grasses
makes such selective control of weed grasses one of the most persistently difficult problems in range
improvement. The potentialities for such a herbicide are best illustrated by siduron, which selec-
tively controls the seedlings of crabgrass (Digitaria spp.), foxtail (Setaria spp.), downy brome,
medusahead, and many others without injuring the seedlings of bluegrass (Poa spp.), crested wheat-
grass (Agropyron desertorum), and fescue (Festuca spp.). For siduron to be effective, moisture must
be available soon after treatment. This limits the usefulness of this herbicide for range seedings.
Several of the wheatgrasses (Agropyron spp.) are suitable for seeding in ranges infested with
downy brome and medusahead. Mature plants of the wheatgrasses are strongly competitive, but not
the seedlings. The use of selective herbicides releases wheatgrass plants from the intense competition
of weed grasses.
Paraquat has proved effective in weed-control experiments in Nevada and northeastern Cali-
fornia in a program of no-tillage spring seeding of perennial grasses. Paraquat plus a surfactant effec-
tively controls downy brome seedlings and is almost immediately adsorbed by the soil and plant
residues; this permits the seeding of perennial grasses immediately after spraying. When added to
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paraquat, 2,4-D controls the broadleaf weeds that are often associated with downy brome. Paraquat
must be applied in the spring, when moisture is often available for only a short time, leaving a short
period for seeding operations. Stands of perennial grasses must be established early so that these
forage plants are large enough by summer to stand the drought and heat. In years of extreme
drought, the chances of successful seeding are almost nil despite the degree of weed control that is
obtained. Planting the seed in furrows improves the microenvironment and enhances the probability
of perennial grass establishment.
Herbicides active in the soil, such as atrazine, effectively control annual grasses but are toxic to
the seedlings of perennial grasses. To achieve selectivity between the weed and the seeded species, it
is necessary to use methods that are based on timing, placement, or a combination of both. A chem-
ical fallow technique in which atrazine is applied in the fall of one year and perennial grasses seeded
the next has been effective over 10 years of experimentation (Eckert and Evans, 1967). Atrazine is
nearly always dissipated from the soil in the intervening year. Weed control during that year elimi-
nates seed production and conserves nitrogen and soil moisture. This technique reduces annual
grasses markedly during the seeding year but sometimes increases broadleaf weeds. Under such con-
ditions, good stands of crested and intermediate wheatgrasses have been obtained by planting the
seed in furrows in the fall and spraying broadleaf weeds with 2,4-D the following spring.
Broadleaf Herbaceous Weeds.—Broadleaf herbaceous weeds are serious problems in rangelands
since many are unpalatable or have spines or thorns. Because livestock avoid such weeds, unless
other forage is lacking, broadleaf weeds tend to increase on improperly grazed ranges. Furthermore,
they compete directly with desirable forage species for moisture and nutrients, decrease the amount
of forage produced, and inhibit the establishment of forage seedlings (Day et al., 1968).
The control of broadleaf herbaceous weeds is complicated by the fact that individual species
often occur in scattered stands and frequently on terrain that is not easily accessible for direct con-
trol measures. Some species, such as the low larkspurs (Delphinium spp.), mule-ears (Wyethia spp.),
and lupines (Lupinus spp.), occur in stands of sufficient density and area to justify overall applica-
tions of herbicides.
Many species, notably the larkspurs and deathcamas (Zigadenus spp.), become more resistant
to phenoxy herbicides at later growth stages. The time of treatment is therefore critical. In addition,
plants of such species as the tall larkspurs begin growth as snowbanks recede. This results in many
growth stages among closely associated plants of the same species. Under these conditions, plants
may range from susceptible to resistant, and therefore re-treatment will be necessary and adequate
control costly.
The extensive root systems of some perennial herbaceous weeds, as exemplified by Canada
thistle (Cirsium arvense), leafy spurge (Euphorbia esula), hoary cress (Cardaria draba), and whorled
milkweed (Asclepias verticillata), and the variable effectiveness of phenoxy herbicides on such
plants make repeated treatments necessary. Despite the need for repeated annual treatments,
phenoxy herbicides are used alone and in combination with improved grazing management, cultiva-
tion, and reseeding. Reasonable control can be achieved in this way, but near eradication from a site
requires prolonged treatment. In a 6-year study in the Gulf Coast area of Texas, the application of
2,4-D (1 Ib/acre) in March of each year resulted in an average increase in forage production from
2400 to 5300 Ib/acre. The annual cost for the operation was $2 per acre (Hoffman and Ragsdale,
1964).
Poisonous Weeds.—About half the perennial broadleaf herbaceous range plants presently recog-
nized as weeds are poisonous. Examples of locally abundant poisonous species in climax vegetation
are tall larkspur, greasewood, chokecherry, and certain oaks. Many poisonous plants increase in
density on misused rangelands because they are not grazed when palatable forage plants are availa-
ble. There are exceptions, however, such as tall larkspurs (Delphinium spp.) and locoweeds (Astraga-
lus spp.), which may be habit-forming to livestock (Day et al., 1968).
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Poisonous plants are found on nearly all rangelands in the Western United States. Whether they
present a problem on range depends on a number of factors. The toxicity of poisonous plants varies
with the species and with its stage of growth. Sneezeweeds (Helinium spp.) are mildly poisonous;
animals may become ill but seldom die if removed from the infested area when symptoms appear.
Timber milkvetch (Astragalus miser) is so toxic that once cattle exhibit symptoms, they seldom
recover; it is, however, apparently relished by cattle and sheep. Tall larkspurs are most toxic during
early growth stages. Halogeton (Halogeton glomeratus) becomes more toxic with age. Jimsonweed
(Datura spp.) is very unpalatable and seldom eaten unless animals are starving.
Sparse infestations of poisonous plants are seldom troublesome. Heavy stands of even mildly
toxic plants constitute a hazard to livestock. Even small areas of dense infestations of highly toxic
species may remove large areas of grazing land from profitable production.
Proper grazing management permits avoidance of poisoning by some species. The life cycle of a
poisonous plant can determine whether and when it is a problem on a range. Low larkspurs and
deathcamas are problems on ranges grazed very early in the year because they are among the earliest
green plants available to livestock. On similar ranges that are grazed later in the season, when forage
plants are larger, the animals seldom eat the poisonous species. Still later in the season both poison-
ous plants have completed their life cycles and disappeared from the range. Tall larkspurs, however,
may be at their maximum toxicity during the grazing season.
Poisonous plants are not equally poisonous to all classes of livestock. Tall larkspurs and timber
milkvetch are far more toxic to cattle than to sheep. Conversely, only a few cattle losses are def-
initely known to be due to halogeton, whereas thousands of sheep losses can be attributed to the
plant.
Poisoning by weeds causes heavy losses of animals and is a most persistent problem of the
range livestock producer. Estimates based on a large number of reports indicate about 3 to 5 per-
cent deaths on tall larkspur-infested range lands. Deaths in some years exceed 15 percent.
Where good range management or other biological control methods do not reduce poisonous
weed populations to nonhazardous levels, herbicide treatments may be necessary. Properly timed
applications of specific phenoxy herbicides control many poisonous weeds. Repeated annual treat-
ments are required for many perennial species and for annuals and biennials if there is a residual
seed supply. The benzoic acids and picloram show special promise against some poisonous weeds.
On sites where herbicides are used for control, judicious grazing management is essential to
increase desirable vegetation both in vigor and number of plants, thus reducing the possibility of
reinfestation. If an area does not contain sufficient palatable species for natural revegetation, it
should be seeded. Proper herbicide treatments after seeding will reduce weed competition and in-
crease the probability of successful seeding and control even on marginal sites. This fact has been
demonstrated many times in salt-shrub desert vegetation when halogeton or Russian thistle were
controlled in a seeding of crested wheatgrass (Haas et al., 1962).
Brush and Weed Control on Pastures
Every pound of herbaceous weeds grown in pastures reduces the production of desirable forage
plants by about an equal amount. Reduction in forage attributable to weeds varies and depends on
moisture conditions and the weed and pasture species involved. If legumes are established in the
space occupied by weeds, the production of forage will be proportionately greater because of the
legume's vigorous growth habit and ability to fix nitrogen (Klingman and McCarty, 1958).
Principles of Pasture Management.—Any practice fostering the development of a thick sod and
vigorous growth of permanent pasture species will in time reduce the density of many weed species.
Grasses and legumes in pastures vary widely in vigor and density. The vegetation on most permanent
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pastures of the humid region consists of volunteer grasses and weeds. The forage-weed balance is
extremely variable, and in areas with naturally nonacid soils, common white clover (Trifolium
repens) will usually volunteer.
Liming and fertilization are particularly effective in reducing the weed component over a
period of time. In Connecticut, applications of nitrogen, phosphorus, and potassium on a sparse
stand of Colonial bentgrass (Agrostis tennis) resulted in a shift to denser bluegrass sod and a conse-
quent reduction in weed growth. Some weed species, however, are favored by fertilization. Exam-
ples are chickweed (Stellaria media) and curly dock (Rumex crispus), which are severe problems
only on fertile soils.
Weed-control measures in pastures should foster a high production of nutritious and palatable
forage. Weeds can now be controlled by herbicides alone and in combination with other manage-
ment procedures in pastures more effectively and more efficiently than ever before. In pasture-
forage production, all beneficial practices must be integrated into the management system to
achieve highest efficiency.
Brush- and Weed-Control Methods.—The general principles and techniques used to control
brush and weeds on rangelands also apply to pastures. In general, pastures are more intensively man-
aged and have a higher production capacity. There is, therefore, more flexibility in the choice of
possible methods of control on pastures than on rangelands. The potential for a greater increase in
forage production may permit the choice of more expensive methods. Moreover, fertilization and
liming are more important in weed and brush control on pastures than on arid rangelands.
A large part of the land pastured in the United States is cut-over forest land. Here, without
constant control of sprouts and seedlings, the land will gradually revert to timber and shrub species.
The major woody plants that must be kept under control include oak (Quercus spp.), hickory
(Garya spp.), cedar (Juniperus spp.), pine (Pinus spp.), poplar (Populus spp.), maple (Acer spp.),
sweetgum (Liquidambar spp.), holly (Ilex spp.), basswood (Tilia spp.), persimmon (Diospyros spp.),
sassafras (Sassafras spp.), buckbrush (Symphoricarpos spp.), rose (Rosa spp.), elder (Sambucus
spp.), hazel (Harnamelis spp.), elm (Ulmus spp.), and blackberry (Rubus spp.).
The potential of phenoxy herbicides for controlling weeds in pastures, alone and in combina-
tion with other agronomic practices, has been demonstrated in studies conducted at several loca-
tions in the humid and semihumid areas of the United States. These herbicides, including 2,4-D,
2,4,5-T, (4-chloro-o-tolyloxy)acetic acid (MCPA), Silvex, and 4-(2,4-dichlorophenoxy)butyric acid
(2,4-DB), alone or in combinations, control a wide spectrum of broadleaf weeds and brush.
Picloram shows particular promise for killing some weed and brush species.
The practice of mowing many annual and biennial weeds in pastures during the bloom stage of
growth largely prevents seed production and may eventually eliminate the weed from the pasture
(Klingman and McCarty, 1958). The time of mowing is critically important. Prostrate species and
those that branch laterally from buds close to the ground cannot be controlled by mowing. Herbi-
cides are more effective on such species. Even then herbicide treatments may be required for several
years to exhaust the supply of weed seed in the upper soil stratum.
Plants growing under optimum conditions are usually more susceptible to herbicides than
those doing poorly in adverse environments. Moderately high soil moisture and relative humidity
with an air temperature in the range of 70° to 80° F appear to be the optimum conditions for
phenoxy herbicides to be effective.
Perennial weeds vary greatly in susceptibility to phenoxy compounds, not only between spe-
cies but between ecotypes within a species. Variable responses to 2,4-D, ranging from resistance to
susceptibility, have been found among ecotypes of Canada thistle (Cirszum arvense) in Montana
(Hodgson, 1964). In Oklahoma perennial ragweed (Ambrosia psilostachya) has been readily con-
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trolled by 2,4-D at rates as low as 1 Ib/acre. Applications of 1 and 2 Ib/acre controlled this weed in
central Nebraska; but at Lincoln, Nebraska, a stand of perennial ragweed plants was not reduced on
pasture plots sprayed annually for 20 years with an ester of 2,4-D at 1 Ib/acre (McCarty et al.,
1974).
A few perennial species can be controlled by a single herbicide treatment, but usually one or
more re-treatments are required. Re-treatments not only improve the control of perennial weeds but
remove crops of annual weeds as well. Herbicide use should continue through the years until the
weed stand is reduced adequately. Herbicide treatments, combined with proper fertilization and
grazing management, should result in the replacement of weeds by forage species (Peters and
Stritzke, 1971).
In many pastures a wide spectrum of broadleaf weeds may create control problems. Rotation
of kinds of herbicides or repeated treatments within the season may therefore be needed to carry
out an effective control program where a mixture of winter-annual, annual, biennial, and perennial
weeds exists. For example, treatments may be necessary in early spring for thistle rosettes, many
species of the mustard group, dandelions, and the common snowberry. Such treatments may pre-
cede the susceptible stage of emergence of such weeds as iron weed (Veronia baldwini), hoary ver-
vain (Verbena stricta), goldenrod (Solidago spp.), aster (Aster spp.), and ragweed.
The use of 2,4-D and other phenoxy herbicides may retard the growth of such legumes as
white clover and lespedeza (Lespedeza spp.). Stands of legumes may be depleted by early spring
spraying. Ordinarily, white clover and lespedeza will recover and eventually benefit from the elimi-
nation of weeds and the improved management practices accompanying weed control. If white
clover is an important component of the pasture vegetation, 2,4-DB should be used since it causes
little injury to white or ladino clover and controls many weeds susceptible to 2,4-D.
Combinations of spraying and mowing have been inadequately explored in pasture weed con-
trol. In some areas mowing is desirable for reasons other than weed control. It may, for example,
encourage more uniform grazing and favor development of the associated legumes.
Selected Data Comparing Different Methods of Weed and Brush Control
In comparing alternative methods of controlling weeds and brush, it should be recognized that
the effects resulting from different methods of control are never exactly the same. Therefore in a
strict sense the comparisons are not valid. If one method kills all the weed species but one and a
second method kills all but one other weed species, the results from control in an area will seldom
be the same because of the different characteristics of the species that escaped treatment.
The coincident impacts of different methods on soil, air, water, flora, and fauna are also quite
different. The relationships of the impacts on these environmental factors will vary with site. For
example, denuding the land by mechanical treatment or burning will be more likely to result in
water erosion on steep, erosive soils than on nearly level, stable soils. Selective control by herbicides
usually leaves the vegetation in place. Because of the herbicides' selectivity and slowness of action,
the species of plants that are not killed increase in size and cover coincident with the slow death of
unwanted species, thus providing soil protection.
Each weed situation, site characteristic, and geographic location will also influence the choice
of control method. The chances of successfully reseeding after rootplowing are reduced in very arid
climates and on steep slopes. Burning on grazing land near metropolitan areas may be unacceptable
because of the smoke that pollutes the air. Use of phenoxy herbicides near cotton fields or residen-
tial areas may be prohibited, especially when cotton is growing. In many states these herbicides can
be used only before cotton is planted and after it is harvested.
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Table 1. FORAGE PRODUCTION UNDER SEVERAL COMBINATIONS OF SPRAYING,
TILLAGE, AND SEEDING ON BIG SAGEBRUSH RANGE, 1950-19531
_ 2 Forage yield, oven-dry
Treatment^ ' . . Cost of treatment
(Ib/acre)
Plowed and drilled 921 $9.00
Sprayed, disked, and drilled 842 11.35
Sprayed, not seeded 508 3.35
No treatment 137 0
'Source: Cornelius and Talbot (1955).
'Sprayed with 2,4-D in July 1948; seeding done in fall of 1948.
Table 2. YIELD OF OVEN-DRY FORAGE ON TREATED AND UNTREATED SILVER
SAGEBRUSH RANGE, 1951 AND 19531
T 2 Forage yield, 2-year average Estimated
(Ib/acre) cost of treatment
None 60 0
Sprayed with 2,4-D 459 $3.35
Sprayed with 2,4-D and drilled 790 $8.35
Plowed and drilled 882 $9.00
1 Source: Cornelius and Talbot (1955).
2 Sprayed with 2,4-D in 1948; seeding done in fall of 1948.
Selected examples comparing the results of different weed-control methods illustrate some of
the differences among the methods and reasons why different methods may be chosen under vari-
ous situations. Much of this information is presented in tables to facilitate comparison.
Eight years of research in the plateau region of northeastern California have shown that seed-
ing and weed control are practical means of quickly restoring productivity and reducing erosion on
deteriorated rangelands (see Tables 1 and 2).
Research in California has also shown that ranges with terrain too steep, erodable, or rocky for
cultivation can be successfully seeded by spraying the resident annual grasses with paraquat and
planting immediately (see Table 3).
The spring following seeding, hording grass plants in the unsprayed plots were mere threads
with two or three leaves and 2 to 7 inches high. In plots sprayed with paraquat the plants were
robust, had one to six leafy tillers, and were 12 inches high. The plants in unsprayed areas died dur-
ing the summer, while those in the sprayed plots survived to produce large, mature plants the sec-
ond year.
Removal of fringed sage in North Dakota by spraying 2,4-D at a rate of 2.5 Ib/acre significantly
increased yields from all treatments (Lorenz and Rogler, 1962). During a 12-year, eight-treatment
crested wheatgrass renovation study, the average yields for sprayed and unsprayed plots were 1461
and 1137 Ib/acre, respectively. The average increase in yield for spraying in the 3 years was 57 per-
cent.
In Colorado 13 prominent weed species decreased 40 percent or more after the application of
2,4-D at a rate of 2.2 kg/ha (Hyder, 1971). This resulted in a botanical composition that was grazed
more uniformly and completely. Hence, spraying mixed-grass prairie with 2,4-D improved the range
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Table 3. PERCENT HARDING GRASS AND SUBCLOVER ESTABLISHMENT
ON PLOTS SPRAYED AND SEEDED OCTOBER 25, 1963, IN
SONOMA COUNTY1
Treatment
Check (no spray)
Paraquat treatment:
Complete coverage
1 1-inch band
5.5-inch band
LSD, 0.05 level
Subclover,
April 1964
48
81
80
74
14
Harding grass,
January 1965
0
75
60
58
17
'Source: Kay (1966).
condition and increased forage production. Yields of oven-dry forage, averaged for the 3 years, were
580, 710, and 680 kg/ha for untreated plots and for plots sprayed before and after the heading of
sandberg bluegrass, respectively. "There are no known alternative ways of making these improve-
ments in a reasonable time" (Hyder, 1971).
"Natural rehabilitation of mule-ear-infested ranges by protection from grazing requires many
years and is believed beyond the realm of economic practicality" (Tingey and Cook, 1954). Mule-
ear was successfully controlled in Utah with 2,4-D applied at a rate of 2 Ib/acre. In one case, 5 years
after treatments were made, a series of untreated plots infested with mule-ear yielded 280 Ib/acre of
desirable forage; where the weed had been eliminated, the yield was 1353 Ib/acre. Bunch wheat-
grass, Kentucky bluegrass, and needle-and-thread grass increased in direct proportion to the extent
of mule-ear control.
Five years after spraying oak-hickory vegetation with 2,4,5-T in Missouri, the total herbage
yield was about 4.5 times that on the burned areas and 5.5 times that on the control area (Ehren-
reich and Crosby, 1960).
Demonstrations in all parts of Texas have shown that it is nearly impossible to eradicate brush
from grazing land. Brush-infested range lands can be restored to high production when the land-
owner plans and carries out a complete brush- and weed-control program, including maintenance
control and improved grazing management (Hoffman, 1970).
From 1965 to 1969 there was mechanical weed and brush control on 2.8 million acres of graz-
ing land in Texas, and chemicals were used on 2.9 million acres. During the last 10 years the acreage
under mechanical control remained about the same, and the acreage under chemical control more
than doubled (Hoffman, 1970).
Information from the Rio Grande Plain region of Texas and in the post and blackjack oak re-
gion of Texas shows that all brush-control methods are economically feasible, with the exception of
bulldozing. Bulldozing is not usually used in this area for range improvement except in particular
situations (Morrow et ai, 1962).
Chemical methods increased net returns for the benefit life of the treatment by $23.62 per
acre in the post oak region and by $4.47 per acre in the mixed-brush areas of south Texas. Many
brush species of the Rio Grande Plain (south Texas) are not well controlled by 2,4,5-T. Rootplow-
ing and reseeding increased the net return by $35.35 per acre, and chaining increased it by $6.03
per acre (Morrow et al., 1962).
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Research in Nebraska has shown mowing to be relatively ineffective on many perennial weeds
in pastures but moderately effective in controlling several annual and biennial species (see Table 4).
Good control of most troublesome broadleaf weeds results from successive annual applications of
2,4-D at a rate of 1 Ib/acre. The total forage consumption increased as the proportion of broadleaf
weeds in the material consumed decreased.
Some cost estimates show the difference in return for different practices in a weedy pasture
(see Table 5). The advantage of spraying 2,4-D over mowing for weed control in this pasture is obvi-
ous. The use of 2,4-D resulted in gains intermediate between the check and improved pastures that
were plowed and reseeded. The cash outlay for spraying was relatively low.
Spraying with 2,4-D reduced lanceleaf ragweed populations more than did mowing (Peters and
Stritzke, 1971). Four annual sprayings with 2,4-D reduced stands of yarrow by 66 percent; mowing
had little effect. Spraying 2,4-D for 3 years nearly eliminated ironweed; mowing for 4 years reduced
ironweed by about 50 percent.
High-level fertility plus 2,4-D increased by 1000 Ib/acre the consumption of forage by cattle
over the high-fertility, no-weed-control treatment; high fertility plus mowing increased consumption
by about 200 Ib/acre (Peters and Stritzke, 1971). Plowing, fertilizing, and seeding orchardgrass and
ladino clover eliminated weeds for 2 years, but in the third year the orchardgrass stand became thin
and weeds became numerous. One year's production was lost because the first seeding failed to be-
come established. When all years of the experiment were considered (including the years of no pro-
Table 4. SIX-YEAR AVERAGE OF DRY-MATTER CONSUMPTION UNDER
DIFFERENT WEED-CONTROL METHODS IN A DEFERRED AND
ROTATIONALLY GRAZED PASTURE NEAR LINCOLN, NEBRASKA1
_ Forage consumed
Treatment ,,, , . Percentage of weeds
(Ib/acre)
None 880 41
Mowed2 1100 19
Sprayed (2,4-D)2 1250 7
Plowed, seeded, and sprayed 2500 4
'Source: McCarty and Scifres (1968).
2 Data from mowed and sprayed plots represent averages of June and July treatment dates. Sprayed
plots annually received 1 Ib/acre of 2,4-D, isopropyl ester, on the same dates as mowing.
Table 5. ESTIMATED AVERAGE ANNUAL COSTS AND RETURNS PER ACRE FROM VARIOUS
SYSTEMS OF PASTURE MANAGEMENT IN NEBRASKA1
Estimated pounds of Value of beef at Average Net return
beef per acre $0.20 per pound annual cost per acre
Rundown native pasture:
Check 76 $15.20 $7.50 $7.70
Mowed 56 11.20 8.20 3.00
Sprayed (2,4-D) 95 19.00 8.70 10.30
Improved pasture:
Brome grass
WSG mixture
148
163
23.68
26.08
7.50
9.20
16.18
16.88
'Source: Finleyefa/. (1958); estimates projected over a 10-year period.
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duction on orchardgrass), the amounts of forage consumed were about equal on the orchardgrass
plots and on those receiving high fertility plus 2,4-D.
Picloram killed nearly all the goldenrod plants in a timothy crop (Peters and Lowance, 1969).
The 2,4-D and 2,4-DB formulations reduced yields of goldenrod by 75 to 95 percent. Timothy was
not noticeably injured by the herbicides, and its yields increased by 0.8 to 1.0 pound for each
pound of weeds that failed to grow. There is no other known way of selectively controlling these
weeds in this grass crop.
"Increased streamflow has been noted for 3 successive years since a streamside strip within
central Arizona watershed was chemically treated to convert chaparral to grass cover. Prior to treat-
ment, the channel was dry several months each year. Since treatment, flow has been continuous at
the outlet, and water has been permanently available for wildlife and livestock at several places
along the channel" (Anon., 1970, p. 31).
"Winter grazing studies with tame mule deer on sagebrush ranges in central Colorado revealed
that deer prefer forbs and grasses over sagebrush. These studies . . . also suggest that careful use of
2,4-D herbicide with fertilizer can improve the vegetative composition of these important areas for
deer grazing" (Anon., 1970, p. 16).
As a result of several seasons' use of 2,4-D and 2,4,5-T in southern Michigan, it is generally
agreed that use of the herbicides has enabled biologists to do a better job of habitat management
than was done in the past (Ruch, 1957). There is an urgent need for economical methods of creat-
ing and maintaining openings by controlling unwanted vegetation. Such openings are important to
grouse, rabbits, and deer.
Restricting the use of phenoxy herbicides on 62 million acres of all cropland would eventually
substantially increase cost to consumers (Fox et al., 1970). The immediate effect would be an in-
crease of $290,000,000 in production costs to farmers. In addition, farmers and their families
would have to work 20 million more hours to control the weeds without these herbicides. The
farmers would receive no additional income for this extra labor.
REFERENCES
Anonymous, 1951. Report on Control of Undesirable Plants on Rangelands, Forest Service, U.S.
Department of Agriculture, Range Reseeding Committee (mimeographed).
Anonymous, 1952. Armour's Analysis, 1(4), 3.
Anonymous, 1970. Forestry Research Highlights, Rocky Mountain Forest and Range Experimental
Station, Forest Service, U.S. Department of Agriculture, p. 31.
Anonymous, 1970. Forestry Research Highlights, Rocky Mountain Forest and Range Experimental
Station, Forest Service, U.S. Department of Agriculture, p. 16.
Behrens, R., 1957. Weeds, 5, 183.
Blaisdell, J. B., 1953. Ecological Effects of Planned Burning of Sagebrush-Grass Range on the Upper
Snake River Plains, U.S. Department of Agriculture Technical Bulletin 1075.
Boykin, C. C., Jr., 1960. Costs of Root Plowing and Seeding Rangeland, Rio Grande Plain, Texas
Agricultural Experimental Station Miscellaneous Publication 425.
Buffington, L. C., and Herbel, C. H., 1965. Ecol. Monog., 35, 139.
Cable, D. R., 1961. J. Range Mgmt., 14, 160.
Cornelius, D. R., and Talbot, M. W., 1955. Rangeland Improvement through Seeding and Weed
Control on East Slope of Sierra Nevada and on Southern Cascade Mountains, U.S. Department
of Agriculture Agricultural Handbook No. 88.
Day, B. E., Barrens, K. C., Fertig, S. N., Freed, V. H., Hamm, P. C., Huffaker, C. B., Klingman, D.
L., Staniforth, D. W., and Upchurch, R. P., 1968. Principles of Plant and Animal Pest Control,
110
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Vol. 2, Weed Control. National Academy of Sciences, Washington, B.C., pp. 86-119 and
267-294.
Eckert, R. E., Jr., and Evans, R. A., 1967. J. Range Mgmt., 20, 35.
Ehrenreich, J. H., and Crosby, J. S., 1960. J. Range Mgmt, 13, 68.
Elwell, H. M., Elder, W. C., Klingman, D. L., and Larson, R. E., 1954. Proc. llth Annual Meeting,
North-Central Weed Control Conf., pp. 91-95.
Evans, R. A., Eckert, R. E., Jr., and Kay, B. L., 1964. Proc. 7th Brit. Weed Control Conf., pp. 767-
770.
Finley, R., Brown, D., Baker, M., Guyer, P., and Hanway, D. G., 1958. Does It Pay to Improve
Your Pasture? Nebraska Agricultural Extension Service, CC169.
Fisher, C. E., Meadors, C. H., Jr., Behrens, R., Robinson, E. D., Marion, P. T., and Morton, H. L.,
1959. Control of Mesquite on Grazing Lands, Texas Agricultural Experimental Station Bulletin
935.
Fox, A. S., Jenkins, R. P., Andrilenas, P. A., Holstun, J. T., Jr., and Klingman, D. L., 1970.
Restricting the Use ofPhenoxy Herbicides, U.S. Department of Agriculture Economic Report
No. 194.
Haas, R. H., Morton, H. L., and Torrell, P. J., 1962. J. Range Mgmt., 15, 205.
Herbel, C. H., Ares, F. N., and Bridges, J. O., 1958. J. Range Mgmt., 11, 267.
Hodgson, J. M., 1964. Weeds, 12, 167.
Hoffman, G. O., and Ragsdale, B. J., 1964. Range Weed Control, Texas Agricultural Extension
Service Miscellaneous Publication 746.
Hoffman, G. O., 1970. Texas Brush and Weed Control Acreages. RM3-1 (mimeographed).
Humphrey, R. R., 1958. Bot. Rev., 24, 193.
Hyder, D. W., Sneva, F. A., and Freed, V. H., 1962. Weeds, 10, 288.
Hyder, D. N., 1971. Weed ScL, 19, 526.
Johnston, A., and Peake, R. W., 1960. J. Range Mgmt., 13. 192.
Jones, M. B., and Laude, H. M., 1960. J. Range Mgmt., 13, 210.
Kay, B. L., and McKell, C. M., 1963. Weeds, 11, 260.
Kay, B. L., 1966. Calif. Agr., 20(10), 2.
Klingman, D. L., and McCarty, M. K., 1958. Interrelations of Methods of Weed Control and Pasture
Management at Lincoln, Nebraska, 1949-55, U.S. Department of Agriculture Technical
Bulletin No. 1180.
Klingman, D. L., 1970. In FAO International Conference on Weed Control, Weed Science Society
of America, pp. 401-424.
LeClerg, E. L., 1965. Losses in Agriculture, U.S. Department of Agriculture Agricultural Handbook
No. 291.
Lillie, D. T., Glendening, G. E., and Pase, C. P., 1964. J. Range Mgmt., 17, 69.
Lorenz, R. J., and Rogler, G. A., 1962. J. Range Mgmt., 15, 215.
Martin, S. C., and Crosby, J. S., 1955. Burning and Grazing on Glade Range in Missouri, U.S. Forest
Service, Central States Forest Experimental Station Technical Paper 147.
McCarty, M. K., and Scifres, C. J., 1968. Farm, Ranch and Home Quart., University of Nebraska
(Winter).
McCarty, M. K., Klingman, D. L., and Morrow, L. A., 1974. Interrelations of Weed-Control and
Pasture-Management Methods at Lincoln, Nebr., 1949-69. In preparation.
Mcllvain, E. H., 1966. Personal communication.
Morrow, J., True, C. W., Jr., and Harris, V. M., 1962. An Economic Analysis of Current Brush
Control Practices, Southwest Agricultural Institute and The M. G. and Johnnye D. Perry
Foundation, Bulletin No. U2.
Parker, K. W., and Martin, S. C., 1952. The Mesquite Problem on Southern Arizona Ranges. U.S.
Department of Agriculture Circular 908.
Pechanec, J. F., Plummer, A. P., Robertson, J. H., and Hull, A. C., Jr., 1965. Sagebrush Control on
Rangelands, U.S. Department of Agriculture Agricultural Handbook No. 277.
Peevy, F. A., 1962. Weeds, 10,14.
Peters, E. J., and Lowance, S. A., 1969. Weed Sci., 17, 473.
Ill
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Peters, E. J., and Stritzke, J. F., 1971. Effects of Weed Control and Fertilization on Botanical Com-
position and Forage Yields of Kentucky Bluegrass Pasture, U.S. Department of Agriculture
Technical Bulletin No. 1430.
Ruch, L. C., 1957. Down to Earth, Spring, p. 2.
Sampson, A. W., and Schultz, A. M., 1957. Control of Brush and Undesirable Trees, Vol. 10, No. 1,
FAO, Rome, Italy.
Smith, H. N., and Rechenthin, C. A., 1964. Grassland restoration: The Texas brush problem. SCS,
USD A, Temple, Texas.
Thatcher, A. P., Davis, G. V., and Alley, H. P., 1964. J. Range Mgmt., 17, 190.
Tingey, D. C., and Cook, C. W., 1954. Farm and Home Sci., Utah State Agr. Expt. Sta., pp. 5, 16,
17.
Torrell, P. J., Erickson, L. C., and Haas, R. H., 1961. Weeds, 9, 124.
Torrell, P. J., 1966. Personal communication.
Tschirley, F. H., and Hull, H. M., 1959. Weeds, 7, 427.
U.S. Department of Agriculture, 1968. Extent and Cost of Weed Control with Herbicides and an
Evaluation of Important Weeds, 1965. Publication ARS 34-102.
U.S. Department of Agriculture, 1972. Extent and Cost of Weed Control with Herbicides and an
Evaluation of Important Weeds, 1968, ARS-H-1.
AQUATIC USES
Some form of aquatic vegetation occurs in all streams and bodies of water. It is as essential to
the aquatic environment as other plants are to the terrestrial environment. The ecological signifi-
cance of aquatic vegetation exceeds that of any other forms of aquatic organisms. It provides the
basis of the food chain for other forms of aquatic life and is the habitat for much of the aquatic
fauna. Essential as they are, excessively large populations or masses of aquatic plants may become
highly detrimental to other aquatic organisms and reduce the usefulness of water for many other
purposes.
Characteristics and Distribution of Troublesome Aquatic Vegetation
Aquatic vegetation is readily observed in all but the coldest, deepest, or most heavily polluted
waters. Even in these waters, close examination usually reveals some type of plant life. The forms
of aquatic vegetation range from microscopic plankton to large vascular plants such as cattail
(Typha spp.) and waterhyacinth [Eichornia crassipes (Mart.) Solms]. Under certain environmental
conditions and water quality criteria, all forms can create problems in water.
Algae.—Algae are nonvascular plants that range in size from microscopic unicells to macro-
scopic filaments, sheets, clusters, or tubes. In a few genera, such as Chara, the algae may appear to
be rooted vascular plants. Algae are almost universally present in water. Many species are quite
specific as to the ecological sites they may occupy. Some species prefer hard or alkaline waters,
others prefer soft water of low pH. A characteristic common to many algae is their appearance in
"blooms" during certain periods. A bloom may consist of a single species or may be due to several
species. In some waters the succession of blooms during a given season can be predicted with rea-
sonable accuracy. In irrigation systems it is more typical to observe a single predominant species
(usually filamentous) during the entire season.
Vascular Aquatic Plants.—This group consists of a vast array of floating, submersed, emersed,
and marginal weeds. Many are useful and desirable species that provide food and habitat for water-
fowl, fish, and aquatic insects; some are desirable for their aesthetic value. Certain species are
largely undesirable and add little to the total aquatic environment.
Floating Plants.—These plants float individually or in mats on the water surface. They vary in
size from the minute duckweed (Lemma minor L.) to the large species, such as waterhyacinth and
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alligatorweed [Alternanthera philoxeroides (Mart.) Griseb]. The more troublesome floating plants
are of tropical or subtropical origin and are of most concern in the Southern states.
Submersed Plants.—These are rooted plants that grow submersed in water, although they may
frequently grow to the water surface. This group includes such species as American pondweed, which
have flat leaves that float on the water surface. Typical of submersed plants are the pondweeds
(Potamogeton spp.), elodea (Elodea canadensis Michx.), and watermilfoil (Myriophyllum spp.).
Emersed Plants.—Emersed plants are rooted in the soil and rise above the water surface. Be-
cause they are usually restricted to shallow water, they are commonly found in most drainage canals
and ditches and on the shorelines of streams and lakes. Cattails, bulrush (Scirpus spp.), and picker-
elweed (Pontederia spp.) are common emersed species.
Marginal Plants.—Marginal aquatic plants commonly occur at the margins of lakes and streams.
Many of these plant species are also adapted to wet marshy sites. Some of the most important of
these weeds are grasses, including johnsongrass [Sorghum halepense (L.) Pers.], reed canarygrass
(Phalaris arundinaceae L.), and paspalum (Paspalum spp.). Other common marginal weeds are sedge
(Carex spp.), smartweed (Polygonum spp.), and primrose (Jussiaea spp.).
Activities and Resources Affected by Aquatic Vegetation
There is scarcely an activity or resource involving water that is not affected in some way by
aquatic vegetation. The biological productivity of water can be maintained only by the presence of
aquatic flora. Ideally, the mass of vegetation produced should be adequate to support the various
other forms of aquatic life at the optimum level without preventing or limiting the other beneficial
uses of water. In many situations, the strata of productivity of aquatic plant life that support
specific activities at optimum levels will be in conflict with other uses. A satisfactory solution
would be to maintain the vegetative productivity at the highest level tolerated by all or the majority
of the various activities and resources affected.
irrigated Agriculture.—Irrigated agriculture is totally dependent on an adequate supply of
water during the growing season. The consequences of any lengthy interruption in delivery of water
during this period are disastrous to the farmer who depends on irrigation water. The planning of
irrigation districts is such that, when fully developed, water-conveyance structures must operate at
full capacity to satisfy the needs of all farmers in the district. Unfortunately, irrigation canals pro-
vide ideal sites for the growth of certain algae and vascular weeds, which soon invade these areas.
Even small amounts of algae and rooted weeds cause significant losses in the volume of water flow.
Heavy infestations can reduce water flow as much as 80 to 90 percent and cause water levels to rise
and wash out canal banks. Not only is valuable water lost but flooding occurs in the vicinity of the
break while other farmers must do without water until repairs are made. Algae and other aquatic
plants also lodge in water outlets, siphons, pumps, sprinklers, trash racks, and other structures,
causing lost time, inefficient use of water, and large maintenance expenses..
According to statistics from the agricultural census (USDA, 1959, 1964), there are more than
2 million farm ponds and reservoirs (many used for irrigation), 189,000 miles of drainage ditches,
and 173,000 miles of irrigation canals in the United States. A survey of weed problems on irriga-
tion systems in 17 Western states (Timmons, 1960) reported that 63 percent of the 144,000 miles
of irrigation canals were infested with aquatic weeds. Also, more than 75 percent of 530,000 acres
of canal banks were infested with a variety of weeds. Similar weed problems occur in other areas of
the country. In 1965 direct losses to agriculture in the United States caused by aquatic and bank
weeds amounted to $52,000,000 (USAGE, 1965). The net productive value of lost water alone was
estimated at $91,000,000 (USDA, 1965).
Recreation.—The extent to which aquatic vegetation influences or affects recreation has never
been determined; whether such a determination is possible is questionable. Most of the streams and
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natural and artificial water impoundments are multiple-purpose resources. Some of the recreational
uses are not compatible. Swimming, waterskiing, and pleasure boating are not entirely suited to
waters managed primarily for fishing or waterfowl production. Many observations and experience
support contentions that aquatic vegetation is a serious problem affecting recreational uses of
water. While aquatic plants are a natural and essential component of the aquatic environment, they
can despoil this environment simply by their presence in excessive numbers and in areas where they
are undesirable.
Property Values.—There are few recorded or reported instances of property values being
affected by aquatic vegetation. Nevertheless, the history of property development adjacent to lakes
and streams is ample evidence that aquatic weeds are an important element in determining the value
and desirability of such property. Clear weedfree or relatively weedfree lakes and streams have
always had a high priority for the location of waterfront homes and vacation facilities. Serious in-
festation by aquatic weeds subsequent to the development of such areas drastically reduces the
desirability and value of waterfront property. Holm et al. (1969) cite an example of the effect of
aquatic vegetation on the operation and value of a resort motel and marina constructed on what was
once one of Florida's finest streams. Eighteen months after opening, this recreational facility,
constructed at a cost of almost $1,000,000, was closed and forced into bankruptcy because of the
sudden invasion by the submersed weed hydrilla (Hydrilla verticillata Casp).
Property values may also be affected by the presence of mosquitoes and other insects, snakes,
vermin, dead fish, foul odors, and other conditions associated with excessive growths of aquatic
vegetation. Other examples of depreciations in value and damage of property are (1) clogging of
navigable streams; (2) washing out of bridges, boat docks, and other structures; (3) flooding and
altering of water courses; (4) damage and loss of boats, motors, and other fishing equipment.
Wildlife Management.—Because many species of aquatic plants provide valuable food or habitat
for certain mammals, reptiles, amphibians, and birds, the manipulation and control of weed species
is basic to wildlife management. Each form of wildlife has specific habitat requirements, and often
certain aquatic plants may adversely affect habitat quality. Conversely, some undesirable species of
wildlife are attracted to certain vegetation types and must be controlled. Even more important are
the preservation and maintenance of habitats of rare or endangered species.
Replacement of solid stands of waterhyacinth or other aquatic weeds with more desirable forms
of vegetation achieves the diversity of species required for wildlife habitat affording open areas for
resting, food production and foraging, protective cover, and rearing of adult or young aquatic
animals and, in particular, migratory waterfowl (Walker, 1969). Public use of wildlife areas requires
maintenance of access routes, boat landings, water movement channels, and canals and protection
from flooding, safety hazards, noxious insects, and vectors of diseases.
The beneficiaries of these wildlife management programs are the 14,386,000 hunters who
spend more than $2,000,000,000 annually, or about $149.46 per hunter, and 85,819,000 recrea-
tion days (Anon., 1972). Waterfowl hunters alone averaged $84.47 per hunter and 25,113,000
recreation days. In addition, recreation was provided for 6,813,000 bird watchers, 4,519,000 wild-
life photographers, and 26,906,000 nature walkers who spent 411,371,000, 37,828,000, and
337,092,000 recreation days, respectively, in these activities. These activities are critically depend-
ent on aquatic areas and are among the primary concerns of wildlife refuge management.
Fisheries Management.—Environmental quality dictates the existence of acceptable fisheries,
and control of plant life is the fundamental basis for fisheries management. Uncontrolled growth of
vascular plants and algae can divert solar energy and nutrients from food-chain organisms or other
desirable plant life (Walker, 1971). Excessive plant density adversely affects predator-prey relation-
ships, can result in fish kills, block fish migration, inhibit distribution, or engender spawning fail-
ures, mortalities of fry-fingerlings, and undesirable changes in water chemistry (Walker, 1964a).
Recreational and commercial fisheries are especially affected by high pH, poisonous gases, toxins,
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low dissolved-oxygen concentrations, various kinds of pestilence, pathogens, and fish food orga-
nisms associated with weed growths. Herbicides and algicides promote the stabilization of ecologi-
cal conditions and are essential in integrated systems of fishery management involving dynamic
biological, chemical, and physical environmental factors. Stagnation and degradation of water
quality, nutrient availability, and radiant energy often determine the value of fishery habitats, the
occurrence of desirable species of fish, and the quality and economic values of recreation and fish
products (Walker, 1972).
More than 706 million recreation-days and about $5,000,000,000 ($150 per fisherman) are
spent annually by approximately 28 million fishermen (Anon., 1972). By the year 2000 it is ex-
pected that the present 82 million acres of inland fishing water will increase to 92 million (Anon.,
1962), primarily in the form of warm-water reservoirs, which are subject to the greatest weed prob-
lems (Walker, 1969 and 1971). The projected requirement at that time is 680 million fisherman-
days for 63 million fishermen (Walker, 1972; Condon, 1968). Thus even more intensive fishery
management (and use of pest control chemicals) will be required.
Potable Water Supplies.—Algae, especially the blue-green species, commonly cause undesirable
flavors in potable water supplies. Water-treatment processes do not remove these flavors, and the
only available recourse is heavy chlorination. Vascular aquatic plants also contribute to the poor
quality of potable water. The decay of large masses of dead plants creates pollution conditions
similar to those of sewage and industrial wastes. It has been estimated that the oxygen-depleting
pollution load of 1 acre of growing waterhyacinth is equivalent to the sewage produced by 40
people (U.S. Congress, 1957). The pollution loads are vastly greater, but of shorter duration, with
species that mature and die during short periods within, or at the end of, the growing season.
Navigation.—Interruptions of, and inconvenience to, navigation, except on a limited scale,
occur primarily in waters of the Southern and Southeastern United States. The inland waterways of
the coastal regions form an extensive network that is vital to the transport of materials to and from
the areas. Considerable economic loss occurs when this traffic is delayed or stopped by accumula-
tions of aquatic vegetation. In addition to interference with both commercial and pleasure naviga-
tion, there is costly damage to boats and bridges. Drifting mats of waterhyacinth, when piled up
against bridge supports, can move and shift the entire structure. Logs and other obstructions con-
cealed by the plants provide additional hazards to navigation. It is estimated that without adequate
control of aquatic plants, navigation (and considerable land traffic) would almost cease in these
waterways within a 2-year period.
Aquatic Vegetation Management With Herbicides
The management of aquatic weeds is accomplished largely with herbicides at present. Informa-
tion concerning the total area of aquatic weed infestations and the extent of herbicide use is not
available or is fragmentary at best. Twenty states reported the use of herbicides on weed infesta-
tions totaling 216,000 acres in 1968 (USDA, 1972). This was almost 2.6 times the area reported
treated by 13 states in 1965. The average cost of treatment was $20.50 per acre. These figures are
not indicative of the magnitude of the problems, nor do they provide a measure of the total area in
which herbicide use would be beneficial.
Algae
Copper Sulfate.—Copper sulfate is widely used to control algae in amost all situations requiring
chemical control. The present tolerance for copper sulfate in potable water is approximately 4
ppmw of the crystalline pentahydrate form. This level of treatment is rarely if ever used purposely
for algae control. Copper sulfate is toxic to fish, particularly trout, and except in hard water should
not be used at rates above 1 ppmw (DeVaney, 1968). It is inadvisable to use copper sulfate in trout
waters except when the need for algae removal exceeds the value of the fish that may be killed
(Walker, 1969). Rates for the control of blue-green algae range from 0.5 to 1 ppmw; for filamen-
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tous algae from 1 to 2 ppmw; and if used as a "slug" treatment in flowing water, 0.3 to 2 pounds
per cubic foot of water flow per second. Copper sulfate does not injure crops or other land plants,
although it may injure vascular aquatic plants that are used as ornamental plantings. Used at recom-
mended rates, it presents no known hazard to higher animals. Copper sulfate may have an adverse
effect on aquatic microfauna, especially where used frequently, continuously, or at heavy rates,
particularly in softer waters (Walker, 1969).
Cutrine, a mixture of copper sulfate and triethanolamine, is used to some extent for algae con-
trol. It appears to be more effective in hard, or alkaline, waters, where copper sulfate alone does
not always give good results. Triethanolamine is reported to prevent or delay the loss of copper
sulfate due to the formation of insoluble precipitates. Fish appear to tolerate higher rates of copper
in the presence of the amine additive.
Dichlone.—This compound is effective primarily on blue-green algae. Though it is reported to
have a very low acute toxicity to warm-blooded animals, it is very toxic to fish (Walker, 1969). It
may not be used in potable water. There is very little advantage in the use of dichlone over copper
sulfate except in industrial water where the presence of copper is objectionable.
Dichlobenil.—The macroscopic alga Chara is especially susceptible to dichlobenil. Because of
the cost, it is rarely used for the control of Chara alone, although situations do arise where Chara by
itself is a major problem. The application rates recommended for dichlobenil have been designed
primarily for vascular plants; consequently, the minimum effective dosages for the control of Chara
alone are not defined (DeVaney, 1968).*
Other Herbicides.—Other herbicides that will eliminate all or certain species of algae are acro-
lein, aromatic solvent, diquat, and endothall (Walker, 1969). These are broad-spectrum herbicides
and are usually used to control one or more species of vascular weeds. The control of algae is for
the most part incidental to this use. These herbicides are covered in detail in other sections.
Floating Weeds.—Floating weeds are particularly troublesome in the Southern states. The
most serious problem species, such as waterhyacinth, alligatorweed, waterlettuce (Pistia stratiotes
L.), and waterferns (Azolla spp., Saluinia rotundifolia Willd.), are for the most part from the tropics
or subtropics. They do not die back during the winter, although their rates of growth decrease.
Hindrances to navigation arise primarily from the excessive growth of floating weeds. With the
possible exception of alligatorweed, they are more easily controlled than most submersed
vegetation.
2,4-D.—This herbicide can be used at rates of 1 to 4 Ib/acre to control most species of floating
aquatic weeds. Waterhyacinth is particularly susceptible to 2,4-D and is often treated at rates of 1
to 1.5 Ib/acre. Alligatorweed is the most resistant, and treatment rates may be increased to 6 to 8
Ib/acre. In addition to being an exceptionally effective herbicide, it is unfortunately hazardous to
use in some areas and during some seasons because of the danger that spray and vapors will drift to
sensitive crops and ornamental plants. In these instances, substitute herbicides are employed.
There are few proved hazards to animal life due to the direct toxicity of 2,4-D. Modifications
in the aquatic environment are due largely to the removal of the aquatic vegetation, and these are
generally of short duration. Although a few ester formulations are directly toxic to fish, the
greatest hazard to the aquatic environment is the alteration of water quality due to the death and
decay of large masses of vegetation after the use of 2,4-D (and other herbicides). The decay of
organic matter and the attendant low levels of oxygen result in the suffocation of fish and other
aquatic animal life. The subsequent anaerobic fermentation produces high levels of hydrogen sul-
fide and other metabolites toxic to both animal and plant life. These undesirable effects are experi-
*See page 119 for additional information on dichlobenil.
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enced only in impounded water or in sluggish moving streams, and they are known to occur fre-
quently from natural causes in waters having precariously balanced ecology states. Residues in
water, soil, and fish appear to be short-lived—less than 60 days in the Southeastern United States.
Silvex.— The preceding discussion of 2,4-D is equally applicable to Silvex. Although it may be
used widely to control floating vegetation, its principal use is as a substitute for 2,4-D in the control
of alligatorweed. Field tests have shown that Silvex will provide longer lasting control of this weed.
Residues in water, soil, and fish are also slightly more persistent.
Diquat.— Where circumstances make it undesirable or unsafe to use 2,4-D, diquat may be used
to control duckweed, waterhyacinth, and waterlettuce. Diquat is injected into the water or sprayed
over the surface to control duckweed. It may be sprayed over the water surface or applied by air to
control waterhyacinth and waterlettuce. In water containing sediment of any kind, diquat is
rapidly adsorbed and inactivated.
When used at recommended rates, diquat is nontoxic to wildlife (Condon, 1968; Heath et al.,
1972; Pimentel, 1971; Tucker and Crabtree, 1970), fish, and other aquatic animals (Walker, 1969;
Condon, 1968; Pimental, 1971; Battelle, 1971; Lawrence and Hollingsworth, 1969). Its persistence
in water is short and usually is reduced to traces in 3 to 4 days. However, a 10-day waiting period
after treatment is recommended before use of the water is resumed. The persistence of residues in
bottom soils and fish has not been fully investigated.
Submersed Weeds in Irrigation Canals and Ditches.—Aquatic vegetation in irrigation convey-
ance systems is difficult to control. The water is constantly flowing (usually at a fairly high veloc-
ity), which results in the transport of herbicide chemicals from the site of application. To provide
adequate contact time for lethal dosages to be absorbed by the vegetation, herbicides must be
applied to the water continuously for periods known to be effective. Consequently, large volumes
of water must be treated at considerable expense. In addition, herbicides must usually be applied to
water that will in a short time be diverted onto cropland. In irrigated areas water is scarce and not
to be wasted. During the time when weeds are most troublesome, the canals must operate continu-
ously at full capacity to deliver the volumes of water required to satisfy the needs of the farmers.
Thus it is impractical to interrupt the flow of water to cropland by shutting down the flow in the
canals or by denying diversion of water to crops. Water not diverted to cropland must be returned
to some water system in which herbicide residues might be hazardous.
Acrolein.— Acrolein is usually used as a contact herbicide in large irrigation canals where the use
of aromatic solvents is too costly. Application rates vary from about 0.1 to 0.6 ppmw. Treatment
times (contact periods) range from 8 to 48 hours. In general, the larger the canal, the lower the
treatment rate and the longer the contact period. Infrequently, smaller canals may be treated at
rates of up to 15 ppmw for 30 minutes to 4 hours. Irrigation canals and ditches with little grade and
very slow moving water may be treated in the same manner as impounded water by injecting 4 to 7
ppmw of acrolein beneath the water surface along the entire length of the canal.
Because acrolein is very toxic to fish (Condon, 1968; Walker, 1969; Battelle, 1971), its use
must be restricted to waterways where fish are of minor importance. In addition, treated water
should not be permitted to enter other waters until the acrolein has been dissipated. The effects of
acrolein on fish and other aquatic organisms have not been fully investigated.
Aromatic Solvent.—Aromatic solvents (almost exclusively xylene of not less than grade B) have
been used in irrgation canals with a flow of up to 100 ft3/sec for more than 25 years. Application
rates vary from 6 to 10 gallons per 1 ft3/sec of water flow applied over a period of 30 to 60
minutes. An emulsifier is added to the xylene (1 to 2 percent) before injection into the water.
Xylene is volatile and is lost quite rapidly, making booster applications necessary at intervals of 2.5
to 5 miles.
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Aromatic solvents, like acrolein, are contact herbicides and are effective on algae as well as
vascular aquatic weeds. They are very toxic to fish, crayfish, and other aquatic animals but have an
exceedingly good record of safety to crops and warm-blooded animals (Pimentel, 1971). It is com-
mon practice for farmers to continue diverting water onto crops during periods when xylene is used
for weed control. Because xylene is used primarily in the smaller canals of water distribution sys-
tems, there is usually very little waste or return water: all the water is diverted by the time it
reaches the end of the system. Because of its volatility and breakdown of the emulsion during the
irrigating process, practically no solvent remains in drainage water (usually very small volumes if
any) from irrigated fields. Livestock and other animals refuse to drink water containing more than
trace amounts of aromatic solvents.
Copper Sulfate.—The continuous-feed method of using copper sulfate to control submersed
aquatic plants has been used only rarely, and mainly on experimental bases. Field trials have shown
that 1 ppmw used early in the season, followed by about 0.5 ppmw later in the season when the
water is warmer, will control algae and some species of vascular aquatic plants. No acute toxicity to
fish has been observed. Chronic toxicity to fish and other aquatic fauna in irrigation systems has
not been determined.
Diquat.— The use of diquat in irrigation systems has been restricted to situations where there is
virtually no movement of the water. Diquat is ineffective in turbulent water and in water con-
taining appreciable quantities of suspended solids. It is very readily adsorbed to plant or mineral
matter, and water residues are usually present in only trace amounts 2 to 4 days after treatment.
Although it would probably be safe to use irrigation water 3 to 4 days after treatment with diquat,
present restrictions require a waiting period of 10 days. It is not toxic to fish when used at the
recommended rates of 0.25 to 1.0 ppmw. Effects on other aquatic organisms appear to be largely
indirect and caused by habitat modification.
Endothall.— Restrictions concerning the sites of use of the sodium and potassium salts of endo-
thall are the same as for diquat. Treatment rates vary from 1 to 5 ppmw, depending on the level of
weed infestation. The water should not be used for any purpose except swimming for 7, 14, or 25
days after treatment at rates of 1, 3, or 5 ppmw, respectively. Swimming is permitted after 24 hours.
Fish may be used for food 3 days after treatment with any endothall derivative. The effects of the
sodium salt of endothall on other components of the aquatic environment are largely the result of
habitat modification; effects of the alkylamine salts have not been thoroughly investigated.
The alkylamine salts of endothall are more phytotoxic than the inorganic salts, and they are
also much more toxic to fish (Walker, 1969). Rates above 0.3 ppmw may cause fish mortality
(Walker, 1964a). Both liquid and granular formulations are usually used at 0.5 to 2.5 ppmw—but
only for spot treatment or where fish kill is not objectionable. Use of the granular formulation re-
duces the hazard to fish. Waiting periods for water uses after treatment are 24 hours for swimming,
3 days for use of food fish, and for other uses 7, 14, and 25 days after applications of 0.3, 3, and 5
ppmw, respectively. The effects of the alkylamine salts of endothall on the aquatic environment
have not been investigated fully.
Monuron.— This herbicide cannot be used in the main channels of irrigation systems. Its princi-
pal use is to control vegetation in lateral ditches that carry water intermittently and directly to irri-
gated fields. Since herbicides used in these ditches are not linked directly to other water systems,
they are of only secondary importance.
Diuron.—The use of diuron is the same as for monuron.
Submersed Weeds in Drainage Ditches.—Many of the factors and conditions governing the uses
of herbicides in irrigation canals and ditches apply equally to drainage ditches. In some drainage
ditches fish may be of considerable importance, in others they may be nonexistent or of little im-
portance. Also, some drainage ditches may have sizable water flows, while others have essentially
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no flow during much of the year. Drainage ditches commonly empty into water impoundments or
streams. Water from drainage ditches is also used occasionally for irrigation. In treating drainage
ditches for control of vegetation, the precautions that must be observed depend on the circum-
stances of the specific situation.
Acrolein.—Drainage ditches with flowing water are treated in the same manner as irrigation
canals. The same precautions should be observed. Drains with little or no water flow should be
treated in the same manner as irrigation canals with little flow or with all flow checked (see p. 131).
Copper Sulfate.—May be used infrequently in drainage ditches where the vegetation is predomi-
nantly algae. Application rate may have to be increased if treatment is made after algae become
heavily matted or if the water is shallow, hard, or alkaline. If there is little or no flow, the entire
length of the ditch should be treated. See Clc for precautions and other information.
Other Herbicides.— Diquat, endothall, and aromatic solvent are also used in this application.
Lakes, Ponds, and Reservoirs.—Aquatic vegetation problems are most numerous in lakes,
ponds, and reservoirs. It is here that we can anticipate much greater demand for improvement in
the environment through the management of aquatic plants. The nation is experiencing wholesale
development of almost all available waterfront property. In many areas without natural bodies of
water they are being constructed as integral parts of residential developments. At the same time,
the recreational uses of water have increased greatly. For various reasons, the quality of water in
lakes, ponds, and reservoirs has deteriorated and continues to do so. Algae problems now exist in
waters where they were never observed previously. Vascular aquatic weeds frequently pollute and
reduce the usefulness of waters valued for generations as favored fishing and other recreational
sites. Awareness of the problems, and knowledge that methods are available that may alleviate
these even temporarily or in part, will undoubtedly result in pressures to improve the aquatic envi-
ronment through vegetation management. Permanent solutions, if there are any, must include
measures to prevent the pollution and enrichment of the water. In the foreseeable future, signifi-
cant improvements made in the aquatic environment through vegetation management will probably
involve the use of some herbicides.
Dichlobenil.—When used as a broadcast treatment on exposed bottoms or over the water sur-
face, the granular formulation of dichlobenil provides excellent control of vascular aquatic plants
and Chora. For best results the treatments should be made before or when weed growth begins.
Treatment rates recommended are 7 to 10 Ib/acre when applied to exposed lake- or pond-bottom
soil and 10 to 15 Ib/acre when applied through the water. The effects of dichlobenil on aquatic
vegetation are usually confined to the actual area treated.
Dichlobenil is not acutely toxic to fish except at application rates 30 to 60 times greater than
those recommended for weed control. Whole fish contain residues at levels that approximate those
present in the treated water. It is persistent in confined water, and residues have been observed for
periods of up to 4 months. For these reasons, dichlobenil cannot be used in potable, irrigation, or
livestock water. Fish are not to be used for food or feed for 90 days after treatment.
Diquat.— Application rates of diquat for control of submersed weeds range from 0.25 to 1.5
ppmw, depending on the susceptibility of weeds treated. These rates apply to treatments of entire
bodies of water. For spot treatments the rates are frequently doubled to ensure adequate control of
the weeds. Combining applications of copper sulfate and diquat are more effective on the more toler-
ant species of aquatic weeds than diquat alone but must be used with caution in fish habitats. Treat-
ments commonly consist of 1 ppmw each of copper sulfate and diquat. For precautions to be fol-
lowed and other information concerning the effects of using copper, see p. 129.
Endothan.—The various derivatives of endothall are broad-spectrum herbicides. The disodium
and potassium salts are active on most submersed species of aquatic plants (Lawrence and Hollings-
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worth, 1969; Walker, 1969). They are notably ineffective on Elodea. The inorganic salts are used at
rates of 1 to 5 ppmw. The higher rates (4 and 5 ppmw) are used for spot or marginal treatments.
Fish are not harmed at these rates and may be used for food 3 days after treatment. Because of the
short persistence of endothall in water, swimming is permitted after a 24-hour waiting period, and
other water uses may be resumed 7 days after treatment with 1 ppmw. The total effects of the
sodium salt of endothall are the result of habitat modification (Walker, 1964a and 1972; Condon,
1968). For alkylamine salts of endothall, refer to page 132.
Fenac.—Present uses of fenac are limited to situations in which water can be drawn down to
expose the bottom soil of ponds and lakes. Fenac is applied to the exposed soil at rates of 15 to 20
Ib/acre. The ponds and lakes should not be refilled sooner than 3 weeks after treatment. Fenac
does not appear to be hazardous to fish and other nontarget organisms. Gross observations of
treated waters to date suggest that its effects on the aquatic environment are minimal. However,
this herbicide is very persistent in water (for as long as 3 to 6 months), and residues in fish have not
been fully investigated.
2,4-D.—Various derivatives of 2,4-D are used to control submersed aquatic vegetation
(DeVaney, 1968). The most commonly used derivatives are esters, such as the butoxyethanol and
isooctyl esters. Less frequently used are the sodium salt of 2,4-D and the amine salts, such as the
dimethylamine salt. Because of the real or presumed higher levels of phytotoxicity, the esters have
most often been preferred. Granular or pelleted formulations of 2,4-D esters are distributed uni-
formly over the water surface at rates of 10 to 40 Ib/acre. Amine salts are probably more often
applied as sprays over the water surface or injected beneath the water surface.
The toxicity of 2,4-D to fish is extremely variable. The ester derivatives as a group are the
most toxic. However, the formulating components are an important factor in acute toxicity to fish
(Walker, 1964a and 1964b). In laboratory assays, some toxicity to fish occurs at approximately the
maximum recommended treatment rates (Lawrence and Hollingsworth, 1969; Walker, 1969).
Under field conditions, toxicity at maximum recommended rates has seldom if ever been observed
and can be avoided with proper precautions. Any adverse effects on the aquatic environment are
primarily the result of habitat modification. Temporary effects are not severe, nor is the damage
extensive. 2,4-D should not be used in potable water where the residue would exceed 0.1 ppmw.
Silvex.—The potassium salt of Silvex is applied as a liquid or used occasionally in granular or
pelleted formulations (DeVaney, 1968; Walker, 1969). It is, as a rule, somewhat more persistent in
the aquatic environment than 2,4-D (Menzie, 1969). It is also slightly more phytotoxic than 2,4-D
to some aquatic plants. Because of its greater cost and its limited advantage over 2,4-D, Silvex is
seldom used. The recommended application rates are 1.5 to 2 ppmw, or about 5 Ib per acre-foot of
water. Other observations concerning 2,4-D also apply to Silvex.
Other Herbicides.—Other herbicides used infrequently for the control of submersed weeds in
ponds, lakes, and reservoirs are acrolein and aromatic solvents. Because of their toxicity, they are
normally used for spot treatments. The discussion on page 131 concerning the use of acrolein and
aromatic solvents in irrigation ditches also applies to their use in ponds, lakes, and reservoirs. Sima-
zine and diuron have been used experimentally in extensive testing to control pH and reduce plant
biomass responsible for oxygen-depletion hazards in ponds used for fish production. Increases in pH
and oxygen levels are highly desirable, and appreciable toxicology and residue research is being con-
ducted on these herbicides to support registration for their use.
Emersed and Marginal Weeds
Emersed weeds are common to shallow bodies of water and shallow, slow-moving streams.
Because most are littoral species, they are an important component of the habitat for fish and other
aquatic animal life and play an important role in the aquatic food chain. The location of these
weeds makes them especially undesirable to lakeside homeowners, swimmers, and other water users.
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Marginal weeds are very often grasses or grasslike species. They are often more troublesome
than emersed weeds. Many are tall enough to obscure the view of the water, and they impede
access to the water. Some are capable of causing severe lacerations, and they provide a habitat for
snakes, vermin, and other undesirable animals. If undisturbed, many will encroach on the water
surface and prevent the use of much of the surface areas of small lakes and ponds.
Broadleaved Plants
2,4-D.— As a general control for most marginal and emergent broadleaf vegetation, 2,4-D at 2 to
4 Ib/acre is commonly recommended (DeVaney, 1968). It is applied in a sufficiently large volume
(up to 200 gal/acre) of water to wet the entire exposed plants. For hard-to-wet species of plants
with waxy leaves (e.g., as waterlilies, smartweed, waterprimrose, and arrowhead (Sagittaria spp.))
better results are obtained by spraying the plants with 2,4-D in oil or in an oil-in-water emulsion (1
to 2 parts oil in 10 to 20 parts water). 2,4-D is applied at 1 to 4 Ib/acre in a volume of carrier that
will provide a uniform spray cover.
Silvex.—As a general control, Silvex is used in the same manner as described for 2,4-D. Rooted,
emersed alligatorweed is treated at 4 to 8 Ib/acre. Repeated treatments (three to four) may be re-
quired for control.
Grass and Grasslike Species
Dalapon.—Most grasses and grasslike plant species, including cattails and bulrushes, respond
well to treatments with dalapon at application rates of 20 to 30 Ib/acre. Application should be
made before the plants are fully grown and before heading. A large enough volume of water is used
to wet the foliage thoroughly. Wetting is aided by the addition of 3 to 4 pints of wetting agent for
each 100 gallons of water. Repeated light applications of 5 to 10 Ib/acre are more effective on
some species of grasses.
Dalapon is registered for use only in drainage ditches and marshes. It is currently replacing
amitrole for the control of grasses on ditchbanks and other sites where amitrole was formerly used.
Acute toxicity to fish occurs only at very high concentrations (the TLm concentration for salmon
after 48 hours is 340 ppmw) (Lawrence and Hollingsworth, 1969; Pimentel, 1971). Studies to date
indicate no adverse effects on the aquatic environment other than those associated with habitat
modification (Walker, 1972). No direct effects or residue problems are likely to occur from the
concentrations in water following recommended uses.
2,4-D.—Low-volatility esters of 2,4-D applied at 4 to 6 Ib/acre in 1:20 oil-in-water emulsions
may be substituted for dalapon for the control of bulrushes and cattail (DeVaney, 1968). The
volumes of spray recommended to get thorough wetting of the foliage are 150 to 300 gal/acre. As
with other grass treatments, the first application should be made at or before heading of the plants.
Repeated treatments (three to four) of regrowth may be required for complete control.
MSMA and TCA.— Neither MSMA (monosodium methanearsenate) nor TCA (trichloroacetic
acid) is registered for use in or around water. Both have been field tested extensively and appear to
have desirable uses for the control of ditchbank grass weeds. At application rates of 20 to 70 lb/
acre, TCA controls reed canarygrass; MSMA is the only herbicide that appears capable of controlling
johnsongrass on ditchbanks in the Southwestern States where TCA is not effective.
Alternative Methods of Aquatic Vegetation Management
Mechanical Methods.—Various mechanical contrivances have been designed and used in
attempts to manage troublesome growths of aquatic plants. Those designed for use in impounded
waters and streams are primarily of two types: (1) underwater cutters to sever submersed vegetation
and (2) devices for cutting swaths from floating vegetation such as waterhyacinth. Both types have
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been constructed at various times for simultaneously cutting and removing plants from the water.
Simply cutting the plants off at some depth below the surface is not a practical solution. The float-
ing plants drift about, causing new infestations; they continue to hinder use of the water; they float
ashore, where they may decay and produce an objectionable appearance and foul odors; and they
eventually die and may cause localized fouling of the water that is detrimental to all aquatic animal
life.
Harvesters designed to cut and remove plant material from the water have been in existence for
many years. The U.S. Army Corps of Engineers pioneered in the design and construction of such
machines. Although effective, they are costly to construct, operate, and maintain. In addition,
they are limited to easily accessible waters free of obstructions and to areas they can clear in a given
period. Harvested plant material must be disposed of in some manner. Disposal is a serious
problem that has not been solved.
The greatest obstacle to mechanical control of aquatic plants in any situation is cost. It was
stated recently that "... with existing mechanical harvesters tested to date the cost is as much as
$1,600 per acre (depending upon area of use) to eliminate an acre of hyacinth as compared with a
chemical treatment cost of about $12 per acre (USA'CE, 1972). Other estimates for mechanical
removal of waterhyacinth range from $150 to $1000 per acre. Harvesters average about 4 acres per
day.
Equipment for mechanically controlling aquatic plants in irrigation systems ranges in form
from underwater weed cutters and draglines to large chains and disk-type devices. In irrigation sys-
tems the principal concerns regarding the use of mechanical methods of control are similar to those
encountered elsewhere—cost and the amount of time involved. In addition, the masses of material
produced by mechanical control clog screens and trash racks, siphons, headgates, and sometimes
water-measuring devices. The operation of sprinkler systems is also seriously affected. The use of
chains and disks disturbs the soil and hastens the buildup of silt bars, which when removed by drag-
line can be very destructive to fish habitats. There is very little good that can be said for the me-
chanical control of weeds in irrigation systems, drainage ditches, or navigation canals. It is much
less desirable in these sites than in impounded waters or large natural streams.
Biological Methods
Fish, Snails, and Other Aquatic Animals.—Herbivorous fish are especially attractive as biologi-
cal control agents (Avault et al., 1966; Sills, 1970). This is particularly true for species that are
acceptable as sporting fish and can be utilized for food. At present very limited use is being made
of fish to control aquatic weeds. Florida and California are now using Tilapia spp. in a few aquatic
sites, but the growth rates and fecundity of the fish may not be desirable. These fish are also sensi-
tive to low temperatures and will not survive winter weather in most areas of the United States.
The most promising of all herbivorous fish tested is the grass carp, or white amur, which is
presently undergoing study at several locations (Stevenson, 1965). It tolerates a wide range of
temperatures and consumes many different species of plants (Michewicz et al., 1972). It has been
cultured in various European and Asian countries for both weed control and food, but little investi-
gation into its ecological impact on other species has been undertaken (Hutt, 1971; Pelzman,
1971). There is a great deal of reluctance and resistance to the release of this fish in the United States
because of fears that it may become a troublesome pest similar to the common carp (Sneed, 1971).
State workers in Arkansas have made experimental stockings of the white amur in many of the
state's natural lakes (Bailey, 1971). Because of its potential as a biocontrol agent, this large fish
must be studied carefully and thoroughly by public agencies and released only if it will not present
a hazard to the aquatic environment. Its reproduction and growth must be controllable if it is to be
used at stocking rates that are balanced in relation to weed growth. As in the case of chemical resi-
dues, we can ill afford "biological residues that multiply"; thus the reproduction and distribution of
the fish must be strictly controlled.
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Various snails also consume aquatic plants. One species that received considerable attention is
the marisa snail (Marisa cornuarietis L.). It is, like many of the tropical herbivorous fish, very in-
tolerant of low temperatures. Although it avidly consumes aquatic vegetation, it will overwinter in
few if any locations in the United States. Mass-rearing techniques developed by the University of
Miami under contract with the Agricultural Research Service indicate that the snail could be
propagated at a cost of 0.6 cent each if produced at an annual rate of 12 million. The high stock-
ing rates required for the control of aquatic plants make the cost of propagating and utilizing the
snail impractical in most waters.
Other aquatic animals, such as the crayfish (Orconectes causeyi), have been considered as pos-
sible biological control agents. However, only limited tests have been conducted to date, and results
are somewhat variable from area to area (Dean, 1969).
Insects.—Although studies in this very important phase of aquatic vegetation management have
been minimal, there have been several significant developments in recent years. One was the intro-
duction of the Agasicles flea beetle for the control of alligatorweed (Maddox et al, 1971). Since its
introduction, it has become established from Georgia to Texas and has become an important factor
in the control of this weed. Its range is quite restricted in latitude; however, there is some evidence
that by using the beetle in conjunction with chemicals, its effective range may be extended to
almost the entire range of the weed.
Other promising insects being released are a species of thrip (Amynothrips andersoni) and a
moth (Vogtia malloi), both parasitic on alligatorweed.
Pathogens.—There is considerable conjecture but little data concerning the role of pathogens in
the ecology of aquatic plant communities. Massive kills of aquatic plants are observed periodi-
cally. Striking examples occurred recently with Eurasian watermilfoil in estuaries (e.g., the Chesa-
peake Bay) and with eelgrass (Zostera marina) along the Atlantic Coast. The epidemiclike affliction
of these weeds led observers to postulate the presence of pathogens (possibly viral). A search for
pathogens of several troublesome species of aquatic plants is currently being made by workers at the
University of Florida as well as other investigators. The potential and desirability of aquatic vegeta-
tion management by the use of pathogens warrants much greater emphasis than is currently given to
this area of research.
Competitive Vegetation.— Competition among plants for specific ecological niches often deter-
mines the composition of plant communities and the distribution of species. All too often the least
desirable species are the most effective competitors. The principle of competition, frequently used
in agriculture, is put to good advantage in the management of ditchbank and marginal aquatic
plants, where desirable species of grasses are aided by chemicals in establishing positions of domi-
nance. Progress has been made in the last several years in the use of very low growing aquatic
species (e.g., pigmyweed (Tillaea aquatica) and spikerush (Eleocharis spp.)) as competitive plants
(Yeo and Fisher, 1970). This research (conducted by the Agricultural Research Service at Davis,
California) has resulted in establishing effective control of troublesome aquatic plants in a number
of canals and lakes. Because this type of vegetation management reduces or eliminates the use of
chemicals, it should receive a high priority in research programs.
Ecological Modification.—Very little research has been done to determine the potential of
ecological modification as a tool in the management of aquatic vegetation. Many species exist and
thrive within a very narrow range of ecological conditions. Modifying or disrupting a single condi-
tion or requirement of the plant may be sufficient to eliminate a species or to reduce the magnitude
of its contribution to an undesirable aquatic environment.
Advantages and Disadvantages of Chemical Methods
Efficacy of Chemicals versus Alternatives.—There are few instances in which the efficacy of
chemicals has not exceeded that of presently available alternatives for aquatic plant control. Cover-
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ing or enclosing irrigation distribution systems in pipe is an effective means of eliminating weeds in
irrigation canals. At present, the construction of new open systems on U.S. Bureau of Reclamation
projects must be justified as alternatives to enclosed systems. Closed systems, though not plagued
with weeds, are subject to other problems, such as silting and infestation with clams, bryozoans, and
freshwater sponges.
In the narrow band of the Southern United States to which it is climatically suited, the
Agasicles beetle has proved superior to chemicals for controlling alligatorweed. Outside this
narrow range, however, populations of the beetle do not reach the levels necessary to hold alligator-
weed in check.
Chemicals remove aquatic vegetation more completely and more quickly than does mechanical
control, which is the only alternative method that has or might be used extensively at this time.
Underwater cutters and harvesters are unable to clear more than a few acres of weeds per day and
are restricted to unobstructed areas. Fixed-wing aircraft, helicopters, and boat-mounted sprayers
can treat many times this area. During the mechanical removal of weeds, the plants are usually frag-
mented. The fragments are often moved about by wind and currents and initiate infestations in
new areas. Chemicals are for the most part nonselective in the plants removed. Furthermore, they
are difficult to confine to specific areas, and partial treatment of a body of water frequently results
in the temporary but total removal of all the aquatic vegetation. Phytoplankton, often as trouble-
some in some waters as vascular aquatic plants, can be eliminated effectively only by chemicals.
As an alternative to herbicides, water-level manipulation is an effective control measure. Un-
fortunately, levels in few bodies of water or streams can be varied to this extent. Weed growth in
the shallows of some TVA impoundments can be eliminated by manipulating the water levels at
certain periods.
Preventing eutrophication and reducing the levels of nutrients in water, although not effective
in eliminating plant growth, would reduce the rates of weed growth and the total mass of plant
material present in the water at any given time. Most sources of nutrients are runoff from farmland,
domestic sewage, and certain industrial wastes. It is unlikely that plant nutrients from these sources
will be significantly curtailed or eliminated in the near future.
In spite of current fads for alternative measures, chemical control methods will be necessary as
part of any realistic pest-management program that involves integrated systems of mechanical, cul-
tural, biological, or ecological modification as techniques (Walker, 1972).
Environmental Consequences
Agriculture.—The injurious consequences of using herbicides to control aquatic vegetation,
insofar as they affect agriculture, are neither serious nor frequent. Because of the proximity to
agricultural activities, it would be natural to assume that hazard levels would be greatest in irrigated
agriculture. However, after 25 years or more of using such herbicides as copper sulfate, aromatic
solvent, and 2,4-D for the control of submersed and marginal weeds in irrigation systems, there have
been very few substantiated instances of injury to crops or to livestock. Livestock will not drink
water containing potentially harmful levels of acrolein or aromatic solvent.
The residues of other herbicides used in irrigation water are so low that the infrequent and
short-term exposures make it virtually impossible for livestock to ingest quantities that would be
toxic or cause residue problems in meat, milk, or other agricultural products (Anon., 1968). Simi-
larly, the low levels of 2,4-D, TCA, dalapon, and other herbicides used on irrigation systems (Frank
et a/., 1970) cause neither injury (Bruns, 1954 and 1957; Bruns and Clore, 1958; Bruns and
Dawson, 1959) nor illegal residues in crops (Stanford, 1970; Frank and Demint, 1969/1970 and
1971). Normal weed-control procedures result in the deposition of only a few grams of herbicide
per acre; only under experimental conditions involving exaggerated rates of herbicides is it possible
to find more than traces of herbicides in irrigated crops. Herbicides are rarely employed in major
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impoundments of agricultural water. More frequently, they are used in private, multipurpose farm
ponds, where the potential for herbicide misuse is greatest. Nevertheless, with proper use and the
observance of water-use restrictions after application, the hazards are minimal.
Perhaps the most evident and publicized hazard to the environment is the improper use of
herbicides like 2,4-D in the vicinity of susceptible crops and other desirable plants. Problems of
spray drift and vapors, though much reduced at this time, were experienced frequently in the past.
Recreation.—The environmental consequences of using herbicides in water are potentially
greater for recreation than for agriculture. All water (streams, ponds, lakes, or reservoirs) offers
some possibility for recreational use. Because of the wealth of water in most areas of the United
States, access to water for recreation was plentiful in the past. The greater population and the
development of waterfront property have significantly reduced the opportunities and ease of
access. Greater effort is required to improve and maintain the quality of water used for recreation.
At present chemical control is the most feasible means of accomplishing this on the scale required.
The consequences of herbicide use may be good or bad. Used properly, herbicides can provide
greater expanses of open water for swimming, boating, skiing, fishing, and other activities. They
can to some extent retard the process of eutrophication and extend the useful life of lakes and
ponds. Vegetation that aids the breeding of mosquitoes and harbors other insects, as well as snakes
and vermin, can be removed, with subsequent improvement of the aquatic environment for recrea-
tion.
Adverse or controversial effects on certain recreational uses of the aquatic environment can be
anticipated. By management of the aquatic vegetation, water may be converted from such uses as
fishing or waterfowl habitat to water used primarily for swimming, boating, and skiing. Such con-
versions raise controversy due to conflicts of interest depending on the recreational needs or desires
of individuals. The control of aquatic plants with certain herbicides requires the interruption of
some water uses for specific periods, usually when the recreational needs for water are greatest.
This is a major inconvenience to vacationers.
Persistent use of herbicides may have long-term effects on the ecology of aquatic sites. These
ecological systems are exceedingly complex and variable even when unmolested. The ecological
modifications resulting from the use of herbicides may be far reaching and at this time can only be
surmised.
Fisheries Management.—Without the use of chemicals for controlling the growth of aquatic
plants, the ecological consequences related to fisheries management can be disastrous (Walker,
1971). Usually, the ecological succession of aquatic plants results in the overwhelming predomi-
nance of a few plant species that exhibit a pattern of seasonal succession. The primary purpose of
herbicide use is to modify plant succession and the seasonal distribution of biomass and its species
composition (Walker, 1972). When this vegetation becomes dense, there is always a high probabil-
ity of summer or winter fish kills as a result of oxygen depletion when the plants die and decay
(Walker, 1969).
Direct toxicity to aquatic animal life is not a serious problem with most herbicides or algicides
(Condon, 1968; Lawrence and Hollingsworth, 1969; Walker, 1969; Tucker and Crabtree, 1970;
Battelle, 1971; Pimentel, 1971). Fish and many other aquatic fauna vary in their sensitivity to low
oxygen tension, and to poisoning by hydrogen sulfide, ammonia and a variety of other nitrogenous
compounds, and other products of decomposition.
Very few alternatives to chemicals exist for effective plant control (Walker, 1969). Mechanical
control with weed cutters is restricted to unobstructed areas and to deeper water. Mowing frag-
ments many species, causing more propagules to be formed; this provides .an advantage to weeds
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that are capable of rapid regrowth and establishing dominance over other species. The cultivation of
monospecies vegetation is an adverse ecological consequence that is just as serious as no control.
The removal of plant biomass by mechanical means has the distinct advantage of interrupting nutri-
ent recycling, thus decreasing the burden of decomposed organic matter (and the attendant oxygen
depletion), the deposition of organic debris, and the processes of eutrophication. Biological con-
trol, where effective, is advantageous in that nutrients are recycled into other food chains. Such
recycling is most desirable when it leads to the production of food that can be harvested or contrib-
utes directly to greater recreational use of water. However, the most realistic approaches to aquatic
plant control require the integrated use of chemical, mechanical, and biological methods that
provide satisfactory long-term management of the troublesome aquatic vegetation.
Wildlife Management.—The ecological consequences of controlling aquatic plants by chemical
means may affect wildlife indirectly by modifying the habitat. Chemical control may have an ad-
verse effect if it destroys plants that are valuable for food, nesting, rearing, roosting, or protection.
Mechanical control can be far more disruptive than chemicals with respect to the needs and activ-
ities of wildlife. The temporarily adverse effects of herbicide chemicals on water quality and the
growth, regeneration, and general suppression of the plant biomass may be more critical for some
wildlife species than others. Thus particular care must be taken in areas where habitat preservation
is required for the welfare of rare and endangered species. Direct toxicity of herbicides to wildlife
has never been a problem (Condon, 1968; Lawrence and Hollingsworth, 1969; Tucker and Crabtree,
1970; Battelle, 1971; Pimentel, 1971); however, we have insufficient data with respect to residues
and their biological significance. Similarly, the adverse effects of mechanical control and biological
control agents have not been evaluated critically.
Property Values.—The value of waterfront property would be enhanced by the use of herbi-
cides to control serious infestations of floating, submersed, or marginal aquatic weeds. The princi-
pal concern of property owners is that the water be clean and open; other attributes rarely have
greater priority.
Potable Water Sources.— Eutrophication processes take their toll on the quality of potable
water. Very often this is demonstrated first by the abundance of algae. Infestations of algae can be
managed successfully with a carefully planned program employing copper sulfate. Storage lakes and
reservoirs not previously containing excessive growths of vascular aquatic plants are now experi-
encing an increasing abundance of these weeds. Also, the increasing need for potable water has
forced the utilization of less desirable water sources. Large quantities of vascular weeds have a
strong polluting effect during certain times of the year. These circumstances have forced the use of
herbicides, in addition to copper sulfate, in a number of sources of potable water. This practice or
more extensive use of mechanical harvesters will increase as weed problems become more severe.
Navigation.—Large quantities of herbicides are used in the Southern States to keep waterways
open to navigation. It is estimated that, if chemical control were discontinued, within a 2-year
period a high proportion of these waterways would no longer be navigable. During the past 2 years
the U.S. Army Corps of Engineers, at the request of certain groups and individuals, carried out a
modified chemical weed-control program on the St. Johns River in Florida. Only selected areas and
infestations of waterhyacinth were treated with herbicides. This program, combined with a mild
winter (1971-1972) that permitted greater than normal growth of hyacinth, resulted in an infesta-
tion that by the summer of 1972 was completely out of control. It was estimated that 10,000 acres
or more of waterhyacinth were descending the St. Johns River. Navigation in some areas was total-
ly blocked; it was reported that bridges were in danger of being carried away; and the fishing in-
dustry in much of the area was disrupted. Navigation in the waterways of more northerly states
may be impeded by weed growths; however, the problems are less serious and are usually limited to
the smaller waterways and portions of water impoundments.
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The use of herbicides to clear navigable waters has favorable environmental consequences inso-
far as navigation is affected. There are numerous and persistent complaints that chemical control
programs seriously impair fishing. Some complainants state categorically that the herbicides poison
the fish. Although sinking mats of dead or decaying vegetation do cause oxygen depletion and re-
lease noxious gases and metabolic products, the residues of aquatic herbicides have rarely been
found to be poisonous. There is little doubt that the removal of weeds affects fishing and particu-
larly fishing customs. The disappearance of weeds alters the habitat as well as the source of fish
food (Walker, 1969). In large water systems this causes major shifts in fish populations and den-
sities, which are frequently mistaken for direct chemical effects on the fish (Walker, 1972). Delete-
rious effects on the fish and fishery may occur. These are likely to be indirect and may be quite
complex. Because aquatic ecology is exceedingly complex, there are no quick or easy answers to
questions regarding the overall or long-term effects of herbicides on fish or other aquatic fauna.
Herbicide Residues in Water
Control of Submersed Weeds.—The initial concentrations of herbicides used in water to control
submersed weeds are usually determined before treatment. If the water volume and area are care-
fully measured, the concentrations are usually within an acceptable range of error. The concentra-
tions employed are determined by the particular herbicide used and the species of plants being
treated. The more commonly used herbicides and recommended application rates are listed in
Table 6. Data from some of the more typical studies on the dissipation of herbicide residues in
water are compiled in Table 7.
Table 6. HERBICIDES AND APPLICATION RATES RECOMMENDED FOR
THE CONTROL OF SUBMERSED AQUATIC WEEDS
Herbicide
Acrolein
Aromatic solvents
Copper sulfate
Dichlobenil
Diquat
Endothall
Fenac
Form
Liquid
Emulsified
Pentahydrate
Granular
Cation
Disodium salt
Amine salt
Granular
Application rate1
0.1 to 0.6 ppm2
4 to 7 ppm3
600 to 740 ppm4
0.1 to 2 ppm
10 to 15 Ib/acre
0.9 to 1.4 ppm5
0.25 to 1.5 ppm
0.5 to 4 ppm
0.05 to 2.5 ppm
15 to 20 Ib/acre
1.4 to 1.8 ppm5
Silvex Potassium salt 1.5 to 2 ppm
2,4-D, ester Granular 20 to 40 Ib/acre
1.8 to 3.6 ppm
5
'Source: USDA (1969). Application rates are in terms of acid equivalent or active
ingredient.
2 For extended application time in flowing water.
3 For treatment of weeds in quiescent water.
4Emulsifier added at concentrations of 1.5 to 2 percent.
5Parts-per-million concentration arbitrarily expressed in terms of 4 feet of water.
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Table 7. RESIDUE DISSIPATION IN PONDED WATER AFTER HERBICIDE APPLICATION
Herbicide
Application
rate
(ppm)
Concentration detected
Highest Final
ppm Days ppm
Days
Amitrole1
Fenac1
Diquat1
Paraquat1
2,4-D, methylamine salt2
Silvex, PGBE ester3
Diquat4
Paraquat4
Endothall4
Copper5
Endothall6
Liquid applications
1.0 1.34
4.0 5.2
2.5 3.27
2.1 1.05
1.5 0.139
2.9 1.6
0.62 0.49
1.14 0.55
1.0 0.18
0.50 0.42
1.2 0.79
1.0
1.0
2.0
1.0
1.0
7.0
1.0
1.0
2.0
0.1
4.0
0.08
2.4
N.D.
N.D.
0.004
0.02
0.001
0.001
0.001
0.19
0.54
201
202
30
38
41
182
8
12
36
3
12
Granular applications
Dichlobenil4
Fenac4
2,4-D, butoxyethanol ester4
0.58
0.40
1.56
1.0
1.33
0.32
0.23
1.61
0.71
0.067
36
8
18
8
18
0.004
0.001
0.38
0.07
0.001
160
160
160
160
36
1 Data from Grzenda eta/. (1966).
'Data from Averitt (1967).
3 Data from Cochrane et al. (1967).
4Data from Frank and Comes (1967).
'Data from Toth and Riemer (1968).
6 Data from Yeo (1970).
Some of the more effective herbicides are also among the more persistent (Menzie, 1969). The
excellent and often complete control of weeds by fenac and dichlobenil may be attributed in part
to the persistence of these herbicides. Diquat, 2,4-D, and endothall disappear from water at rapid to
moderate rates. Although rapid dissipation from water is desirable from the standpoint of residues,
it may impair or destroy the efficacy of some chemicals (e.g., diquat) when used in water containing
sediment or organic matter. In some instances, the dissipation of herbicides from water may be
accompanied by accumulation of high concentrations of the herbicides in the soil (Frank and
Comes, 1967).
The dissipation of herbicides in the flowing water of canals and streams has not been studied
extensively. However, from experiments carried out during the last several years (Frank et al.,
1970), it is apparent that the dissipation (in flowing water) of freely water soluble herbicides not
extensively sorbed from water solutions is affected principally by dilution. For nonvolatile herbi-
cides, extrapolation of residue and dissipation data (Table 8) indicates that for most canal-bank
treatments for marginal weeds, the herbicides that enter the water dissipate to trace levels after a
waterflow of about 20 miles.
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Table 8. MAXIMUM LEVELS OF HERBICIDE RESIDUES FOUND IN
IRRIGATION WATER DURING DITCHBANK TREATMENT1
Herbicide and
canal treated
Dalapon:
Lateral No. 4
Manard lateral
Yolo lateral
TCA:
Lateral No. 4
Manard lateral
Yolo lateral
Treatment
rate (Ib/acre)
6.7
9.6
10.5
3.8
5.4
5.9
Water flow
(ft3 /sec)
290
37
26
290
37
26
Maximum concentration
of residue (^g/l)
23
39
162
12
20
69
2,4-D, amine salt:
Lateral No. 4 1.9 290 5
Manard lateral 2.7 37 13
Yolo lateral 3.0 26 36
'Source: Frank etal. (1970).
Data showing residue levels and dissipation rates typical of aromatic solvent (xylene) treat-
ments in irrigation canals are given in Figure 1. The persistence of acrolein residues appears to be
temperature dependent, but very few accurate determinations are available. The loss rates of acro-
lein from concentrations of 0.6 and 0.7 ppmw in a canal with a flow of 132 to 135 ft3/sec were
determined to be 98 percent from 64°F water after a waterflow of 19 miles and 62 percent from
48°F water after a flow of 27 miles (Battelle, 1970).
Control of Floating Weeds.— Residues in water due to the application of herbicides to floating
weeds are difficult to determine. On the basis of the rates of application and the depth of water,
total possible residues may be calculated. These are seldom realistic because the vegetation inter-
cepts a significant fraction of the total herbicides applied. Residues of amine salts of 2,4-D and
Silvex in water are highest 1 to 2 weeks after the treatment of alligatorweed (Averitt, 1967).
Almost all published data concerning residues in water from the treatment of floating vegetation
show that even at high rates (8 Ib/acre), residue levels will usually be less than 1.5 ppmw.
Potable Water.—Only two herbicides have been assigned tolerance levels in potable water:
2,4-D amine (0.1 ppmw) and copper sulfate (1 ppmw copper ion). This level of copper sulfate is
higher than that used in most instances for algae control. The level of 0.1 ppmw of 2,4-D would
very likely be exceeded in most instances when used for the control of aquatic plants. Possible ex-
ceptions might be low rates (1 to 2 Ib/acre) sprayed on solid mats of floating weeds (e.g., water-
hyacinth). Consequently, 2,4-D or other herbicides should be used under circumstances that will
permit dissipation to acceptable levels before the water reaches outlets to water-treatment plants.
Fish and Wildlife.—Herbicides residues are seldom found in fish collected from the wild, but
very few analyses have been specifically directed toward their detection (Walker, 1964b, 1969, and
1971). As a group, herbicides are less persistent than organochlorine insecticides (Stickle, 1968).
They do not "biomagnify" as readily in food-chain organisms or cause high residues in fish because
they have a different partition coefficient or fat solubility (Walker, 1964b; Grant and Schoettger,
1971). In the most severe cases of herbicide-residue accumulations in fish, the levels are usually
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600
500
| 400
X
| 300
200
100
Sampling Distance
Downstream From
Point of Application
O 0.25 Miles
• 0.5 Miles
• 2.5 Miles
A 6.5 Miles
D 9.0 Miles
1.0 0.75 0.5 0.25 0 0.25 0.5 0.75 1.0
Sampling Distance from Midpoint of Treated Body of Water in Miles
Figure 1. Graphic illustration of the longitudinal dispersion of a 700-ppm application of xylene.
The effect of dilution and "stretch-out phenomenon" reduced the concentration at sam-
pling points downstream as measured with reference to the midpoint of application in
the stream flow.
quite comparable to the concentrations in the water, and they dissipate rapidly as the source dimin-
ishes (USDA, 1963; Walker, 1972). Such is the case with dichlobenil, simazine, diuron, 2,4-D, and
Silvex. Fish can hydrolyze or metabolize most herbicides, and the metabolites, conjugates, and
breakdown products are readily excreted (Walker, 1964b; Menzie, 1969). Residues have not yet
presented problems in other wild animals but would be expected to follow patterns similar to those
observed in livestock and poultry (Menzie, 1969).
Crops.—Illegal or unacceptable residues in crops stemming from the use of water containing
herbicides have not been a problem. Herbicide concentrations high enough to produce significant
levels of residues in crops would very likely kill the crop plants, particularly those that are irrigated
with sprinkler systems. Some data on the levels of residues in crops irrigated with water containing
herbicides are shown in Table 9. The concentrations of herbicides were usually below the minimum
levels of detection. Where residues were detected, they were below the tolerances now established
for them in food and feed crops.
Livestock.—Most herbicides ingested by livestock are excreted in a short time. Unlike insecti-
cides, they do not accumulate in fats; consequently, there is no buildup of residues. Ingestion in
sufficient quantities may result in residues in milk and eggs. Except for aromatic solvent, recom-
mended uses of herbicides produce residues in water ranging from a fraction of 1 ppm to several
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Table 9. RESIDUES IN CROPS IRRIGATED WITH WATER CONTAINING HERBICIDES1
Residues in crops (ppm)
^rop ana metnoa OT
irrigation
Carrots:
Furrow
Sprinkler
Grain sorghum:
Furrow
Sprinkler
Lettuce (Romaine):
Furrow
Sprinkler
Onions:
Furrow
Sprinkler
Potatoes:
Furrow
Sprinkler
Soybeans:
Furrow
Sprinkler
Dalapon
(0.1-2.5lb/acre)
0.56
0.42
0.05
0.11
0.88
1.13
0.46
0.67
0.03
0.04
0.20
0.20
Diquat
(0.1 0-0.5 Ib/acre)
<0.05
<0.05
<0.10
<0.10
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.10
<0.10
Dichlobenil
(0.1 -0.5 Ib/acre)
<0.05
<0.05
<0.02
<0.02
<0.01
<0.01
<0.02
<0.02
--
<0.05
<0.05
2,4-D
(0.05-0.25 Ib/acre)
0.03
0.06
<0.05
<0.05
0.14
0.11
<0.01
<0.01
0.03
0.05
<0.05
<0.05
Silvex
(0.05-1. 5 Ib/acre)
<0.05
<0.05
<0.05
<0.05
<0.05
<0.'05
0.03
0.03
0.03
0.04
0.14
0.11
'Source: Stanford Research Institute (1970).
ppm. At these concentrations, it is virtually impossible for livestock to consume large enough
volumes of water to accumulate residues.
Toxicity Hazard
Livestock.—To date there have been very few proved cases of livestock poisoning from any
pesticides and even fewer cases involving aquatic herbicides. The instances of toxicity reported
were attributed to human negligence or accident.
Fish.—Information on the toxicity of herbicides to fish and other aquatic organisms is mainly
derived from laboratory bioassay tests involving sterile, artificial environments (Lawrence and Hol-
lingsworth, 1969; Walker, 1969; Pimentel, 1971). These tests are rarely conducted in the presence
of aquatic vegetation, soil, suspended sediments, and other substances that interact in the absorp-
tion/desorption kinetics or in degradation/detoxification mechanisms (Walker, 1964b). Conversely,
less-informed individuals may also translate TL50 values and toxicity measurements from short-
term bioassay tests into "safe" concentrations when these data are not applicable and certainly not
to be misconstrued as "ecologically safe or nonhazardous" (Grant and Schoettger, 1972). Com-
pared to other pesticides (insecticides, fungicides, etc.), herbicides are much less toxic to fish and
aquatic fauna (Walker, 1964b; Grant and Schoettger, 1972). When used according to directions,
presently labeled herbicides seldom cause extensive or lasting injury to nontarget organisms in fish
habitats (Walker, 1972). Care must always be exercised to ensure that too large a mass of dead or
dying vegetation does not deplete the supply of dissolved oxygen or result in an excessive
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production of toxic gases (i.e., hydrogen sulfide) or other toxic byproducts (ammonia, hydroxyl-
amines, etc.) (Walker, 1969).
Some fish kills can result from the direct toxicity of herbicides like acrolein, dichlone, xylene
(petroleum distillates), alkylamine salts of endothall, and combinations of copper with diquat or
endothall when used without regard for fishes (Walker, 1969; Pimentel, 1971). Even here, partial
treatments that allow for adequate dilution, buffer zones, and care in driving fish out by initiating
treatment at lower concentrations that repel fish will avoid many toxicity problems (DeVaney,
1968). The selection of less toxic formulations, such as the amine salts of 2,4-D rather than the
more toxic esters, can minimize hazards to fisheries (Walker, 1964a).
Water volumes, rates of flow, circulating currents, tidal action, and other simple factors are
important considerations in the use of herbicides (Walker, 1969). Unfortunately, placement of
herbicide on the target is difficult and is a basic problem in avoiding hazardous effects on nontarget
organisms (Walker, 1964b; Pimentel, 1971). However, newer developments in granular formula-
tions, encapsulations, and other slow-release formulations permit on-target application with longer
herbicide-contact time and lower levels of exposure to fishes, shellfishes, and other nontarget orga-
nisms. Direct conflicts of purpose sometimes occur when algicides destroy valuable plankton
species or when some aquatic plant growth is desirable for fish-food organisms. These instances of
conflict involve the total elimination of vegetation by nonselective herbicides (Walker, 1964b).
Wildlife.—As with fish, the toxicity of herbicides to wildlife is not direct but is related to the
indirect effects of habitat modification. The drift of herbicides onto desirable marginal vegetation
or contamination of water flowing into waterfowl-food-bearing areas are obvious problems that can
be avoided by proper management. Direct conflicts do exist when valuable waterfowl foods (such
as pondweeds, naiads (Najas spp.), and duckweed) are the targets of herbicide application. Thus
nesting cover or critical food organisms for young birds are destroyed, and failures in reproduction
occur in the treated area. Destruction of protective cover may open up areas, leaving wildlife vul-
nerable to predation. Moreover, some pathogenic organisms may thrive under the septic conditions
produced by decaying vegetation.
Crops.—For algae control copper sulfate is used most frequently at concentrations that are no
greater, and often lower, than the tolerance level established for this herbicide in potable water
(USDA, 1963). Xylene is a common formulating ingredient for many pesticides and as such is often
applied directly to crop plants. The distribution of irrigation water containing acrolein by furrow
or sprinkler contributes to the rapid loss of this herbicide. Copper sulfate, xylene, and acrolein are
of minor importance as sources of toxicity to crop plants.
When used as directed, other herbicides are present in irrigation water at levels that are not
toxic to crops. We can calculate the maximum amount of a herbicide like 2,4-D that might be
applied to cropland after its use on an irrigation canal bank. Water from a 4-mile-long body of irri-
gation water flowing at a velocity of 1 mph could be diverted onto an adjacent field for 4 hours. A
diversion rate of 2 acre-inches of water in 10 hours would result in the delivery of 0.8 inch of con-
taminated water (4 hours at the rate of 2 inches per 10 hours) per acre. An 0.8-inch depth of water
containing 50 ppb of 2,4-D (a higher concentration than that usually observed) would deposit
slightly less than 0.009 pound of 2,4-D per acre of cropland. Residue levels of much greater magni-
tude have not caused injury to irrigated crops.
The manner in which irrigation water containing herbicides is applied to cropland may in-
fluence the levels of herbicides that are toxic to crops. Obviously, sprinkler irrigation of crops like
lettuce and sugar beets with water containing 2,4-D will result in toxicity at lower levels of contami-
nation than would occur if the water were applied by furrow. Considerable data have been pub-
lished concerning the toxicity of herbicides in irrigation water (Bruns, 1954 and 1957; Bruns and
Clore, 1958; Bruns and Dawson, 1959; Averitt, 1967). Other studies are in progress or have been
completed but not yet published.
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Social and Economic Impact of Restricting the Use of Aquatic Herbicides.—With the exception
of copper sulfate, the aquatic herbicides currently being used are organic in origin and are not per-
sistent in the aquatic environment. Rarely do they accumulate in animals, and there is little evi-
dence of biomagnification—in contrast to many insecticides. Occasionally continuous use of copper
sulfate has resulted in the accumulation of copper in aquatic sediments, with deleterious effects on
the bottom-living aquatic fauna.
Changes in the aquatic environment do occur, and some injury to nontarget organisms results
from the use of herbicides. This injury is almost always due to secondary effects (modification of
the habitat) or to anaerobiosis after the death of large masses of aquatic vegetation. At the same
time we frequently observe similar occurrences arising spontaneously from natural conditions in
certain bodies of water. 'The question of whether or not to restrict the use of aquatic herbicides
rises with increasing frequency. Although most opinions are based on a sincere regard for the wel-
fare of the aquatic environment, they are too often expressed without knowledge or consideration
of the consequences. To begin with, there is little doubt that aquatic vegetation will become in-
creasingly troublesome. This is due to the increasing demands made on available water resources,
the multiple uses of water, and the increasing burden of nutrients being supplied to natural waters.
Many uses of water are now dependent on some form of aquatic vegetation management and will
become more so in the future.
Irrigated agriculture would suffer a severe blow if denied the use of herbicides. Even with the
use of herbicides, operation costs have risen steadily and would increase sharply if irrigation oper-
ators were forced to return to mechanical methods. Many farmers could survive only if the prices
of farm commodities were proportionately.increased. A recent Bureau of Reclamation decision
resulted in a return to mechanical control methods on the Fort Hall Indian Irrigation Project in
Idaho. The annual cost of weed control on this project will rise from $12,000 to $134,000 (USDI,
1972). In addition, many farmers obtained insufficient water to mature crops after the change to
mechanical control, and costs for removing silt from sprinkling equipment were as great as $4000
per farmer. Other difficulties and costs involved the maintenance and repair of silt-damaged pumps,
clogged pipes and screens, choked headgates, etc. The irrigation season would be drastically short-
ened without chemicals for weed control. Estimates have shown that, without the use of herbi-
cides, farmers on irrigated land in the West would be out of water by July 15 of any growing
season.
If federal and state agencies were denied the use of herbicides, navigation on many of the
southern streams would very likely cease within 2 years.
Recreation and property values would be restricted and depressed due to the reduction in
water quality. Many important deleterious effects that would follow restrictions on the use of
aquatic herbicides could be listed. However, any activity requiring open water and freedom from
masses of aquatic vegetation would be adversely affected.
In the absence of aquatic herbicides, the demands for usable water of good quality would very
likely create increased interest in the fields of mechanical harvesting and biological control
methods. The first, though limited in practical application to many waters, can be accomplished,
but at much greater expense. The development of biological controls is a slow process; present
opinion is that, although biological control is desirable and helpful, by itself it will not solve many
of the aquatic weed problems.
Overall, the effect of restrictions on herbicide use would be as follows:
1. To reduce the quantity of acceptable water available for various activities and conse-
quently more intensive use of these
2. To increase the need and demand for mechanical control regardless of cost
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3. To increase the expense of vegetation management
4. To increase the cost of living through more costly food and recreation
5. To reduce the level of acceptability of water quality and opportunities for recreational
and other uses of water
On the positive side we can assume some reduction in the level of water pollution from the use
of herbicidal chemicals. If some chemical operations do in fact reduce the quality of fishing, some
improvement should be expected. The hazard of unknown and long-term deleterious effects of
aquatic herbicide use on the environment would be eliminated along with attendant residues.
Training Requirements for Users.—Because the aquatic environment is complex and misuse of
chemicals could be far reaching, users of aquatic herbicides should have adequate training and
experience. Many states are now employing a permit system of use. Issuance of permits probably
will be done locally by a professional agriculturist, fish and game warden, or other employee who
has training and experience in the field. Users in public waters should be trained, professional,
custom applicators or qualified state employees. Users of aquatic herbicides in private waters would
require no specific training or experience. However, in these instances, the trained individual issuing
the permit should ensure that the proposed use is safe and reasonable and that the user is aware of
and will follow labeling and other restrictions.
REFERENCES
Anonymous, 1962. Sport Fishing—Today and Tomorrow, Outdoor Recreation Resources Review
Commission Study Report 7.
Anonymous, 1968. Water Quality Criteria, Report of the National Technical Advisory Committee
to the Secretary of the Interior, pp. 158-159.
Anonymous, 1972. National Survey of Fishing and Hunting, 1970, Bureau of Sport Fisheries and
Wildlife, Resources Publication No. 95.
Avault, J. W., Smitherman, R. O., and Shell, E. W., 1966. In FAO World Symposium on Warm-Water
Pond Fish Culture, Rome, 1966, FAO Fisheries Report No. 44, pp. 109-122.
Averitt, W. K., 1967. Report on the Persistence of 2,4-Dichlorophenoxyacetic Acid and Its Deriva-
tives in Surface Waters When Used to Control Aquatic Vegetation, University of Southwestern
Louisiana, Lafayette (unpublished).
Bailey, B., 1971. A Review of Arkansas' Grass Carp Project, Weed Science Society of America, St.
Louis, Mo. (mimeographed).
Battelle-Northwest Laboratories, 1970. Degradation and Depletion of Herbicides in Drainage
Waters and Accumulation of Residues in Crops Irrigated with Treated Water, unpublished
report.
Battelle-Columbus Laboratories, 1971. Water Quality Criteria Data Book, Vol. 3, Effects of Chemi-
cals on Aquatic Life, Environmental Protection Agency Project No. 18050 GWV. 50/71.
Bruns, V. F., 1954. Weeds, 3, 359.
Bruns, V. F., 1957. Weeds, 3, 250.
Bruns, V. F., and Clore, W. J., 1958. Weeds, 6, 187.
Bruns, V. F., and Dawson, J. H., 1959. Weeds, 7, 333.
Cochrane, D. R., Pope, J. D., Jr., Nicholson, H. P., and Bailey, G. W., 1967. Water Resources Res.,
3, 517.
Condon, P. A., 1968. The Toxicity of Herbicides to Mammals, Aquatic Life, Soil Microorganisms,
Beneficial Insects and Cultivated Plants, 1950-65. A list of selected references. National Agri-
cultural Library, U.S. Department of Agriculture, Library List No. 87.
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Dean, J. L., 1969. Biology of the Crayfish Orconectes causeyi and Its Use for Control of Aquatic
Weeds in Trout Lakes, Bureau of Sport Fisheries and Wildlife Technical Paper No. 24.
DeVaney, T. E., 1968. Chemical Vegetation Control Manual for Fish and Wildlife Management
Programs, Bureau of Sport Fisheries and Wildlife Publication No. 48.
Frank, P. A., and Comes, R. D., 1967. Weeds, 15, 210.
Frank, P. A., and Demint, R. J., 1969/1970. Annual Report of Weed Investigations in Aquatic and
Noncrop Areas, U.S. Department of Agriculture, Agricultural Research Service, Crops Re-
search Division (unpublished).
Frank, P. A., Demint, R. J., and Comes, R. D., 1970. Weed Sci., 18, 687.
Frank, P. A., and Demint, R. J., 1971. Annual Report of Weed Investigations in Aquatic and Non-
crop Areas, U.S. Department of Agriculture, Agricultural Research Service, Crops Research
Division (unpublished).
Grant, B. F., and Schoettger, R. A., 1972. Proc. Tech. Sessions 18th Annual Meeting of the Insti-
tute of Environmental Sciences, pp. 245-250.
Grzenda, A. R., Nicholson, H. P., and Cox, W. S., 1966. J. Am. Waterworks Assoc., 58, 326.
Heath, R. F., Spann, J. W., Hill, E. F., and Kreitzer, J. F., 1972. Comparative Dietary Toxicities of
Pesticides to Birds, Bureau of Sport Fisheries and Wildlife Special Scientific Report—Wildlife
No. 152.
Holm, L. F., Weldon, L. W., and Blackburn, R. D., 1969. Science, 166, 699.
Hutt, A., 1971. Florida Wildlife, 24, 16.
Lawrence, J. M., and Hollingsworth, E. B., 1969. Supplement to Aquatic Herbicide Data, Supple-
ment to Agricultural Handbook No. 231, U.S. Department of Agriculture, Agricultural Re-
search Service.
Maddox, D. M., Andres, L. A., Hennessy, R. D., Blackburn, R. D., and Spencer, N. R., 1971. Bio-
science, 21, 985.
Menzie, C. M., 1969. Metabolism of Pesticides, Bureau of Sport Fisheries and Wildlife Special Sci-
entific Report—Wildlife No. 127.
Michewicz, J. E., Sutton, D. L., and Blackburn, R. D., 1972. Weed Sci., 20, 106.
Pelzman, R. J., 1971. The Grass Carp, the Resource Agency of California, Department of Fish and
Game, Inland Fisheries Administrative Report No. 71-14.
Pimentel, D., 1971. Ecological Effects of Pesticides on Nontarget Species, Executive Office of the
President, Office of Science and Technology.
Sills, J. B., 1970. Prog. Fish-Cult, 32, 158.
Sneed, K. E., 1971. Amer. Fish Farm. & World Aquacult. News, 2, 6.
Stanford Research Institute—Final Report, 1970. Investigations of Herbicides in Water and Crops
Irrigated with Water Containing Herbicides (unpublished).
Stevenson, J. H., 1965. Prog. Fish-Cult., 27, 203.
Stickle, L. F., 1968. Organochlorine Pesticides in the Environment, Bureau of Sport Fisheries and
Wildlife Special Scientific Report-Wildlife No. 119.
Timmons, F. L., 1960. Weed Control in Western Irrigation and Drainage Systems. Losses Caused
by Weeds, Costs and Benefits of Weed Control. ARS 34-14, Joint Report, Agricultural Re-
search Service, U.S. Department of Agriculture, and Bureau of Reclamation, Washington, D.C.
Toth, S. J., and Riemer, D. N., 1968. Weeds Trees Turf, 7, 14.
Tucker, R. K., and Crabtree, D. G., 1970. Handbook of Toxicity of Pesticides to Wildlife, Bureau
of Sport Fisheries and Wildlife, Resource Publication No. 84.
U.S. Army Corps of Engineers, 1965. Expanded Project for Aquatic Plant Control, House Document
251, 89th Congress, 1st Session.
U.S. Army Corps of Engineers, Jacksonville, Florida, District, May 24, 1972. "Hyacinth Spraying
Program in St. Johns River Expanded," news release.
U.S. Congress, House of Representatives, 1957. Waterhyacinth Obstructions in the Waters of the
Gulf and South Atlantic States, House Document No. 37, 85th Congress, 1st Session, p. 11.
U.S. Department of Agriculture, 1959, 1964. Agricultural Census.
135
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U.S. Department of Agriculture, 1963. Chemical Control of Submersed Waterweeds in Western
Irrigation and Drainage Systems, Joint Report of the Agricultural Research Service and Bureau
of Reclamation, Washington, B.C., ARS 34-57.
U.S. Department of Agriculture, 1965. Losses in Agriculture, Agricultural Handbook No. 291, pp.
103, 117.
U.S. Department of Agriculture, 1969. Suggested Guide for Weed Control, Agricultural Handbook
No. 332.
U.S. Department of Agriculture, 1972. Extent and Cost of Weed Control with Herbicides and an
Evaluation of Important Weeds, 1968. Publication ARS-H-1.
U.S. Department of the Interior, June 15, 1972. Decision on the Appeal of Fort Hall Water Users
Association, Office of Hearings and Appeals, Salt Lake City, Utah.
Walker, C. R., 1964a. Water and Sewage Works, 3, 113; 4, 173.
Walker, C. R., 1964b. Proc. Eur. Weed Res. Coun. 3rd Intern. Symposium on Aquatic Weeds, pp.
119-127.
Walker, C. R., 1969. In Fish and Chemicals, A Symposium on Registration and Clearance of Chemi-
cals for Fish Culture and Fishery Management, 99th Annual Meeting of the American Fisheries
Society, pp. 1-139.
Walker, C. R., 1971. Hyacinth ControlJ,, 9, 5.
Walker, C. R., 1972. Proc. Tech. Sessions 18th Annual Meeting of the Institute of Environmental
Sciences, pp. 235-237.
Yeo, R. R., 1970. Weed Sci., 18, 282.
Yeo, R. R., and Fisher, T. W., 1970. First Intern. FAO Conf. Weed Control, Working Paper No. 37,
pp. 450-463.
CROPS
Introduction
Man's survival and standard of living depend on his manipulation of the environment to pro-
duce an ecological situation favorable to the growth of crops. Weed control is one of the major
environmental manipulations necessary for the efficient and economical production of crops (NAS,
1968, p. 254).
Weed control in crops is an extremely broad and complex problem. Target weed species in-
clude annuals, biennials, and perennials with large differences in rooting depth, heights, spreading
habit, etc. Also included is a wide range of plant types such as ferns and thousands of different
angiosperms, both monocotyledons and dicotyledons. Because crops are grown under such a vari-
ety of conditions, weed species in those crops also vary widely. They can include both terrestrial
plants and, in the case of rice, aquatic plants.
Weeds growing in cropland interfere with production of the desired crop. This can result from
competition for light, moisture, and nutrients. In some cases, it may involve allelopathy, that is,
growth inhibition caused by chemicals produced by the weeds. These effects lead to a reduction in
crop yields. Weeds can also reduce the quality and marketability of crops. For example, wild garlic
in wheat will impart an unpleasant flavor to the flour, and downy brome in alfalfa will reduce the
value of the hay produced. Weeds can interfere with harvest operations. Green weeds in grain crops
may cause heating and spoilage of the grains during storage. Weeds can harbor diseases, insects, and
rodents that attack crop plants.
Hundreds of commercial crops, such as solid-seeded small grains, row crops, and orchards, are
grown in the United States. Some crops are annuals, others are perennials. Furthermore, environ-
mental conditions and weed problems differ markedly across the country even within the same crop.
These wide differences obviously necessitate the use of different weed control practices, including
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herbicides. One particular herbicide may work efficiently in a specific crop in one state but not in
another. Also, continuous use of the same herbicide in a given location results in a buildup of resistant
species or types (Ryan, 1970). These factors have led to a demand for a wide array of herbicides.
Losses due to weeds can be severe. In the United States, rice yields were reduced by an esti-
mated 17 percent each year from 1950 to 1961, resulting in an annual loss of $46 per acre (USDA,
1965). Uncontrolled weeds have reduced corn yields by over 90 percent (Behrens and Lee, 1966).
Similarly, weeds in sugar beets have reduced yields by 90 percent or more (Dawson, 1965; Zimdahl
and Fertig, 1967). Many examples could be cited.
Growers have benefited greatly from the introduction of new methods of weed control, includ-
ing herbicides. These benefits are largely in the form of increased yields and reduced costs of pro-
duction. From 1961 to 1969 rice yields increased approximately by 900 Ib/acre, representing an
approximate value of $90,000,000 for 1969 alone (USDA, 1973). A significant portion of that can
be attributed to improved weed-control measures, through the increased use of herbicides. During
the last decade the amount of hoe labor in cotton production was reduced from 48 to 13 man-hours
per acre in certain areas of the United States by the use of herbicides. The cost of labor for weeding
strawberries has decreased from as much as $200 to as little as $16 per acre where selective herbi-
cides are used in combination with tillage and cultivation (NAS, 1968, p. 255). Benefits from using
herbicides may last more than 1 year. One study (Dotzenko et al., 1969) has shown that chemical
weed control reduced the population of weeds compared to mechanical cultivation. This would re-
sult in fewer weed seeds in subsequent years.
Although there has been a turnover in the herbicides available for use in specific crop situations,
there is an increasing fear among farmers that there will eventually be a loss of usable herbicides for
a crop situation for which there is no effective alternative. Research workers in North Dakota
(Nalewaja, 1971) estimate that if the use of 2,4-D and MCPA were discontinued for wild mustard
control in cereal grains and flax, an annual economic loss of $175 million would be sustained.
These herbicides are the only feasible method now available for controlling wild mustard in these
crops. During the last 20 years, the use of 2,4-D to control weeds in an accumulated 460 million
acres of wheat increased the yield by about 2 billion bushels, valued at $3.25 billion.
In 1971, (Delvo, 1971) conducted a study to evaluate the economic impact of three herbicide-
use restrictions on typical cash-grain farms in 17 counties in Nebraska. He considered both herbicidal
and nonherbicidal control procedures. The return to the operator for labor and management ranged
from $1900 on a 400-acre dryland farm to $7700 on a 640-acre irrigated farm when preemergence
herbicide treatments and cultivation were used to control weeds. Economic returns dropped to $550
and $1700 for these two farm situations when only preemergence herbicide treatments were used,
and were negative when only cultivation was used to control the weeds. This points out the vulnera-
bility of our present farm units if only one of their major production tools (herbicides) is restricted.
Questions about the environmental impact of herbicides often revolve around their persistence
in the soil. It is frequently thought that any persistence in itself is detrimental-to the environment.
This is not necessarily true. Under some situations the persistence of a herbicide used on agricultural
cropland can actually result in decreased potential environmental damage. There are occasions when
a short-term or short-persistence herbicide is most advantageous and would result in less potential
environmental contamination. There are other situations when the use of a longer persisting herbi-
cide would result in less risk for environmental contamination. To produce a crop economically the
farmer must be able to grow the crop without weeds in the early part of the season to prevent com-
petition, and without weeds in the late part of the season to harvest a high-quality crop economically.
If the environmental conditions are such that there is a potential for continual weed germination and
development through the season, the use of a persistent herbicide that would last in the field as long
as the crop could provide the most economical and most environmentally safe situation. In such a
situation only one herbicide would be used during the growing season instead of several. If such a
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persistent herbicide could not be used, it might be necessary to use a diversity of herbicides at several
application times, with resulting greater potential for environmental contamination with each appli-
cation.
The 1967-1968 market basket survey conducted by the Food and Drug Administration revealed
a total herbicide intake of the herbicides monitored of 0.00006 mg/kg of body weight per day. Thus
it would take 670 years for a 150-pound person to consume 1 gram of herbicides from his food
(Corneliussen, 1968; Duggan and Lipscomb, 1968). The average daily intake of herbicide residues
dropped from 0.00006 mg/kg of body weight per day in 1968 to 0.000008 in 1970—a drop of 86
percent (Duggan and Corneliussen, 1972). Since man is at the end of the food chain, biomagnifica-
tion of herbicide residues in food does not appear to be a problem. Soil, crop, water, sediments,
wildlife, and air samplings for herbicide residues rarely show significant amounts. This is probably
because herbicides are usually applied only once a year and most herbicides are short-persistence
pesticides. Herbicides have a built in warning system in that any accumulation in soils would be
visually evident because of their phytotoxic effects on susceptible plants.
Organic herbicides have not accumulated in the environment (Sheets and Kaufman, 1970).
Their persistence in soils and in plants is relatively short. They are eliminated from the bodies of
animals in a short time as has been shown in extensive data developed for the registration of herbi-
cides. There have been few problems with wildlife and other species resulting directly from the use
of herbicides. The dominant effect of the use of herbicides is to alter the botanical composition of
an area; a secondary impact may occur as a result. Problems with the persistence of herbicides in
soils as reported in USDA, 1972, relates primarily to damage to susceptible crops planted the year
following the herbicide application.
Herbicides can be expected to have a significant social impact. The requirement for hand labor
has been reduced dramatically in many crops, such as sugar beets, peppermint, and onions. Although
this could influence unemployment levels in some cases, labor available for hand weeding in those
crops is in fact becoming scarce and very expensive. Reduced requirements for hand weeding may
allow family members to have more time for more productive work activities. Of course, a major
social effect of herbicide use has been the continued production of lower cost and higher quality
food products for the American consumer.
The degree of weed control required for optimum economic return varies with the crop. In a
few cases nearly complete weed control is required; for example, seed crops for certification must
have few or no weeds whatsoever. This may require many methods in addition to herbicides, includ-
ing hand-rogueing. In most crops, however, the additional cost required to control 100 percent of
the weeds is seldom justified economically.
Minor Acreage Crops
Many vegetable, fruit, and agronomic crops are grown on limited acreages in the United States.
The Agricultural Handbook (USDA, 1972) suggests controls for one or more weeds in 82 crops, 43
of which are vegetables and 14 of which are agronomic crops. In addition, suggestions are made for
weed control in deciduous tree fruit and nut crops, small fruits (berries and grapes), citrus and sub-
tropical fruits and nuts, and ornamental plantings. Weeds in these crops can cause serious reductions
in yield and quality, with increased costs of production. To the individual grower the weed problems
in these crops are equal in importance to those in major crops. While many of these crops may be
grown on rather large acreages in specific localities, their production, both in terms of volume and
from an economic standpoint, may render them as minor crops or minor uses.
The principles, practices, and need for weed control that apply to "major acreage crops" are
generally applicable to "minor acreage crops." Herbicides generally have not been developed specifi-
cally for use on minor crops. Due to the cost of development, most chemical companies have felt
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that they cannot afford to produce a herbicide for the limited market involved in minor crops. His-
torically, a company that had acquired a label approval for a herbicide on a major crop could, at
limited cost, extend the label to include other crops that had similar weed problems. As a result,
growers have been able to use herbicides that were primarily developed for other crops and other
cropping situations, even though the herbicides had not been developed specifically for their needs.
With the current increase in total registration requirements, this is becoming more difficult. Because
of the expensive tests required to obtain label approval for each crop, fewer herbicides will be avail-
able to the producer of minor crops, even though the crops may be valuable to a particular segment
of our economy or may produce a specific type of food preferred by a portion of the population.
Growers of minor crops need to have the same alternatives available to them as growers of
major crops. They need to be able to rotate herbicides and to integrate them into a total manage-
ment procedure, just as other farmers do, to produce a crop profitably. Some viable procedure must
be developed whereby the growers of minor crops may be assured of the continued development of
improved herbicides needed in their management programs.
The term "minor crops" has been misleading. A newer term—"minor uses"—more clearly defines
the problem. Now that registrations must be for specific weed-crop situations, a particular use where
the volume of herbicide does not justify the cost of registration should be considered a minor use.
This is true whether the weed-crop situation is in cotton (a large-volume crop) or watercress (a small-
volume crop). All of the crops discussed in this report can be minor depending on the extent of the
pest infestation.
The problem of registration for minor uses is further complicated and intensified by the expira-
tion of patent protection, which lowers economic incentive for additional market development.
There are a number of important herbicides for which patent protection has, or soon will, run out.
Liability is another complicating factor since civil suit claims resulting from crop or ornamental dam-
age can exceed profits from the sale of a small volume of herbicide.
References
Behrens, R., and Lee, O. C., 1966. In Advances in Corn Production, W. Pierre, S. Aldrich, and W.
Martin, eds., Iowa State University Press, Ames, Iowa, pp. 331-352.
Corneliussen, P. E., 1968. Pesticides Monit. J., 2, 140.
Dawson, J. H., 1965. Weeds, 13, 245.
Delvo, H. W., 1971. Proc. Northcentral Weed Control Conf., 26, 24.
Dotzenko, A. D., Ozkan, M., and Storer, K. R., 1969. Agron. J., 61, 34.
Duggan, R. E., and Lipscomb, G. Q. 1969. Pesticides Monit. J., 2, 153.
Duggan, R. E., and Corneliussen, P. E., 1972. Pesticides Monit. J., 4, pp. 337-339.
Nalewaja, J. D., Mitich, L. W., and Dexter, A., 1971. Farm Res., North Dakota Agric. Exp. Station
28, 25.
National Academy of Sciences, 1968. Weed Control, Publication 1597.
Ryan, G. F., 1970. Weed ScL, 18, 614.
Sheets, T. J. and Kaufman, D. D., 1970. FAO International Conf. on Weed Control, pp. 513-538.
Smith, R. J., Jr., 1967. Asian-Pacific Weed Control Interchange Proc., 1, 67.
U.S. Department of Agriculture, 1965. Losses in Agriculture, Agricultural Handbook No. 291.
U.S. Department of Agriculture, 1972. Suggested Guide for Weed Control, Agricultural Handbook
No. 447.
U.S. Department of Agriculture, 1972. Extent and Cost of Weed Control with Herbicides and an
Evaluation of Important Weeds. ARS-H-I. pp.227.
U.S. Department of Agriculture, 1973. Agricultural Statistics, U.S. Government Printing Office,
Washington, D.C.
Zimdahl, R. L., and Fertig, S. N., 1967. Weeds, 15, 336.
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Row Crops
Principles, Practices, and Need for Weed Control.—In a nondramatic but very real way our sur-
vival and standard of living depend on successful crop production. Weed control is part of the more
general problem of environmental manipulation, and thus can be considered in terms of ecological
relationships. Such vegetation management consists of fostering beneficial and suppressing undesira-
ble (inefficient or uneconomical) vegetation.
The modern system of producing food tends toward a system of monoculture. Although we
attempt to grow row crops as monocultures, what we actually achieve are communities composed
of crop plants and weeds. No one plant species, crop or otherwise, can fully exploit the resources
of an agricultural habitat. In cropland and other disturbed areas numerous ecological niches are
initially unfulfilled, creating enormous pressures for invasion by an aggressive species. The invasion
is rarely entirely preventable, but it can usually be arrested in its early stages. Good husbandry
seeks to maintain environmental conditions most favorable to the crop and least favorable to the
weeds. This reduces the kind and number of ecological niches available for invasion by aggressive
species. Economic demands in agriculture have forced farmers into greater specialization because
they need to raise a crop with a higher net return per acre, and there are fewer machinery require-
ments in producing one crop rather than many. That such a system is feasible is shown by the
hundreds of years of monoculture in Hawaii or many parts of the Mediterranean world. However,
in such a situation greater care is needed to stay ahead of problems with pests and nutrient
deficiencies.
Of the several factors that limit row-crop production, the control of weeds is one of the great-
est. Only recently has research across the country produced data indicating that losses due to weeds
were far more damaging than had been suspected. In the United States the number of weed species
that commonly infest major crops is approximately 25 for peanuts, 30 for soybeans, 20 for corn, 15
for cotton, 30 for rice, 15 for potatoes, 40 for vegetable crops, and 50 for orchard crops. The scope
of weed-control operations in field and horticultural crops is enormous. Between 1951 and 1960
American farmers spent more than $2.5 billion annually to control weeds. Although nonchemical
weed-control methods are still the most widely used practices in crop production, improved herbi-
cide technology has greatly increased crop-production efficiency. In recent years this technology,
combined with efficient cultural practices, has resulted in an enormous reduction in the man-hours
required to produce crops.
Losses.—Weeds cause damage in many ways. They may reduce crop yields and impair livestock
production. They also increase production costs in growing and harvesting a crop and may impair
the quality of agricultural products by contaminating them with noxious odors, seeds, or debris.
Weeds are important in ecological or integrated pest-control programs because they may serve as
important reservoirs of insect pests and their parasites and predators, as well as plant diseases and
nematodes.
There is no reliable worldwide study, but it is evident that losses caused by weeds exceed the
losses from any other category of agricultural pest. Losses due to reduced crop yield and quality
and to the cost of weed control amount to 10 to 15 percent of the total value of agricultural and
forest products. A few specific examples of losses due to weeds follow. Data in Alabama (Buchanan
and Burns, 1970) show that mixed populations of annual grass weeds and broadleaf weeds could re-
duce yields by approximately 60 percent. When weeds were not removed until cotton reached the
squaring stage, the growth pattern of the cotton was altered, maturity was delayed, and yields were
reduced. In other studies maximum yields of cotton were produced when the crop was kept free
of annual grasses and broadleaf weeds for approximately 8 weeks after emergence. However, even
under such situations there is a concern for the presence of weeds in the harvested crop. Several
investigators have noted that weed control by hand hoeing during early cotton growth results in
lower yields than those obtained from plots treated with herbicides (Holstun, 1963 and McWhorter
and Holstun, 1957). In addition, the quality of harvested lint cotton must be considered, because
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one large crabgrass plant per 6 meters of row is sufficient to reduce the grade of mechanically picked
cotton (Garner et al, 1958).
Shadbolt and Holm (1956) published data that can be used to estimate potential weed losses in
vegetable crops. The data show that tremendous yield losses can occur when only a small number
of weeds are left in a normal population during the early stages of crop growth. A weed stand only
15 percent of normal reduced carrot yields by 39 percent and onion yields by 48 percent; 30 per-
cent of normal weed stand reduced the yields by 47 and 68 percent, respectively; and 50 percent of
normal weed stand reduced the yields by 62 and 76 percent, respectively. In vegetable crops, weeds
often reduce fruit set and fruit size. Fruit quality, including flavor, color, and texture, is also lowered.
Maturation is irregular and harvesting is difficult when weeds are present. Danielson (1970) reportee
that annual losses due to weeds in plantings of vegetable legumes may be estimated at more than
$110 million.
Some classic studies in the Corn Belt by Knake and others (Knake and Slife 1962, 1965,1969)
indicated that one foxtail weed plant per foot of soybean row reduced yields by 2 bushels per acre,
with increasing stands causing greater yield decreases. Wilson and Cole (1966) found that morning-
glory reduced soybean yields, increased lodging, and increased harvesting problems.
Dawson (1965) reported that unchecked weed competition can eliminate sugar beets as an eco-
nomic crop. Yield reduction of 94 percent due to weeds has been recorded under irrigated condi-
tions. In Colorado, kochia or lambsquarter reduced sugar beet yields by more than 94 percent
(Weatherspoon and Schweizer, 1969). Similar results have been reported in Wyoming and New York.
These reductions indicate complete crop failure, since the smaller sugar beets could not be harvested
on a practical basis because of the dense stand of weeds. The loss in sugar beet yield from weeds thai,
escape the thinning operation or emerge after thinning can be costly. For example, Brickey (1965),
reported that in California one weed per six sugar beet plants or 17 weeds per 100 feet of row re-
sulted in yield reductions of 2.9 tons per acre.
Principles.—A basic principle of plant competition and weed control is that the first plant to
occupy an area has an advantage over all later arrivals. This principle is of foremost consideration in
practical weed control where cropping practices are always directed to the establishment of the crop
ahead of the weed. Weeds that emerge after the crop is well established may not pose a serious
problem, assuming that no ecological niches are exposed too long. In addition, competition
between crops and weeds is usually most severe when the competing plants are most alike in vegeta-
tive habitats and demand on resources.
All crops grown on a farm are subject to weed competition. Most weed-control practices and
techniques exploit biological differences between the crop and the weed that are accomplished by
manipulating the shared habitat. Any attempt to put the crop in a dominant competitive position
in the crop-weed association depends on the differential response of crop and weed to some factor
of the habitat that can be modified or manipulated with predictable results. This basic concept
underlies effective weed-control practices. However, the choice of methods and techniques of agri-
cultural weed control may vary with the region, the crop, the nature of the weed, and the level of
agricultural mechanization.
The degree of competition between weed and crop varies with the crop species. The weed prob-
lem for soybeans is different from that for corn, because weeds can shade soybeans but are less likely
to shade corn once the plants become established. Although the shading effects of weeds on soybeans
are most apparent when the weeds overtop the crop, recent studies show that velvetleaf plants sig-
nificantly reduced growth and yield when placed on one side of the soybean rows even though they
never grew taller than the bean (Burnside and Coleville, 1964). Side shading has been shown to be a
significant factor in yield reduction. With vegetable crops, such as onions, beets, and carrots, shading
by weeds can exert an almost overriding effect in many situations.
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Another basic principle of row-crop weed control is to use control methods that are directed at
weed survival mechanisms in the soil wherever possible. For annual weeds the objective is to pre-
vent seed production and deplete plant food reserves. For perennials the destruction of under-
ground vegetative organs is sought. Many soil-tillage and seedbed-preparation practices may
minimize the competitive effects of weeds and crops. However, they may be largely ineffective in
dealing with the basic survival mechanisms of a weed species.
There has recently been much publicity about the so-called green revolution with the new vari-
eties of crops being produced. One thing frequently ignored is that, if these new miracle varieties
are grown in the environment of the old varieties they are replacing, they often produce very little
more yield. The most important feature of these new varieties is their capability to utilize effi-
ciently fertilizers and irrigation and to produce well in dense plant populations. For this to occur
the new varieties must be kept free of weeds that would otherwise use the fertilizer and water and
perhaps smother the crop.
Methods of Control.—In contrast to other agricultural disciplines and their techniques, no
method of weed control has ever been totally discarded. The oldest methods still have their place
and are often combined with new procedures. Unlike insect and disease pests, weeds are relatively
steady components of the agricultural environment and do not appear as periodic plagues exciting
public clamor and support for action. There is a major basic difference between herbicides and
other pesticides in their function as part of modern agriculture. Insecticides and fungicides protect
crops and stored products from the direct attack of various pests. Herbicides not only protect
growing crops from the heavily detrimental effects of unwanted plants but also offer the promise of
weed-free crop production. This would make it possible to completely change the basic agricultural
practices that have been carried on for centuries. Because weeds have always been associated with
the production of crops and because the damage they cause is less obvious than that caused by
other pests, there has often been a lack of a true appreciation of how damaging weeds are to effi-
cient production. Once it is possible to create a weed-free environment cheaply and efficiently with
modern agricultural procedures, many of the historical agricultural practices can be changed.
Nonchemical Weed Control.—The weed-control methods used in row crops are classed as
preventive, biological, habitat management, physical, or chemical. Preventive weed control encom-
passes all measures taken to forestall the introduction and spread of weeds. Preventive measures
may reduce infestation, but no preventive program can be expected to eliminate the numerous
species of weeds found on any given land area. Because of the high reproductive capacity, special
dissemination characteristics, dormancy, and high seed viability of weeds, preventive weed control is
difficult if weeds are in, or adjacent to, the farmer's field. The effectiveness of a preventive program
varies with the weed species. For example, because weeds like Canada thistle and kochia are readily
spread by the wind, it is unlikely that preventive practices will effectively control them. Prevention of
weed seed production, good farm-management practices (clean, vigorous, and well-adapted seeds),
optimal rate and placement of fertilizer, timely tillage, crop rotation, use of clean farm equipment,
animal management, and proper weed control on irrigation and drainage waters are some of the
preventive weed-control methods currently being used.
The use of natural enemies to reduce the population of a plant species is known as biological
control. When suitable and effective agents are available, this method is cheap and relatively perma-
nent. The objective in biological control is never eradication; it is reduction of a weed plant density
to economically acceptable levels. Biological control of row-crop weeds has been viewed conserva-
tively for two reasons: (1) the possibility that it may not be as effective as other methods in obtain-
ing an adequate degree of weed control and (2) conflict in the classification of a given plant as a
weed, particularly since introduced agents may readily move from areas where the plant is a weed to
areas where it is considered of value. Because of the risk to other plants, insects that are unspecial-
ized feeders are not used in plant biological control. Many weeds are close relatives of crop species;
examples are wild oats and cultivated oats, Sudan grass grown as forage and johnsongrass, and
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potatoes and tomatoes and the troublesome perennial weed horsenettle. Thus we are concerned
with a relation where the introduced enemy is food limited and the weed host is enemy limited in a
typical host-parasite interaction. By the very nature of the controlling mechanism the absolute
impact of an enemy's action is automatically lessened as the density of the host declines. Also,
many weeds are erratic in their occurrence in time and space, and the need for control may be
urgent.
Although these factors lessen the likelihood of obtaining success with biological control, they
do not preclude the possibility. The greatest disadvantage is that biological control is by its very
nature a very selective and specific process. It cannot be used to control a complex of many weeds.
It has striking utility where a single aggressive weed is devastatingly troublesome. However, the
current usage of herbicides has shown that, if one specific weed species is eliminated or controlled
in a given crop, other weed species are likely to invade and become the dominant weed problem.
Thus any controlling factor that concentrates on one specific species is not likely to be the long-
term solution to controlling weeds in any crop.
Some weed-control techniques manipulate the environment to reduce or eliminate competition
by weeds or prevent their introduction or spread while the desired use of the environment is main-
tained. This procedure is known as habitat management. Weed species that may infest any given area
are so numerous and diverse that any one control method is rarely satisfactory. Often, however, the
interaction between weeds and their environment is delicate, and a change in the timing of events or
condition of the environment may have an effect on the kind, stand, and vigor of weeds. For exam-
ple, in the southern great plains region, winter small grains planted late in the fall do not have prob-
lems with cheat, but yields may be lower and cattle cannot fall graze on the forage. As crops are ro-
tated, varying conditions of soil manipulation and planting procedures, tillage, fallow methods,
mulching practices, and fertilizing practices may be used. Manipulation of water supply as it varies
for different crops in the form of irrigation, flooding, or draining may help to control weeds as a
habitat-management practice. Such variation makes it difficult for a single weed species to become
a major problem in a specific area.
Physical methods are the oldest known procedure for controlling weeds and are still dominant
in modern weed control. However, they cannot by themselves provide the degree of weed control
needed in modern agriculture. Seed dormancy, the presence of various perennial underground stor-
age organs, the production of literally thousands of seeds per weed plant, and the wide dissemination
of seed by various means all combine to produce conditions under which many species cannot be
completely controlled by physical methods.
Various physical control methods can be used, including tillage (physically altering the weed
relationship with the soil), mowing and cutting, flooding or draining, the use of heat, and smother-
ing. Of these procedures, tillage is probably the most widely used.
Tillage for weed control includes all soil-disturbing procedures ranging from hand pulling or
hoeing through mechanical land preparation to machine cultivation of large acreages after the crops
have emerged. Preplanting tillage (seedbed preparation) removes germinated weed seedlings but
does not produce a significant depletion in seed reserves in the soil. Postplanting tillage (cultiva-
tion) may remove or bury weeds in the row, but it weakens crop plants through root pruning or
other injuries. In general, cultivation is of little benefit other than for weed control under many soil
conditions. However, in very heavy soils cultivation may offer benefits beyond weed control, par-
ticularly in aerating the soil and permitting greater moisture penetration. Thompson et al. (1931)
found weed control to be the main advantage derived from one cultivation of vegetable crops. Later
cultivation injured roots and actually reduced yield. Gates and Cox (1912) concluded from 125 tests
in 28 states that cultivation benefited corn only by the removal of weeds. The frequency of tillage
operations ranges from a single operation of a one-way disk and planter to repeated plowing, disking,
and harrowing before planting and repeated cultivation after planting.
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In general, tillage operations are effective primarily against seedling weeds. They are relatively
ineffective against intact seed in the soil and against perennial weed species. With most perennials
the main accomplishment is removal of the plant top without significant injury to the root storage
organ. Adverse weather conditions severely limit the usefulness of many tillage operations.
Furthermore, continued operation of heavy tillage implements over a field is very detrimental to
soil conditions; procedures that can replace heavy tillage implements have been found to increase
yield, improve soil structure, produce better soil aeration, and allow roots to permeate the upper
layers of the soil more successfully. Yarrick (1946) indicated that the near elimination of tillage was
an important innovation for the citrus industry.
The wide spacing of row crops is generally governed by the necessity of maneuvering between
the crop rows to cultivate for weed control. The traditional 40-inch corn row was determined by
the necessity of having a horse or mule walk between the rows while cultivating. With the introduc-
tion of modern weed-control methods, it is no longer necessary to maintain these spacings. Re-
search is showing that the traditional wide rows can be reduced considerably, and higher crop-plant
populations in the field can produce higher yields more economically and frequently with less need
for pest control. If conditions are such that the crop seedlings can emerge and grow faster than
competing weed seedlings, narrow-row plantings may be more productive than widely spaced rows,
which leave sufficient space for competing species.
So-called minimum-tillage procedures are coming to the fore. These permit economically suc-
cessful crop production while requiring less frequent soil disturbance for weed control. These pro-
cedures, however, must involve postplanting weed-control methods other than tillage.
Other physical control methods are generally less useful with cultivated row crops. Mowing
and cutting are effective methods for perennial forage crops but cannot generally be used in culti-
vated crops. Draining is useful in certain specific areas, but it is not an operation that is used on a
repeated basis. Flooding is used in some field crops but generally not for cultivated crops. Heat is a
practical means of controlling weeds selectively in some cultivated crops. The use of flamers to con-
trol weeds in cotton has long been an established practice. Selective flaming has also had limited use
in other crops, such as corn, soybeans, grain sorghum, and castorbeans. Weed kill is accomplished by
moving an intense flame along the base of a weed-infested crop. Selectivity requires very careful
timing and precise physical conditions, both of the soil and the crop. Flaming has definite limita-
tions, but it can be used under certain situations. In most crops weed control cannot be obtained
from flame alone; it must supplement other weed-control practices. Flaming requires propane (a
petrochemical) as a fuel source.
Chemical Weed Control.—The other major method of controlling weeds in row crops is the use
of herbicides. Herbicides can be used either to kill weeds or to inhibit their normal growth. Their
means of accomplishing this are diverse and in some instances unknown.
Research with 2,4-D after World War II established that herbicides could be effective in very
small quantities, highly selective, and systemic in action. The small quantities offered promise of
inexpensive weed control. Selectivity meant that weeds could be killed in the presence of crop
plants or seedlings. Systemic action made it possible to kill the underground parts of plants by
applying herbicides to the foliage. Although its effectiveness was dramatic, it was soon found that
2,4-D was no panacea. Tolerant broadleaf weeds and resistant grasses survived treatment and in-
creased in number. This led to the development of other herbicides in attempts to control these
various weed species and to extend the usefulness of the herbicide procedures to other crops that
may themselves be susceptible to 2,4-D. As time has passed, it has become evident that no single
herbicide is sufficient and that our weed problems constantly change.
The farmer uses herbicides because his objective is to economically grow as much of a useful
crop as possible. In modern agriculture he must attempt to channel the maximum amount of
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available resources into useful crop production of improved quality. Herbicides have played an
important role in farmers' ability to increase crop production while withstanding the present cost-
price squeeze and the decreasing farm-labor supply. In 1950, 75 man-hours were required to pro-
duce 1 acre of peanuts in Georgia; in 1969, only 15 man-hours were required. During the last 30
years the yield per acre has tripled for corn and potatoes and has approximately doubled for wheat,
peanuts, and cotton (32). At the same time, the man-hours required to produce an acre of each of
these crops decreased by 80, 36, 66, 77, and 70 percent, respectively. Chemical weed control con-
tributed dramatically to this increase in productivity per man-hour expended.
Some of the major benefits of herbicide use on farms are the following:
1. The physical burden of weed control is diminished because much of the hand labor is
eliminated.
2. Fewer people are involved in farm work where machines and herbicides are widely used;
where fewer people are required to produce food, other vocations can be pursued and the general
well-being of the entire population can be enhanced.
3. Increased productivity has resulted in efficient farm production at a lower price per unit.
Herbicides may be applied to weeds in crop rows where cultivation would be impossible. Also,
preemergence herbicide treatments provide early season weed control and prevent weed competi-
tion long before tillage methods would be used to control the weeds without crop injury. Weed
competition during the early stages of crop growth is responsible for the greatest loss in yield. Cul-
tivation often injures the crop root system as well as the foliage, and selective herbicides reduce the
need for cultivation. Herbicides also reduce the destructive effects of tillage on soil structure.
Moreover, preemergence treatments can be controlling weeds even if the farmer cannot get into the
field to cultivate due to rainfall or other adverse conditions. Chemical weeding permits simplifica-
tion of crop rotation, avoidance of soil disturbance, adjustment of row spacing to that optimum for
each crop, and economy of labor.
There are detrimental as well as beneficial effects from the use of herbicides. Possible detri-
mental effects of herbicides in cultivated crops could be summarized as (1) drift from the target
area and detrimental effects to nontarget plants, (2) persistence in soil, (3) injury to treated crops,
(4) potential persistence in air and water, (5) movement in groundwater, (6) undesirable shifts in
the weed population, (7) hazards to animals, and (8) hazards to man. The major herbicide problems
have generally been due to herbicide drift to nontarget species or persistence in soil and water.
Although herbicides are necessary for future crop production, their undesirable secondary ef-
fects cannot be ignored. As a group the organic herbicides are primarily toxic to green plants. Most
of them are not highly toxic to members of the animal kingdom (WSSA, 1974; Hayes, 1964; Hayes
and Perkle, 1966). The principal hazard in the use of herbicides is to crops or other desirable vegeta-
tion. The Governor's Scientific Advisory Panel on the use of agricultural chemicals in Texas (Adkis-
son, 1970) indicated that the "principal danger from herbicide pollution is to crops and plant life
rather than to man or wildlife. This pollution can be reduced through proper application or by the
use of mixtures of nonpersistent herbicides." Although the principal hazard is to desirable vegeta-
tion, the entire biological environment must always be considered.
Type. Herbicides can be classified as either inorganic or organic. Inorganic herbicides are not
widely used as selective herbicides in row crops. Many different types of organic herbicides are being
used, and they can be roughly classified into various chemical groupings. Herbicides within a given
chemical group may be somewhat similar in the type of weeds controlled, the type of crops in which
they are selective, and their mode of action. However, there may be wide variation in the specific
weed species that will be susceptible to any given member of a chemical family. Also, there can be a
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variation in the crops susceptible to different chemicals in the given family. Linuron, a substituted
urea herbicide, can be safely used in soybeans; fluometuron, also a substituted urea herbicide, will
kill the crop. Atrazine can be safely used in corn but will kill cotton; with prometryne, another tria-
zine herbicide, the reverse is true. Trifluralin provides excellent control of crabgrass in soybeans,
peanuts, and cotton but little or no control of morningglory or cocklebur.
Chemically there are wide differences among the various herbicide families. No specific chemi-
cal structure is universally successful as a herbicide, and no portion of a molecule can be pointed to
as the active agent. Although some major herbicide families find more use in cultivated crops than
others (e.g., the triazines, the substituted ureas, and the dinitroanilines), some members of every
chemical family are used in one or another cultivated crop.
No attempt has been made in this report to discuss specific-chemical weed-control procedures
used in dozens of row crops with more than 100 selective herbicides. A given herbicide is quite spe-
cific as to the crop it is used in, the time of use, the weed species controlled, the prevalent soil con-
ditions, and the environmental conditions before and after treatment. Recent publications by the
National Academy of Sciences (1968) and the Food and Agriculture Organization (1970) summa-
rize current herbicide procedures.
Knowledge of the environmental factors regulating herbicide performance or limiting herbicide
usage is essential to the successful control of weeds with herbicides. The risk of failure is always
present. Environmental factors appreciably modify plant growth and plant response to imposed
conditions. Thus variation in environmental factors will have a significant effect on herbicide
action. The same response might be expected time after time from a typical herbicide applied at
the same dosage rate in the same environment. In another environment the rate required for a
similar level of activity may differ by two to four orders of magnitude. Various properties of soil
and herbicide, as well as environmental factors, influence activity and persistence through their
effect on volatilization, movement in soils, microbial decomposition, adsorption to soil colloids,
plant absorption, and plant metabolism. Frequently, the limitations imposed by the environment
on the weed control obtained with a specific herbicide may be overcome by using a different herbi-
cide. Often the advantage of adding a new herbicide to the arsenal of those available is that it
covers a specific environmental or weed condition not presently adequately covered.
Most growers have come to realize that adequate and economical crop production does not
mean that all weeds must be eradicated from a field. The weed population must be reduced to a
level that is relatively noncompetitive with the crop. If given an advantage, the crop can frequently
outcompete the weeds in the same field and produce an economical yield. Some crops are more
effective in this way than others. A crop like peanuts or soybeans, which produce a dense, shading
type of growth, will prevent the emergence of many weeds once it has established a sufficiently
dense foliage. Crops like tomatoes or sorghum do not produce such dense foliage early in the
season, and thus there may be trouble with weeds later in the growing year. Thus the degree of
control needed will vary with the crop and will influence the choice of herbicide.
Although there are variations in the degree of weed control needed in various crops, the risk of
failure is always present. Unfortunately, this sometimes induces the farmer to use more herbicide
than may actually be needed. Chemical weed control in the 1940s was used in conjunction with
various other procedures strictly as an added weed-control method. If the herbicide was not suc-
cessful, the farmer could always plan to cultivate his crop until midseason. Since then the economic
situation has imposed on the farmer the need to reduce costs while increasing production, and the
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farmer has been forced to improve production procedures. These improved procedures frequently
include the use of herbicides in situations where no other weed-control procedure can be economi-
cally used. Examples of this include the narrow-row growing of sorghum in irrigated areas of the
southwest as well as the production of minimum- or zero-tillage crops in the Eastern United States.
Under these situations the failure of a herbicide treatment or the absence of alternative herbicide
treatments can readily mean complete loss of the crop. Therefore, under such situations the risk of
failure is a major consideration to the grower in establishing his herbicide program.
Although the elimination of early competition to the crop permits the plants to reach their full-
est yield, there are also hazards to a failure in weed control late in the growing season. Modern har-
vesting machinery has been developed to harvest clean crops. The presence of a heavy weed stand at
the time of harvest hinders or makes impossible the use of harvesting machinery. The presence of ex-
cessive grasses in cotton causes a discoloration of the lint that cannot be removed and therefore re-
duces the quality of the cotton. The presence of excessive pigweed in a soybean field can completely
prevent combine operation or slow it down sufficiently to drastically increase the cost of harvesting.
Often the only possible control procedure for a weed problem appearing in a maturing crop is the
use of herbicides.
Persistence. The detoxication, degradation, and disappearance of herbicides use"d in cultivated
crops vary widely among the soils and in response to differences in environmental factors. The resi-
dues of some herbicides used in cultivated crops may persist from one season to the next and injure
sensitive crops the season after application. However, this is more detrimental to the farmer grow-
ing crops on that land than to anyone else. Current research is finding herbicides that are less persist-
ent and do not have a 6- to 12-month carryover in the soil. However, some persistence is an essen-
tial feature of some herbicides. A herbicide like trifluralin, which is applied in April prior to the
planting of a cotton or peanut crop in May, must have some persistence if weeds are to be con-
trolled until the crop has developed enough to fend for itself. Frequently, a 2- to 3-month period
of persistence is optimal. The development of more and better contact herbicides can to some
degree reduce the use of persistent materials, but these compounds will never be able to completely
replace the persistent herbicides. Ideally the herbicides should control the weeds until they are no
longer a problem in the crop and then degrade.
Several years ago there was considerable concern about the potential accumulation of high con-
centrations of herbicides in the soil of cultivated crops due to repeated application of herbicides.
Evidence from many long-term experiments indicates that the accumulation of high concentrations
does not occur. Repeated annual applications at selective rates to the soil does not tend to build up
into an accumulation that will injure the crops being grown (Hill et. al., 1955; Burnside et. al., 1969;
Gunther, 1970).
Systems of Weed Control. Research has shown that agricultural crop production can be in-
creased without an increase in environmental contamination by adopting the systems approach to
weed control in cultivated crops. This is not a new concept. Weeds have always been controlled
best by a variety of practices, and man for thousands of years has employed combinations of tillage,
cropping, and environmental management in his battle against weeds. The twentieth century revo-
lution in weed technology has permitted application of the systems concept. Weeds may now be
dealt with systematically over time and space through a series of coordinated techniques that have a
greater impact than any one component by itself. Therefore, deleting any one component of the
system is much more serious than just omitting one step in a practice. The primary goal of any
weed-management system is to maintain an environment that is as selectively detrimental to weeds
as possible.
Though the successful employment of specific or combined ecological, cultural, mechanical,
biological, and herbicidal methods approaches the objective in controlling a particular weed species,
the weed complex may change as the environment changes or resistant strains become prevalent.
Fortunately, more is continually being learned about weed control, and new treatments are
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constantly being perfected. These developments serve to improve existing weed-management sys-
tems and suggest changes in approach for methods that become ineffective or obsolete.
Currently there is considerable interest in the zero- or minimum-tillage crop-production sys-
tem, and this has found expression in changes in our weed-control procedures. In such programs a
herbicide is doing more than just controlling weeds. Herbicides are also crop production tools.
They are tools without which a system of minimum tillage would not be practicable. The many
advantages of minimum-tillage procedures include major reductions in soil compaction, soil erosion
from wind and water, and production costs. Minimum tillage is one pest-control system that would
not be possible without pesticides.
Weeds compete with cultivated crops throughout the growing season. Usually no one herbi-
cide will give full-season control of most broadleaf weeds and grasses. Different species of weeds
often compete with a crop as the season progresses. Thus, to obtain full-season weed control with
or without cultivation, it is frequently necessary to use different herbicides at different times. The
grower must select herbicides best suited to the particular weed problem. This is particularly true as
only the less persistent herbicides are produced. If most of the herbicides are short-lived, the
grower may have to apply herbicides several times during the growing season to obtain full-season
weed control.
Complex systems will not control all weed species under all conditions, but the chances of fail-
ure can be greatly reduced. The complementary action of components in a weed-control system is
apparent in a study conducted of cotton (McWhorter et. al., 1956; Holstun et. al., 1960). Flame
weeding reduced hoe labor requirements by 11 hr/acre, and a preemergence herbicide reduced them
by 18 hr/acre. These individually total 29 hr/acre, but the actual reduction where both procedures
were used was 47 hr/acre. In Nebraska weeds reduced grain sorghum yields by about 33 percent
where either cultural or chemical practices were used alone for weed control. Plots that received
both herbicides and cultural weed-control practices produced 1000 Ib/acre more grain than plots re-
ceiving either control treatment alone (Burnside et al., 1964).
Alternatives. Although the common weeds of field and pasture are taxonomically diverse,
they are all nuisances. They are particularly adapted to thrive in close association with man and his
domesticated plants and animals. Hence the use of any one procedure can only rarely provide the
degree of weed control needed for economical crop production. Different alternative methods of
weed control must always be considered, and more than one alternative is needed.
Tillage or soil-disturbance operations provide acceptable alternatives to the use of herbicides
for weed control in some situations. However, as has already been shown, there are many problems
that tillage cannot solve because of environmental conditions or the characteristics of the weed
species to be controlled. Often, if the farmer planned to cultivate, it may rain enough to prevent
cultivation. By the time this occurs he may have lost his best possible alternative herbicide
treatment.
One possible alternative to the continued use of a dominant herbicide is to practice herbicide
rotation, either in conjunction with continuous cropping of a single crop species or in conjunction
with a crop-rotation procedure. At the University of Illinois F. W. Slife (data to be published in
Weed Science, 1975) has now completed 6 years of a field experiment involving rotations (or the
lack thereof) of crops and of herbicides. Continuous corn and continuous soybean plots consistently
provided better yields in plots that received either a main or a rotation herbicide as compared to
those that received only tillage for weed control. The same was true to a lesser degree of corn or
soybeans in rotations. Evaluations of weed seed in soil at the beginning of the experiment and after
6 years of treatment showed that there was a weed-seed buildup of selected species when a single
main herbicide was used each year under a continuous corn rotation. The same was true even to a
greater degree under the nonchemical treatments. With the rotation of herbicides (using a different
herbicide treatment each year in the corn crop), the weed-seed population in the soil was drastically
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reduced. With continuous soybeans the weed-seed population of the soil dropped with both the
main herbicides and the rotation herbicide procedures but increased threefold under the check con-
ditions. The continuous wheat treatment showed a seed increase in the soil regardless of the herbi-
cide used. Under rotation conditions the changes were less drastic, but in general weed-seed popula-
tions increased under the nonchemical conditions and either maintained a relatively stable level or
decreased under the herbicide treatments. This provides an outstanding example of why a diversity
of herbicides is needed for any one particular crop. The use of herbicide rotations or alternative
herbicides can also contribute to a lessening of potential environmental contamination due to the
continual variation in chemical structures being used on a given site. Thus there is less chance of an
accumulation of a herbicide or of off-type organisms or wildlife becoming adapted to a specific struc-
ture.
The importance of weed control as a major element of integrated pest control in agricultural
crops has been frequently overlooked. Integrated control involves a program of pest control that
utilizes all the control means to the best possible degree. Unfortunately, many feel that these in-
volve only insect-control procedures. They should include cultural practices that minimize the
potential for the pest or enhance the ease of control—such as favoring natural predators, use of
favorite plant species as trap crops, and the elimination of weeds that act as breeding grounds where
insects or diseases increase and later invade the developing crop. Integrated pest controls should
therefore control all types of pests in the field, not just insects.
The use of herbicides for weed control, however, does not eliminate the need for sound cul-
tural practices, preventive methods of weed control, and good management. Most weeds in culti-
vated crops are still controlled by nonchemical methods, that is, mechanical, cultural, and biologi-
cal. Weed control with herbicides places a premium on the careful integration of weed-control
methods with all other cropping practices. The most dependable results in weed control are cur-
rently achieved by using as many of the various methods of weed control as feasible in any given
situation. Today's farmer does not have many alternatives that exclude herbicides in an integrated
weed program. He must produce as efficiently as possible or go out of business. The trend of in-
creasing farm size and decreasing labor supply has left the agricultural producer more and more
dependent on herbicides. The available alternatives, at least those that are currently feasible and
economical, are already being used to a great extent in integrated weed-control programs.
Major steps in the reduction of the total amount of herbicides used per given unit area are
becoming more and more possible through various types of research into factors influencing the
activity of herbicides. Changes in herbicide formulations, methods of applying the herbicide,
minimum effective dose studies, etc., tend to reduce to the-greatest extent possible the amount of
herbicide being applied to any given area.
Shifts. The use of herbicides or any intensive weed-control practice to control a specific group
of weed species has caused changes in species composition. The common herbicide 2,4-D reduces
annual broadleaf weeds, so that annual grasses tend to increase in population and density. The use
of trifluralin for many years to control annual grass weed species in southern broadleaf crops has
resulted in a definable increase in the population of resistant broadleaf weed species. Such weed-
population changes have occurred all over the country and are continuing. There is no reason to
expect this problem to decrease as long as a standard herbicide is widely used in a specific crop.
The most effective way of economically attacking such ecological shifts is through the use of alter-
native practices and alternative herbicides. However, herbicide rotation requires the availability of
several herbicides for a specific crop in a specific area of the country. The herbicides that can be
used in soybeans in the Corn Belt or Eastern United States are quite different from those that
would do an acceptable job of weed control in soybeans in the Mississippi Delta. Sorghum herbi-
cides available for the northern Great Plains cannot be used safely in sorghum grown in the southern
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Great Plains. Thus farmers need a greater arsenal of herbicides for use in cultivated crops, at a time
when the list of available herbicides is decreasing. To produce crops economically without undue
environmental contamination, the grower must have flexibility in chemical usage. New and safer
methods of testing and using herbicides will ensure hitting the target with a minimum effective dose
and the least likelihood of environmental contamination. It appears probable that with adequate
research additional herbicides will be discovered for specific uses that will prove safer to the
applicator, the consumer, and the environment than those now available.
References
Adkisson, P. L. (Chairman), 1970. Use of Agricultural Pesticides in Texas, A Report of the Gover-
nor's Science Advisory Panel on the Use of Agricultural Chemicals, Texas A&M University,
College Station. 65 pp.
Brickey, J., 1965. Spreckels Sugar Beet Bulletin, 29, 26.
Buchanan, G. A., and Burns, E. R., 1970. Weed ScL, 18, 149-154.
Burnside, O. C., and Coleville, W. L., 1964. Weed ScL, 12, 109.
Burnside, O. C., and Wicks, G. A., 1964. Weeds, 12, 307-310.
Burnside, O. C., Wicks, G. A., and Fenster, C. R., 1964. Weeds, 12, 211-215.
Burnside, O. C., Wicks, G. A., and Fenster, C. R., 1969. Agronomy Journal, 61, 297-299.
Cates, J. S., and Cox, H. R., 1912. Bureau Plant Ind., USDA Bull. 257.
Danielson, L. L., 1970. FAO International Conference on Weed Control, pp. 245-259.
Dawson, J. H., 1965. Weeds, 13, 245.
FAO International Conference on Weed Control, 1970. Technical Papers of the FAO International
Conference on Weed Control. 668 pp.
Garner, T. H., Bowen, H. D., and Luscomb, J. A., 1958. Cotton Gin and Oil Mill Press, 59, 30-32.
Gunther, F. A., 1970. Residue Reviews, vol. 33.
Hayes, W. J., Jr., 1964. Archives of Environmental Health, 9, 621-625.
Hayes, W. J., Jr., and Perkle, C. L, 1966. Archives of Environmental Health, 12, 43-55.
Hill, G. D., McGahen, J. W., Baker, H. M., Finerty, D. W., and Bingeman, C. W., 1955. Agronomy
Journal, 47, 93-104.
Holstun, J. G., Jr., Wooten, O. B., Jr., McWhorter, C. G., and Crowe, G. B., 1960. Weeds, 8, 232-243.
Holstun, J. G., Jr., 1963. Weeds, 11, 190-194.
Knake, E. L., and Slife, F. W., 1962. Weeds, 10, 26-29.
Knake, E. L., and Slife, F. W., 1965. Weeds, 13, 331-334.
Knake, E. L., and Slife, F. W., 1969. Weed ScL, 17, 281-283.
McWhorter, C. G., Wooten, O. B., and Crowe, G. B., 1956. Proc. Southern Weed Conf., 9, 19-31.
McWhorter, C. G. and Holstun, J. T., Jr., 1957. Proc. Southern Weed Conf., 10, 31-38.
National Academy of Sciences, 1968. Principles of Plant and Animal Pest Control, vol. 2, Weed
Control Publication 1597, National Academy of Sciences, Washington, D.C., 471 pp.
Shadbolt, C. A., and Holm, L. G., 1956. 4, 111-123.
Thompson, H. C., Wessels, P. H., and Mills, H. S., 1931. Cornell Univ. Station Bulletin 521.
U.S. Department of Agriculture, 1970. Agricultural Statistics, U.S. Government Printing Office,
Washington, D.C.
Weatherspoon, E. N., and Schweizer, E. E., 1969. Weed ScL, 17, 464-467.
Weed Science Society of America, 1974. Herbicide Handbook of the Weed Science Society of
America, 3rd ed., 430 pp.
Wilson, H. P., and Cole, R. H., 1966. Weeds, 14, 49-51.
Yarrick, B. E., 1946. California Citrog., 31, 318.
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Fruit and IMut Crops
General Principles and Practices.—Orchards produce fruits such as apples, pears, prunes, and
oranges, and nuts such as walnuts and almonds. Small fruits include fruits such as grapes, strawber-
ries, cranberries, and raspberries. The culture of these fruits is widely distributed throughout the
United States, with about 11 million tons of fruit, excluding citrus produced in 43 states each year
(Lange, 1970). Weed control in fruit and nut crops is a problem of considerable proportions.
Weeds in deciduous fruit trees in California alone are estimated to cost the growers approximately
$36 million per year, half of which is for weed-control programs and the other half is from losses
due to weeds (Lange, 1968). In California citrus crops, total costs of both control measures and
weed losses were estimated to be $23 million in 1964 (California, 1964). Weeds compete with trees
and vines for water, nutrients, and, in young plants, light. They facilitate attack from rodents,
insects, and pathogens. They interfere with management operations. They may reduce yield and
quality of the crop. In some cases they may conceal poisonous snakes, which quite obviously
interfere with harvest operations.
The establishment of orchards represents a major investment. The average time for orchards to
be commercially self-sustaining ranges from 4 to 5 years for peaches and plums to 9 to 10 years for
apples and walnuts (Lange, 1970). All the fruit and nut trees under discussion are perennial. Some
plantings are kept bare continuously; in others, areas between the tree rows are planted with peren-
nial sod or an annual cover crop. These plantings may help to prevent erosion and aid in water
penetration.
Methods of Control.—Common methods of weed control in the United States are tillage or
mowing, often in combination with herbicides. Flaming is sometimes used. Tillage is easy, equip-
ment is readily available, and timing is often flexible. Annuals are easily controlled, and perennials
can be controlled through carbohydrate starvation by repeated operations. However, repeated til-
lage operations can cause soil compaction and create plow soles or impervious layers beneath the
surface layer. Mowing is fast and cheap and helps to maintain vegetation for erosion control. It is
ineffective close to the trees, however, and on prostrate-type weeds. Vegetation that can compete
with the crop is still present. Flaming or burning is relatively cheap and easy, but repeated treat-
ments (up to 20) are needed to control perennial weeds. There is also a danger of injury to the
crop.
Grazing animals can be used among large trees, but they often injure small trees and shrubs. In
addition, they are difficult to manage, and unpalatable weeds may become predominant. Hand
labor offers one possibility of control adjacent to the base of the trees, but the cost of hand labor
has become almost prohibitive on a commercial scale.
The use of herbicides in orchards and on berry farms has increased dramatically. Herbicide use
on fruit and nut trees increased from an estimated 5000 acres in 1959 to 267,000 acres in 1962
(Shaw, 1964). It has been estimated that over 500,000 acres were treated in 1965 (USDA, 1968).
This increase in use has continued since.
Herbicides are usually applied in 4- to 6-foot strips along the tree rows, with mowing or tillage
used in the middle. This results in a 50-percent reduction in mowing or tillage operations in or-
chards because it eliminates the need for the mechanical operation to be carried out in two direc-
tions. Complete herbicide coverage is sometimes used, particularly if basin or furrow irrigation is
utilized.
Herbicide use, as indicated by its rapidly increasing popularity, offers some definite advan-
tages. Increased tree growth and increased yields have been demonstrated with chemical weed con-
trol as compared with clean cultivation or sod culture. These increases are especially dramatic
during the early stages of crop establishment and commercial production. In one experiment, for
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example, Leyden (1969) showed that yields of grapefruit in 1966 and 1967 were 95 and 107 kilo-
grams per tree for complete chemical control, 10 and 74 kilograms per tree for clean culture, and 4
and 13 kilograms for sod culture, respectively. The trees had been planted in 1960. Soil compaction
is reduced when mechanical cultivation is eliminated. Conversion from mechanical weed control
alone to a combination using herbicides reduces root and trunk damage from equipment, eliminates
weed competition, and generally results in a more healthy crop (Jordan and Day, 1970).
Air and soil temperatures seem to be higher in orchards under chemical weed control than
under clean cultivation or sod culture. Less freeze injury and more rapid recovery have been noted
in herbicide-treated orchards (Leyden, 1969).
A variety of herbicides are used in orchards and on small fruit. Repeated applications of weed
oil and, more recently, paraquat are used as quick-acting contact materials. These materials have no
soil activity. Their selectivity is based on avoiding contact with the foliage of the crop. Several
soil-active compounds have been introduced for fruit and nut trees, including diuron, simazine, tri-
fluralin, dichlobenil, and terbacil. Selectivity in these materials depends on the difference between
the crop and the weeds in depth, of rooting. These herbicides tend to remain in the upper layers of
the soil and eliminate shallow-rooting weeds but do not contact crop roots in sufficient concentra-
tions to cause damage. For this reason, complete ^dependence on soil-active herbicides can result in
an increase in deep-rooted perennial weeds like field bindweed, Canada thistle, and johnsongrass.
Furthermore, each herbicide is ineffective on certain annual weeds, so that repeated use of the same
herbicide can convert the crop area into a solid stand of the resistant weed. In addition, resistant
strains within a species may survive, resulting in a highly resistant population over a period of time
(Ryan, 1970). Therefore alternating among various herbicides is generally a recommended practice.
Some foliage-applied, translocated herbicides are also used, including 2,4-D and dalapon. The
compound 2,4-D is toxic to most fruit and nut trees if it contacts the foliage. Only nonvolatile
formulations must be used, and shields are often used to prevent spray drift onto the leaves.
Herbicides are nearly always applied by ground sprayers in fruit and nut orchards, so spray
drift is a minimal problem. Because the crop itself is sensitive to many of the chemicals used if con-
tact is made with roots and foliage, nonvolatile foliage herbicides or soil-active compounds that do
not move readily in the soil are used. Minor amounts of herbicides could possibly move out of
treated areas with irrigation water or through sheet erosion. As weed oils are known to evaporate,
large-scale usage could contribute to air pollution.
The efficacy of several herbicides used in perennial crops depends directly on their persist-
ence. Unlike the situation with many annual crops, where persistence beyond the growing season is
a disadvantage, extended soil life may be a distinct benefit in perennial crops, where rotation is not
a factor. Such compounds as diuron, simazine, and terbacil may last from 1 to 2 years in the soil.
However, because these herbicides are relatively immobile in the soil, adverse environmental effects
are not probable.
Use of Alternatives.—Nonchemical methods of weed control are still feasible in fruit and nut
orchards, but total dependence on these methods is not practical in many situations. The elimina-
tion of weeds from around the base of trees and vines is necessary, but it is very difficult by
mechanical means. Damage to trunks and roots, soil compaction, and reduced yields are common
results from mechanical weed control. Hand labor is becoming too expensive for economical pro-
duction. Biological control by grazing animals is a possibility, but it introduces a series of manage-
ment problems (predators, water supply, contamination of crop by manure, etc.) (Jordan and Day,
1970; Lange, 1970). A combination of chemical and nonchemical methods seems to offer the more
practical approach in most situations.
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Need for Herbicides.—Herbicides provide the most efficient and economical method of weed
control in many orchard and small fruit crops. Where chemicals have been used, orchards are warmer,
trees are more vigorous, and yields are higher (Jordan and Day, 1970). A choice of herbicides is
necessary because of the variety of crops, weed species, and cultural and environmental situations in
which crops are grown. Rotation of herbicides is desirable to prevent a buildup of strains or species
resistant to one herbicide. With an ever-increasing cost-price squeeze facing agricultural producers,
it is essential that such beneficial tools as herbicides continue to be available.
References
California State Chamber of Commerce, 1964. Report of Statewide Weed Control Committee, p.
39.
Jordan, L. S., and B. E. Day, 1970. FAO Intern. Conf. Weed Control, Davis, Calif., pp. 128-142.
Lange, A. H., 1968. Calif. Agric., 22, 8.
Lange, A. H., 1970. FAO Intern. Conf. Weed Control, Davis, Calif., pp. 143-162.
Leyden, R. F., 1969. Proc. 1st Intern. Citrus Symposium, 1, 473.
Ryan, G. F., 1970. Weed Sci., 18, 614.
Shaw, W. C., 1964. Weeds, 12, 153.
U.S. Department of Agriculture, 1968. Extent and Cost of Weed Control with Herbicides and an
Evaluation of Important Weeds, Agricultural Research Service Publication 34-102. pp. 43-46.
Solid-Seeded Annual Crops
General Principles and Practices.—Solid-seeded annual crops include small grains (rice, wheat,
barley, oats, and rye) and flax. In the future, this category may include many other crops (e.g.,
corn and beans) now grown in rows because of the need for cultivation and because of planting and
harvesting operations. In some areas, herbicidal weed control and the development of new har-
vesting equipment have made it possible to grow snap beans in solid stands.
In the United States rice is grown primarily in the South and in California. Most other small
grains are grown widely throughout the country. Upland cereals are drilled in 7- to 14-inch rows.
Most of the rice in this country is grown in diked paddies and flooded. It may be drilled, seeded
into the water from the air, or transplanted.
The number of weed species that commonly infest rice has been estimated to be at least 30
and, for other small grains, 35 (NAS, 1968, p. 254). Weeds appearing in rice may be aquatic as well
as terrestrial in nature. These weeds can be extremely competitive. In the Pacific Northwest, grass
weeds like annual ryegrass have reduced wheat yields from 75 bushels per acre in the best control
treatments down to 2 bushels per acre in the weedy plots (Aldridge, 1971).
Upland small grains include both fall- and spring-sown types. Weeds found in winter grains are
primarily winter annual weeds or weeds that germinate in early spring; those infesting spring grains
are largely early-maturing summer annuals and perennials.
Methods of Control.—In a solid-seeded annual crop the possibilities of nonchemical control are
limited. No successful biological agents have been introduced to date. However, various farming
techniques contribute to reduced weed populations and should be considered in management sys-
tems. Dry fallowing to control perennial weeds and the use of weed-free seed can help establish
clean crop stands. Shallow tillage after planting (blind tillage) can sometimes be used to control
weeds that germinate faster than the crop, but this technique is limited in value since most weeds
germinate over an extended period. Crop rotations can interrupt the life cycle of troublesome
weeds and reduce their population. An example is downy brome in wheat, which can be held to
manageable levels in the Great Plains by rotating infested fields to a spring-seeded row crop, such as
grain sorghum, for 1 to 2 years. Weeds may be encouraged to germinate, then be eliminated with
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shallow tillage prior to planting. This can be helpful, particularly if the major weed species tends to
germinate all at once.
In rice, water management is a critical factor influencing levels of weed infestation and deter-
mining the species present. Flooding to a depth of 4 to 8 inches helps control barnyardgrass seed-
lings, but may cause an increase in aquatic weeds. Timely drainage can reduce some weeds such as
algae (Smith and Shaw, 1966).
Herbicides are becoming more widely used in all small grains. In 1966, 80 percent of U.S. rice
acreage was treated with propanil and 50 percent was treated with phenoxy herbicides (Smith,
1967). The percentage of wheat and other small grains treated with herbicides is considerably less
than that of rice, with approximately 35 percent of wheat acreage treated (USDA, 1966). Until
recently, major herbicides used in small grains and flax were for broadleaf control. After the mid-
19408, 2,4-D and other phenoxy herbicides were widely used in the solid-seeded annual crops.
However, improvement in the control of broadleaves was accompanied by an increase in 2,4-D-
resistant broadleaves (e.g., wild buckwheat, blue mustard, and knotweed) and an increase in resist-
ant grass weeds. Wild oats, annual bromes, annual ryegrass, green foxtail, and other grasses became
more severe in upland grains, while such grasses as barnyardgrass and sprangletop increased in rice.
New, short-strawed varieties of grains have been introduced. These high-yielding grains can profit
from increased fertility levels without lodging, but their shorter stature causes them to be less com-
petitive to weeds. Also, the increased levels of nitrogen and phosphorus required for optimum crop
production may also stimulate the growth of grass weeds (Appleby, 1971; Smith, 1967). All of
these changes have increased the need for new herbicides.
Several new herbicides have been introduced that are effective against weeds not controlled by
2,4-D and other phenoxys. Barban, diallate, and triallate are used for wild oat control in grains and
flax. Diuron is used in the Pacific Northwest for the control of annual ryegrass in winter wheat and
barley. Propanil and molinate are grass killers for rice. Bromoxynil, linuron, terbutryn, and
dicamba have been registered for use in wheatfields primarily against 2,4-D-resistant broadleaf
weeds.
Somewhat less than complete weed control is required in most grains. A few weeds can gener-
ally be tolerated without severe reduction in yields. However, some weeds (e.g., annual ryegrass and
wild oats) become quite competitive, and even sparse stands can reduce yields. Other weeds, such
as sunflower, may interfere with harvest operations. Also, incomplete control may contribute to
increased weed-seed populations in the soil.
As with most herbicide treatments, the degree of success of herbicide applications in grains is
varied. In general, 2,4-D has been fairly consistent for adequate control of susceptible weeds. The
performance of newer herbicides, particularly that of soil-applied ones, has been less consistent.
Nearly all herbicides used in solid-seeded annual crops are reasonably short-lived in the envi-
ronment, most of them having a soil life during the growing season of 8 weeks or less (WSSA,
1970). A few herbicides for grain crops are included in chemical families generally considered to
have significant persistence; examples are diuron (phenylurea) and terbutryn (triazine). However,
recommended rates are low because the selectivity of grains to these compounds is limited, and, at
low rates, such materials have not caused injury to subsequent crops. In one study, runoff water
from fields in the Willamette Valley of Oregon was analyzed for the presence of herbicides. Although
large amounts of herbicides are used in the Willamette Valley in small grains, orchards, grass-seed
crops, and others, no residues were found (Brannock, 1967), indicating that movement of phenyl-
ureas and triazines in the water is not a significant factor when used at low rates in cropland.
Probably the major undesirable effect from herbicides for grain crops has been spray drift onto
nontarget areas. Drift injury from 2,4-D, mostly from aerial applications, is common throughout
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the United States. Propanil applications to rice in California have resulted in considerable injury to
prune trees. The use of alternative herbicides has reduced drift injury significantly; an example is
the use of bromoxynil, terbutryn, and linuron in the Pacific Northwest in areas surrounding vege-
table and fruit crops. Continued development of new application methods, such as foam, spray
thickeners, and improved design and placement of nozzles, will also reduce the spray-drift problem.
Use of Alternatives.—The use of herbicides in cropland should never replace good farming prac-
tices. As already mentioned, several nonchemical practices can help reduce weed populations. Such
alternative practices should always be seriously considered and used when practical. Many situations,
however, make the use of some techniques inappropriate. Most noxious weeds germinate after the
crop has been planted and is emerging. This eliminates delayed tillage and blind tillage as feasible
practices. Cultivation in solid-seeded crops is of questionable use, particularly in areas where fall-
planted fields are wet or frozen in the winter. Hand removal of weeds is economically impractical in
the extensive plantings of low-value crops. Crop rotations may be helpful at times, but in some areas
rolling hills and low rainfall prevent the production of alternative crops.
Need for Herbicides.—If herbicides become unavailable for use in solid-seeded annual crops,
the impact could be serious, especially in rice and in small grains in certain areas. The severe compe-
tition from weeds coupled with the lack of feasible alternatives in many cases would eliminate pro-
duction of small grains from much of the Pacific Northwest and parts of the Northern and North-
eastern States. Herbicides are used less extensively in small grains in the Great Plains. The need for
several different herbicides has become more apparent as species and strains resistant to specific
herbicides have increased. The wide diversity of environmental conditions, cultural practices, and
weed species has already been pointed out, emphasizing the need for flexibility and diversity of
tools available.
References
Aldridge, J. C., Olson, P. D., and Appleby, A. P., 1971. West. Soc. Weed Sci. Res. Prog. Rpt, pp.
96-98.
Appleby, A. P., 1971. Weed Control Research Report—Small Grains, 1971, Oregon State University
(mimeographed).
Brannock, D., 1967. Unpublished data, Department of Agricultural Chemistry, Oregon State Uni-
versity.
Nalewaja, J. D., and Arnold, W. E., 1970. FAO Intern. Conf. Weed Control, Davis, Calif., pp. 48-64.
National Academy of Sciences, 1968. Weed Control, Publication No. 1597.
Smith, R. J., Jr., 1967. Asian-Pacific Weed Control Interchange Proc., 1, 67.
Smith, R. J., Jr., and Shaw, W. C., 1966. Weeds and Their Control in Rice Production, U.S. Depart-
ment of Agriculture Handbook 292.
U.S. Department of Agriculture, 1966. Quantities of Pesticide Used by Farmers in 1966, Economic
Research Service Report No. 179.
Weed Science Society of America, 1970. Herbicide Handbook, W. F. Humphrey Press, Geneva,
N.Y.
Solid-Seeded Perennial Crops
The solid-seeded perennial crops of the United States are primarily improved hay and pasture
species. Such croplands generally receive more management than native pastures and ranges and are
periodically reseeded due to disappearance of the desired high-yielding and high-quality introduced
species. As time passes after the introduction of the desired species, there is frequently a slow re-
duction in the population of the desired species and an increase in the population of the better
adapted weed species. Most of the weed species are either nonutilizable as forage or have much
lower protein or other quality factors. Trends toward dominance by weeds can be slowed or
changed by judicious use of mechanical and chemical weed-control methods as well as by manage-
ment procedures. Due to the wide variation in species used across the country and to climatic and
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soil variations, no one chemical or management practice is uniformly used. Nevertheless, many of
these perennial crops can be maintained at a high productive level by present management tech-
niques, which usually include some form of chemical weed control.
A major problem in such perennial crops is that perennial weeds are often favored by the same
management practices that favor the crops.
Careful consideration must be given to selecting the control methods that are most effective
for a particular pasture or hay crop and its specific environmental conditions. A management
approach satisfactory in one situation may not work well in another. One management practice
that must always be considered is the time or frequency of harvesting, whether by mechanical
means or by livestock. Incorrect harvesting intervals can rapidly lead to the depletion of the carbo-
hydrate reserves in the forage plants, with a consequent rapid deterioration in the quality of the
perennial crop. Few mechanical control procedures are available for use in these solid-seeded peren-
nial forage crops. Any procedure that would stir the soil would dislodge the desired crop as well as
any weeds. Judicious cutting of weed seed heads can prevent some seed production, but it may also
inhibit the development of the crop species. Such methods also have little effect on the control of
perennial weeds. Liming and fertilization are often effective in encouraging the crop plant in the
competitive struggle with invading weed species. However, some weed species are also favored by
fertilization and thus become greater problems on the more fertile soil.
Solid-seeded perennial crops, such as alfalfa or legume grass mixtures, are particularly vulner-
able to weed competition during their seedling stages. Almost invariably the crop germinates and
grows slowly, thus providing the opportunity for rapidly developing weeds to overtop and severely
shade them. In one study in Indiana, broadleaf weed seedlings were found to grow five times more
rapidly than the legume seedlings (Klingman, 1970). In the past, growers have frequently planted a
companion crop of cereal grains or other crops in an effort to reduce weeds in spring-seeded forage
crops. However, research in many northern and northeastern states has shown that companion crops
(e.g., barley and oats) may injure slow-growing forage species as much as do weeds (Klingman, 1970).
Some planting or other management practices have been developed that favor rapid germination and
growth of legumes to assist them in competing with weeds. Band seeding, crop rotations that reduce
the prevalence of weed seeds in the soil, thorough seedbed preparation, mowing, and the use of herbi-
cides are all practices that have been developed to help forage seedlings in becoming established.
Each method involves the integration and use of certain weed-control principles and practices.
The time of planting of the forage crop has a major influence on the weed species to be found
in it. Spring-planted crops frequently have problems with summer annual weeds like pigweed,
smartweed, mustard, and foxtail. Late-spring plantings have a different set of weed problems.
Late-summer or fall seeding probably causes the presence of winter annuals and biennial weeds,
which characteristically start their growth at the onset of cool temperatures. Some of these are
chickweed, henbit, wild mustard, pepperweed, and yellow rocket and cheat.
Herbicides are a major management tool in the establishment and culture of solid-seeded
perennial crop species. Here again, a variety of herbicides are needed or used to fit a variety of envi-
ronmental conditions and prevalent weed species. The development of herbicides that selectively
kill weeds with minimal injury to forage legumes has caused some shift from seeding with a com-
panion crop to seeding the desired species alone. In recent years the development of preplant herbi-
cides to be applied before the planting of a forage crop has led to a major change in seeding proce-
dures in some areas. Application of EPTC or Benefin and their immediate incorporation into the
soil before planting controls many annual grasses (Muzik, 1970). However, both of these com-
pounds are relatively expensive in relation to the value of the crop being produced.
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More frequently, chemical weed control in solid-seeded perennial crops involves the use of
postemergence treatments. This is particularly true when the forage crops can be seeded in the fall
rather than in the spring. Most forage legumes (including alfalfa) can tolerate 2,4-DB, CIPC,
dinoseb, dalapon, or other herbicides that can control winter annual weed species. The use of herbi-
cides in "stale seedbeds" is another means of controlling weeds in new seedings. This involves pre-
paring the seedbed several months before planting the desired crop. Some time before seeding, the
weeds that germinate are killed with herbicides that do not persist long enough in the soil to inter-
fere with the development of the young forage-crop seedlings. Since the soil is not disturbed by
tillage, new weed seeds are not brought to the surface, and a lengthy relatively weed-free period
may be available for establishment of the forage seedlings.
Legumes grown for hay compete with most weeds as long as the stands remain dense and the
plants are vigorous. However, when the forage crop is dormant, it is less able to compete with
winter annual weeds. Selective control of annual grasses and perennial weeds cannot be successfully
accomplished at present. Preventive measures and mowing control broadleaf weeds but often in-
crease the problem of weed grasses. Thus alternative procedures for weed control that might be
developed will frequently result in a lessening of the crop stand, which results in increased competi-
tion from weeds. Once stands begin to weaken, a rapid invasion of weed species occurs.
Seed production in crops like alfalfa requires lower plant populations than are needed for hay
production. Consequently, seed crops often provide less competition to weeds than the same
species grown for hay. Furthermore, seed production schedules do not include frequent mowings,
which might control some of the weeds. Practices favoring the competitive ability of the legume
plant often cannot be utilized for controlling weeds in seed crops. Heavy vegetation growth may
drastically reduce seed yield. Some tillage operations are occasionally used for weed control under
such situations. Flaming of legume stubble in the early spring between hay cutting and seed crops
may be utilized to destroy seedlings and attack dodder and other annual weeds. However, cultural
practices alone seldom result in complete weed control in legume fields. Herbicidal control
methods have been developed for these situations. Substituted urea (e.g., diuron) or triazine (e.g.,
simazine) herbicides have been developed for some of these situations. They are particularly effec-
tive for controlling the winter annual weeds that occur in the crops.
Many of the same principles of weed control used to establish legumes also apply to the estab-
lishment of grasses, although the herbicides utilized may be different. Annual broadleaf weeds offer
severe competition to grasses. However, after the seeded grasses reach the two- to four-leaf stage of
growth, they may be able to tolerate low rates of such herbicides as 2,4-D and dicamba. Weed
grasses are quite difficult to control. In Oregon herbicides have been used effectively before and
after grass planting. The seedbed is prepared in the fall, and the soil is treated with IPC and 2,4-D in
January to control weeds and volunteer crop plants. Paraquat may be applied to later germinating
weeds in March just before seeding the perennial grasses. By fall the perennial grasses may be so
well established that the soil can be treated with diuron to control winter annual weeds.
An outstanding example of the importance of weed control and grass establishment was dem-
onstrated in the southern United States. Coastal Bermuda grass planted in May was sprayed immedi-
ately afterward with simazine. Weeds were eliminated, and the grass yields amounted to 3.7 tons
per acre of dry matter, as compared with 1.9 tons per acre of Bermuda grass and 1.6 tons per acre
of weeds from an untreated plot. The treated area yielded 9.5 tons per acre the following year, but
the untreated plot yielded only 6 tons per acre of Bermuda grass. The weed-control practice that
was employed made possible better utilization of fertilizer by the forage grass, earlier grazing, and
higher quality forage (Monson et. al., 1971).
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References
Klingman, D. L., 1970. FAO International Conf. on Weed Control, pp. 401-424.
Monson, W. G., Burton, G. W., Wilkinson, W. S., and Dumford, S. W., 1971. Agronomy Journal,
63, 928.
Muzik, T. J., 1970. Weed Biology and Control, McGraw Hill, pp. 238-252.
INDUSTRIAL AND URBAN SITES
Utility Rights-of-Way
Electric Transmission Lines.—All woody vegetation that could ultimately reach the electric
conductors on transmission lines must be controlled to prevent shorting of circuits and subsequent
damage to equipment and loss of service. Many utilities have sought to eliminate all woody vegeta-
tion from transmission rights-of-way., but the current trend is to control only tall-growing trees and
shrubs, allowing low-growing woody vegetation to remain. Transmission line rights-of-way are usu-
ally 100 to 500 feet wide.
An access road is also required for the maintenance and repair of the transmission structures
and lines. Some of these roads are improved, but most have a cover of herbaceous vegetation.
Grass is the preferred cover in most areas. No woody vegetation should be present on the access
road.
Most utilities also remove any "danger timber" on, or adjacent to, the right-of-way that could
reach and damage the transmission towers, poles, or conductors if it fell or was knocked down. In
areas subject to fire, all vegetation is removed around wood poles and towers.
Electric Distribution Lines.—All woody vegetation must be controlled before it reaches the
electrical conductors. Access roads are not usually maintained on the right-of-way, but it should be
accessible by foot or vehicle. Brambles, briars, and poison ivy restrict access and should be re-
moved. Distribution rights-of-way are usually 30 to 50 feet wide. In areas subject to fire, all vegeta-
tion is controlled around wooden poles.
Communication Lines.—Requirements for vegetation control are similar to those for electrical
distribution lines. Communication cables are often carried on the same poles as electric con-
ductors. Contact of the cables with vegetation is less critical, but cable wear due to friction with
woody vegetation must be eliminated.
Gas and Fluid Transmission Lines.—Woody vegetation that would limit access must be con-
trolled, but it is desirable to maintain a herbaceous or shrub cover to aid in detecting leaks in buried
pipelines. Surface pipelines require total vegetation control for access, inspection, maintenance, and
air circulation.
Mechanical Control
Hand Cutting.—Vegetation on most utility rights-of-way can be maintained by hand cutting. It
can be cut totally or selectively, although labor costs are higher for selective cutting. Annual
cutting is usually required. Disposal of the cut material by chipping is usually necessary, since burn-
ing is prohibited in many areas. Initial clearance of rights-of-way is by cutting and burning or
chipping. Marketable wood products may be sold. The main limitation to hand cutting is its cost.
The work is also difficult and hazardous.
Seeding or Planting.—Many rights-of-way can be seeded or planted with grass, hay, Christmas
trees, or crops. In metropolitan areas it is often possible to maintain rights-of-way by regular
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mowing once grass is established. Maintenance costs are high, but good public relations are fos-
tered. Where the soil and location are suitable for crops, they may be grown by a permit or
easement system.
Bulldozing, Disking, or Chopping.— Brush control by bulldozing or disking is positive and non-
selective. The right-of-way is usually converted to annual broadleaf vegetation such as ragweed,
fireweed, and kochia. On hilly terrain erosion is a problem after bulldozing or disking, and the
establishment of vegetative cover is difficult. Rugged terrain restricts or prohibits the use of a bull-
dozer. "Bush-hogging" with a heavy-duty mower can be used, but regular mowing is required and
thorny vines often take over the site.
Burning.—Burning usually cannot be used on rights-of-way because of heat damage to towers,
poles, and cables; the resulting smoke and air pollution; and potential damage to adjacent areas.
Chemical Control
Chemical vegetation control can be applied to utility rights-of-way using broadcast or selective
techniques (see Table 1).
Broadcast Applications.—The stem-foliage spray is the "standard" method of controlling brush
on utility rights-of-way. A mixture of herbicide concentrate and water is applied to all the leaves
and stems of the brush to be controlled. As the spray season progresses and brush becomes harder
to kill because of reduced herbicide absorption due to plant maturity, 10 to 15 percent fuel oil may
be added to the mixture. The spray is usually applied by hand-held brush guns at a volume of 150
to 500 (average 300) gallons of spray solution per acre, depending on brush density. The spray
applicator may walk and spray each clump of brush, or he may ride the spray vehicle and direct the
spray at the brush stems and foliage. Stem-foliage sprays give best results when applied during
periods of active brush growth—usually mid-May to mid-August in the United States. Most stem-
foliage sprays are applied by truck-mounted sprayers with positive-displacement pumps at pressures
of 200 to 400 psi. The average cost of chemicals for a stem-foliage spray is $30 plus $50 for labor,
for a total cost of $80 per acre.
The most commonly used herbicides are the following:
1. 2,4-D and 2,4,5-T mixtures, ester or amines (4 lb/100 gal)
2. 2,4,5-T, ester or amines (4 lb/100 gal)
3. 2,4-D and dichlorprop mixtures, ester or amines (4 lb/100 gal)
4. 2,4-D, ester or amines (4 lb/100 gal)
5. 2,4-D and picloram mixtures, amines (2.5 lb/100 gal)
6. AMS (50 lb/100 gal)
A variation of the ground stem-foliage method is the use of a fixed broadcast nozzle mounted
on a vehicle to apply a continuous herbicide spray pattern to the right-of-way. The average applica-
tion rate is 3 gallons of herbicide concentrate (12 pounds of phenoxy acid) in 50 to 100 gallons of
water. The amounts of herbicide per sprayed acre are similar for high-volume and fixed-nozzle
spraying. Application costs are lower for the fixed nozzle, but this method is effective only on level
terrain and brush of uniform height.
Dormant-cane broadcast sprays are used to control brush in areas where the risk of spray drift
to herbicide-sensitive crops makes it hazardous to spray during the growing season. Since dormant-
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cane sprays are applied when most woody plants have no leaves, fuel oil is used as a spray diluent
for bark penetration. The oil-herbicide mixture is sprayed on the stems and bases of the woody
plants, usually by crewmen riding on a vehicle and holding a brush gun. Fixed nozzles are some-
times used. The standard herbicide mixture is 6 pounds of phenoxy herbicide in 98.5 gallons of
fuel oil. Oil-soluble phenoxy-picloram combinations are sometimes used.
Dormant-cane broadcast sprays are very effective on such species as oak, ash, maple, and pine,
which are resistant to foliage sprays. Dormant-cane sprays of phenoxy herbicides are not effective
on root-suckering species, such as black locust, sassafras, sumac, and persimmon.
The average cost for dormant-cane treatments is $55 per acre for chemicals and $60 per acre
for labor, for a total cost of $115 per acre.
Aerial broadcast spraying is usually done in the growing season when vegetation is in full leaf.
It is most economical on rough, steep terrain or in swampy or inaccessible areas. Helicopters with
conventional spray nozzles may be used. Since prevention of spray drift to adjacent areas is usually
necessary, however, one of these industry-developed drift-control systems is generally used:
1. Bifluid invert system
2. Invert Spra-Disk System
3. R-511 + Norbak System
4. Microfoil boom
The volume of carrier used for aerial sprays varies from 5 to 30 gal/acre. Larger volumes are re-
quired for coverage as droplet size increases.
The average rate per acre is 3 gallons (12 pounds) for phenoxy herbicides and 2 to 4 gallons (5
to 10 pounds) of phenoxy-picloram mixtures. The average cost per acre is from $40 to $60. The
advantages of broadcast spraying are as follows:
1. Useful for heavy mixed brush
2. Quick topkill of rapidly growing brush
3. Elimination of easy-to-kill species
4. Most efficient method for initial control of right-of-way brush
The disadvantages of broadcast spraying are as follows:
1. "Brownout" of brush foliage
2. Elimination of many desirable low-growing plants that provide game food and cover and
soil protection
3. Drift potential of high-pressure or broadcast sprays
4. Heavy exposure of crews to herbicide sprays
5. Application of herbicide to nontarget areas
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Table 1. HERBICIDES FOR INDUSTRIAL WEED AND BRUSH CONTROL
Chemical
Primary use
Primary mode
of action
Rate
(Ib/acre)
Advantages
Disadvantages
Amitroleand Grass control; perennial
amitrole-T weed control; general
weed control; knock-
down of vegetation in
combination with other
herbicides
AMS Brush control near sensi-
tive crops and on
watersheds
Atrazine Residual weed control
Foliage systemic 2-10
Foliage contact; 50-200
root absorption
Root absorption
Bromacil Perennial grass control; Root absorption
residual weed control;
brush control
Bromoxynil Broadleaf weed control Foliage contact
where phenoxy mate-
rials are hazardous or
prohibited
Cacodylic acid Knockdown of vegetation Foliage contact
CBM
(chlorate-
borate
mixtures)
Dalapon
Dicamba
2,4-D
Dichlorprop
Dinoseb
Diuron
Knockdown of vegetation; Foliage contact
johnsongrass control
Postemergence grass con-
trol ; controls Johnson-
grass and Bermuda
grass
Broadleaf weed control;
brush control; usually
used with phenoxies
Foliage systemic
Broadleaf weed control; Foliage systemic
brush control; used with
other phenoxies
Brush control with other
phenoxies
Knockdown, oil fortifier Foliage contact
Residual weed control Root absorption
DSMA-MSMA Grass knockdown; Johnson- Foliage contact
grass control used with
phenoxies for brush
control
2-40
2-20
0.5-2
3-10
50-800
540
Foliage systemic; 0.25-10
root absorption
0.5-12
Foliage systemic 2-8
1-12
2-40
2-8
Broad spectrum, both
grass and broadleaf
weeds; no soil residue
Drift does not harm
sensitive crops
Seasonal weed control
Controls johnsongrass
No drift hazard; for
broadleaf control
Rapid disappearance
from soil
Easy to spread as
granules
Controls most grasses
Kills several resistant
brush species and
broadleaf perennials;
selective on grass
Low cost; broad spec-
trum; short soil
residue; selective on
grass
Kills oaks as well as
2,4,5-T; selective on
grass
Broad spectrum
Long lasting; little injury
to woody plants
Low cost; kills annual
grasses; repeat sprays
kill rhizome Johnson-
grass
Slow acting drift may
cause chlorosis in
susceptible plants
Corrosive; high rates
required; skin irri-
tation on pro-
longed contact
Poor on southern
grasses; annual
grasses reinvade
soon
Leaches readily; in-
jurious to desira-
ble woody plants
Ineffective on grasses
Caution needed in
application
High rates required
Retreatment usually
required
Drift injury to sensi-
tive crops
Drift injury to sensi-
tive crops
Drift injury to sensi-
tive crops
Stains; toxic; no
residual control
Poor on organic soils
Caution required in
application; needs
high temperature
for best results
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Table 1. HERBICIDES FOR INDUSTRIAL WEED AND BRUSH CONTROL-Continued
Chemical
Fenac
Primary use
Residual broadleaf weed
control; annual grass
control
Primary mode
of action
Root absorption
Rate
(Ib/acre)
3-18
Advantages
Kills many perennial
broadleaf weeds and
annual grasses; kills re-
sistant annuals; water
soluble liquid
Disadvantages
Slow acting; no
perennial grass
control
Herbicidal oils Knockdown of vegetation Foliage contact
10-100 gal Fast acting
Hexachloro-
acetone
Karbutilate
Linuron
Monuron
Paraquat
Picloram
Pentachloro-
phenol
Prometone
Silvex
Simazine
Sodium
arsenite
2,4,5-T
Oil fortifier for control of
railroad weeds and john-
songrass
Residual weed control;
brush control
Short-term residual control
alone or in mixtures
Residual weed control
Knockdown of grass and
broadleaf weeds
Brush control; broadleaf
annual and perennial
weed control; used
with phenoxies
Knockdown of vegetation;
oil fortifier
Knockdown and residua!
control of annual and
perennial broadleaf and
grass weeds
Brush control; broadleaf
perennial control
Residual weed control
Knockdown; residual
weed control
Brush control
Foliage contact
Root absorption
Root absorption
Root absorption
1-3 gal
2-20
1-4
2-40
Foliage contact 0.25-1
Foliage systemic; 0.25-8
root absorption
Foliage contact 10-20
Foliage systemic; 10-60
root absorption
Foliage systemic 1-8
Root absorption 2-40
Foliage contact; 4-8
root absorption
Foliage systemic 1-8
No residual action;
no perennial weed
control
Use as spot treatment;
basal spray for john-
songrass; short soil
persistence
Controls many perennials
and herbaceous brush
species
Short-term soil residual;
area may be reseeded
or planted in 3-4
months
Broad spectrum; controls
many perennials
Broad spectrum; no soil
activity
Broad spectrum; grass
very tolerant
Short persistence in soil
Controls southern grasses
at high rates; broad
spectrum; fast knock-
down
Kills oaks, persimmon,
and other brush
Little hazard to woody
plants; leaches little
Broad spectrum
Broad spectrum; versatile
and selective on grass
No dandelion control;
destroys ground
cover as brush-
killer
Many resistant
species
Leaches readily; in-
jures desirable
woody plants; no
plantain control;
poor on organic
soils
Hazardous to apply
Runoff injury; root
uptake injury by
desirable plants;
ash and alder
resistant
Toxic; causes skin,
eye, and respira-
tory irritation;
breaks down rubber
Adequate rainfall re-
quired to kill
perennials
Not effective on all
species; slow acting;
more persistent in
soil than other
phenoxies
No control of south-
ern grasses
Toxic to domestic ani-
mals and wildlife;
arsenic buildup; ille-
gal in many areas
Drift injury to sensi-
tive plants
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Table 1. HERBICIDES FOR INDUSTRIAL WEED AND BRUSH CONTROL-Continued
Chemical
Primary use
Primary mode
of action
Rate
(Ib/acre)
Advantages
Disadvantages
TBA
TCA
Perennial broadleaf con-
trol; brush control
Perennial grass control
Root absorption
Foliage contact;
root absorption
4-20 Effective on bindweed,
knapweed, and other
deep-rooted peren-
nials; controls conifers
50-200 Short soil persistence
High rates, requires
narrow spectrum
Corrosive; irritating
to apply
Selective Applications.—Basal sprays are used to selectively control individual stems or clumps
of brush. A herbicide-oil mixture is directed at a low pressure to the lower 12 to 18 inches of the
brush stem in a sufficient quantity to puddle around the base or root collar. The standard basal
spray concentration is 12 to 16 pounds of 2,4,5-T or a 2,4-D plus 2,4,5-T mixture per 100 gallons
of fuel oil or kerosene. A mixture of picloram and 2,4,5-T or 2,4-D and dichlorprop is also used.
The volume of spray per acre varies with the brush density but averages 100 to 150 gal/acre. Basal
sprays are used not as initial applications to dense brush but as "cleanup" sprays to remove resistant
species when easy-to-kill brush has been controlled. They can be applied at any season of the year,
whenever the brush is not wet. Hand or power equipment may be used.
A recent variation of the basal spray is the use of the backpack mistblower to apply a more
concentrated herbicide-oil mixture to brush. A mixture of 10 to 14 gallons of phenoxy herbicide
concentrate per 100 gallons fuel oil or kerosene (equal to active ingredient by weight of 40 to 56
lb/100 gal) is used. Although the spray solution is more concentrated, herbicide rates per acre are
about the same as in the case of conventional basal sprays since the volume per acre is from 25 to
40 gallons. A conventional basal spray application costs approximately $34 for chemicals and $45
for labor, for a total of $79 per acre. Mistblower basals cost $23 for chemicals and $35 for labor,
for a total cost of $58 per acre.
Stump sprays are used for initial right-of-way clearance or to control brush sprouting after
cutting. Oil-herbicide mixtures used for basal spraying are also used for stump spraying. The spray
solution is applied to the stump and exposed roots. Truck-mounted power sprayers, backpack
pump sprayers, or portable mistblowers are used to apply stump sprays. Average stump-spray costs
are $23 for chemicals and $25 for labor, for a total cost of $48 per acre.
The advantages of basal and stump spraying are as follows:
1. Selectivity: only tall-growing woody plants need to be sprayed
2. Can be applied at any season
3. Minimum disturbance to ground-cover vegetation
4. Little or no "brownout"
5. Good control of "resistant" brush species
6. Little or no injury to off-right-of-way vegetation
7. Economical on scattered brush
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8. Simple equipment can be used
9. Minimum environmental impact
The disadvantages of basal and stump spraying are as follows:
1. Poor control of root-suckering brush species
2. Too expensive on dense brush
3. Possible to miss some stems
4. Good supervision and instruction of spray crews needed
Soil/root treatments are usually applied as pellets or granules. Herbicides that are relatively per-
sistent in the soil and are active on woody plants are used for soil applications. Treatments may be
applied to individual brush clumps on a grid pattern (i.e., every 3 feet) or broadcast. Individual
clump or grid treatments are usually applied by hand; broadcast applications are made by hand
spreaders, truck- or trailer-mounted power spreaders, or helicopter-mounted spreaders. The herbi-
cides commonly used for brush control are picloram, karbutilon, fenuron, TCA-monuron, and
bromacil. The advantages of soil/root applications are as follows:
1. Can be applied selectively
2. Little or no equipment required
3. No drift problem
The disadvantages of soil/root applications are as follows:
1. High cost
2. Often injurious to ground-cover plants, which opens soil to erosion
3. Runoff injury adjacent to right-of-way
4. Easy to overdose
5. Soil persistence
6. Soil differences can affect results
7. Higher rates of herbicide required
Railroads
Yards and Switches.—It is necessary to maintain nearly 100 percent vegetation control for the
safety of men working on foot in the area, for proper functioning of switches, for visibility, and for
drainage. Vegetation control is difficult because the area is often high in carbon content from coal
residue; grain spillage causes heavy sprouting of crop and weed seeds; and the area between adjacent
tracks is subject to heavy leaching due to concentrated runoff from standing freight cars. The aver-
age annual vegetation-control costs are $50 to $150 per acre.
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Ballast.—Total vegetation control is necessary in the ballast area to maintain drainage to keep
the ballast free from fouling by soil or vegetation residue and to keep the ties dry to extend tie
life. Ballast is usually coarse crushed rock. Annual weeds are not common, but perennial weeds
often encroach from the berm area. The average annual vegetation-control costs are $10 to $30 per
acre.
Shoulders and Berms.—The shoulder and berm area is immediately adjacent to the ballast. It is
necessary to control large annuals, creeping perennials, and vines. Low-growing annuals can remain
if they will not creep into the ballast area. Woody shrubs, perennials, and vines often grow in this
area and extend into the ballast. The control of annuals has intensified the perennial and woody
plant problem in this area. The average annual vegetation-control costs are $20 to $40 per acre.
Ditches and Adjacent Rights-of Way.—Railroad rights-of-way usually have drainage ditches in
the track area. Herbaceous vegetation is desirable, but woody plants and vines must be controlled
to maintain drainage and to prevent encroachment of vines into the berm and ballast area. States
with strong weed-control laws often require the railroads to control noxious weeds in the right-of-
way area even though they are not detrimental to the operation of the railroad (e.g., Canada thistle,
knapweed, bindweed, and johnsongrass). The annual vegetation-control costs are $5 to $30 per
acre.
Bridges and Structures.—Total vegetation control is required in the area adjacent to bridges and
other structures, primarily for fire control. No vegetation residue is tolerated in this area. Most
railroad structures are partially or totally constructed of wood. The average annual vegetation-
control costs are $50 to $150 per acre.
Communication Lines.—Communication lines on wooden poles are often maintained on one
edge of the railroad right-of-way. Lines are usually 10 to 15 feet above the ground. Brush must be
controlled under these lines. Many railroads in arid areas control all vegetation under communica-
tion lines for fire control. Some require weed control only around the poles, but others need control
all along the line since communication cables are damaged by heat. The average annual vegetation-
control costs are $5 to $30 per acre.
Mechanical Control.—Vegetation in yards and switches can be controlled by hand cutting, but
no acceptable equipment is available for mowing. Freightears stand on the track much of the time,
and engines and cars move about at all times. Hand grubbing and trimming around switches is pos-
sible, but would need to be done weekly in many areas. Wet vegetation is unsafe even if trimmed
short in the walkways between tracks.
Ballast is periodically cleaned by machine. Vegetation in this area can be controlled by more
frequent lifting and cleaning.
Vegetation on shoulders and berms can be mowed on a regular basis. Equipment exists for this
use, and some railroads use it now. Vine control is difficult.
Mechanical weed control around bridges and structures is impractical since it would need to be
done on such a regular basis. Vegetation residue would have to be removed.
On the balance of the right-of-way and under communication lines vegetation can be hand cut
or mowed. The only limitations are cost and safety. Hand cutting brush is dangerous work, and
poisonous snakes are problems in certain areas.
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Chemical Control.*—Herbaceous weeds can be controlled by contact, translocated, or residual
herbicides, but railroads commonly use a mixture of all three. The herbicide mixture and rate are
determined by the weeds present, their location, and the degree of control needed. Where total
control is needed, high rates of residual herbicides are used. For ballast and berm areas, contact or
systemic herbicides combined with a low rate of residual material are commonly used. Granules are
often used in yards, switches, and around bridges and structures, but high-volume sprays applied by
spray train or highway-rail vehicles are used for ballast, shoulder, and berm weed control. A partial
list of herbicides and rates used by railroads for herbaceous weed control is given in Table 1.
Chemical control of woody plants on railroad rights-of-way is primarily accomplished by high-
volume (200 to 500 gal/acre) stem-foliage applications of phenoxy herbicides by spray trains
mounted on the track. Application by highway-rail trucks is used on a small fraction of the acreage
but is increasing. In areas adjacent to susceptible crops like cotton or tobacco, dormant-cane broad-
cast sprays or nonphenoxy, nonpicloram herbicides are used. The use of basal, cut-stump, and
granular applications is negligible on railroad rights-of-way and is confined to inaccessible or heavily
populated areas.
High-volume sprays are particularly suited for railroad application because of the ease with
which tank cars of water or oil can be carried through the center of the area to be sprayed.
The control of herbaceous and woody vines, such as trumpetcreeper (Campsis radicans),
peppervine species, redvine species, and various brambles (Rubus spp.), is more important for rail-
roads than for other industrial consumers because these vines will grow over the ballast and track
area, fouling the ballast, shortening tie life, and causing loss of traction.
Other Methods of Control.—Crops or hay can be grown on portions of some railroad rights-of-
way, but the grazing of meat or dairy animals is not practical.
Industrial Areas
Situation and Nature of the Problem.—Vegetation must be controlled in industrial and com-
mercial areas for access, inspection, fire prevention and control, air circulation, corrosion control,
safety, and appearance. Industrial areas are quite diverse, and the level of vegetation control varies
with the nature, location, and use of the area. Vegetation-control practices in industrial areas may
be divided into classes based on the degree of control required: complete and partial or selective.
Situations requiring or commonly practicing complete control are (1) oil tank farms and re-
fineries, (2) electrical substations, (3) storage areas and pole yards, and (4) industrial railroad
sidings.
Situations requiring or commonly practicing partial or selective weed control are (1) parking
lots, (2) drive-in movies, and (3) sign posts and outdoor advertising sightlines.
Mechanical Control.—Vegetation can be completely controlled in industrial areas by hand
cutting or mowing; by bulldozing, blading, or scraping; and by controlled burning. In areas of sea-
sonal rainfall mechanical vegetation control is mainly required during the rainy season, although
some tall vegetation continues to grow during the dry or summer season. In areas of regular, non-
seasonal rainfall, vegetation must be controlled for the entire growing season. Since access to the
vegetation is often restricted by pipelines, structures, or stored materials, special implements are
often required. Costs for mechanical control vary from $40 to $200 per acre, depending on the size
of the area, nature of obstructions, climate, weather, and type of vegetation present. Burning can
*See Table 1.
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be used in some industrial areas but is impossible in refineries, petroleum-storage areas, and elec-
trical substations. It is impractical in many storage areas.
Chemical Control.*—Herbaceous weeds can be controlled by contact, translocated, or residual
herbicides—or a mixture of all three. Herbicide mixtures are most commonly used. The herbicide
mixture and rate are determined by the vegetation present and the degree of control needed. For
total weed control high rates of residual herbicides are often used, particularly in oil tank farms and
refineries. Where valuable woody vegetation is near the treated area, lower rates of residual herbi-
cides are used. They are generally combined with systemic herbicides to provide "knockdown" of
existing vegetation. Annual costs for chemical vegetation control range from $15 per acre in areas
of seasonal growth to $200 per acre in areas of high rainfall and long growing seasons.
Woody plants growing in industrial areas are usually controlled by one or more of the tech-
niques listed in the utility rights-of-way section. Where high rates of soil residual materials are used
for total vegetation control, woody plants are usually not a problem.
Perennial weeds like johnsongrass, dogbane, milkweed, or Canada thistle in industrial areas
may require spot treatment for satisfactory control. This technique requires less total herbicide on
the treated area since the control of annual vegetation requires relatively low rates of a residual
herbicide.
Potential Hazards.—Some potential hazards involved in weed control in industrial areas are the
following:
1. Injury to vegetation in adjacent untreated areas by surface runoff or leaching of herbicides
from rain or drainage water
2. Removal of cover and food plants for birds, rodents, and other wildlife
3. Increased erosion potential after vegetation removal
Ditch and Canal Banks
Ditches and canals are used for crop irrigation, stock watering, land drainage, transport, and
recreation. It is necessary to control the vegetation on the banks of these ditches and canals in
order to
1. Aid the flow of water for irrigation and drainage
2. Prevent or retard silt buildup in the ditch or canal by vegetation and refuse
3. Maintain access for maintenance and inspection
4. Prevent the spread of weed seed and plant parts by irrigation water and by wind and
animals to adjacent land areas
5. Control burrowing animals to aid in restriction of water loss
6. Reduce water use by phreatophytes (water-using plants)
It is generally necessary to maintain some type of vegetation on the bank to prevent erosion of
the bank. As a result, selective vegetation control methods are usually practiced.
*Specific herbicides for industrial vegetation control are listed in Table 1.
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Chemical Methods of Control.*—Since the water in the ditch or canal may be used for crop
irrigation, stock watering, fishing, swimming, and human consumption, any herbicides that are
applied to, or find their way into, the water must have established tolerances or be approved for use
by the appropriate agencies. Techniques that permit the application of herbicides to the banks with
a minimum of contamination of the water are important in ditch and canal bank spraying.
Woody Plants.—Woody plants on ditch and canal banks can be controlled by spray applications
of 2,4-D, dichlorprop, silvex, picloram, dicamba, bromacil, or karbutilate—or by granular or pellet
applications of picloram, bromacil, or karbutilate. 2,4,5-T may not be used on ditchbanks. Pic-
loram may not be applied to the inner bank or bottom of irrigation ditches since contamination of
water would result. Similar restrictions govern the use of the other herbicides. Ground applications
use equipment or techniques that limit the herbicide to the bank, although some small amount of
herbicide enters the water. Aerial applications on wide ditches are made to each ditchbank using
drift-control equipment or techniques that limit the amount of herbicide entering the water. On
narrow ditches both banks are often sprayed in one pass, with the aircraft centered over the ditch.
More herbicide enters the water on these single-pass applications.
To control scattered brush, the conventional brush-control techniques listed under the utility
rights-of-way section are often employed. Rates and volumes are similar to those reported in that
section.
Herbaceous Vegetation.— Annual broadleaf weeds on ditch and canal banks can be controlled
with a foliage spray of 2,4-D at rates of 1 to 4 Ib/acre. Ground or aerial application equipment may
be used, although ground equipment is most common where the bank is drivable. Application is
usually made before seedheads are formed.
Perennial broadleaf weeds on ditch and canal banks generally require spot treatment with her-
bicides like 2,4-D, dicamba, fenac, TEA, or picloram. Eradication of perennial weeds on irrigation
ditches is especially important to prevent the spread of noxious weed seeds or plant parts to
cropland.
Perennial grasses may either present a hazard to cropland, as with johnsongrass, or may actu-
ally obstruct the flow of water, as with reed canarygrass, phragmites, or cattail. Spot or strip treat-
ment with dalapon, amitrole-T, TCA, bromacil, or karbutilate is the general practice.
Mechanical Control.—Mowing or hand cutting of vegetation is possible on banks that are not
steep and can be driven. Rocks, large trees or stumps, and uneven terrain limit the use of mowers.
Trees and brush can be hand cut, subject to the limitations listed in the utility rights-of-way
section. Ditches that have become overgrown and silted in can be restored to full flow by draglining
or bulldozing.
DOMESTIC AND RECREATIONAL USES-
WEED CONTROL IN TURF
Introduction
Turf is defined as "the upper stratum of soil bound by grass and plant roots into a thick mat."
Grasses are the primary component of turf maintained intensively enough to require and justify
weed control. Because of their basal, rather than apical, growth, grasses grow thickly and withstand
constant clipping, providing a compact live cover that can be sustained indefinitely when handled
*See Table 1.
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properly. The primary turfgrasses in the northern cool-season area are Kentucky bluegrass (Poa
pratensis), Colonial and creeping bentgrasses (Agrostis spp.), and certain fescues (Festuca spp.). In
the southern warm-season belt Bermuda grass (Cyhodon dactylon), zoysia (Zoisia japonica), and St.
Augustine (Stenotaphrum secundatum) are most important. About a dozen other species are signifi-
cant locally, and scores of cultivars (cultivated varieties) have been selected for specific qualities.
The physical characteristics and growth requirements of grasses differ considerably and. deter-
mine their suitability as turf components for various conditions and purposes. In warm regions cer-
tain low-growing broadleaf plants are also used for turf. Chief among these are dichondra (Dichon-
dra repens) and lippia (Phyla nodiflora).
The basic turf goal is to establish and maintain a uniform dense stand of predetermined species
without unwanted grass or broadleaf species. Such a stand best performs the basic function of
stabilizing soil and minimizing movement of soil particles. The binding network of roots and
spreading runners controls erosion where water, wind, or wear would otherwise carry soil away.
Good turf does this more efficiently than other plants that might occupy the same area, whether in
the vast acreages of agricultural land and watersheds, along highways whose stability depends on a
firm base, or on sloping lawns. Turfgrasses trap and hold dust and mud around homes, schools, and
other public buildings and in playing fields, airfields, and similar installations, thus promoting health
and comfort.
Turf absorbs and reflects solar energy. It may cool air several degrees by transpiration and
evaporation, and in cool weather may prevent some heat loss from soil. It also reduces glare. The
clipped turf of home lawns, athletic fields, and golf courses absorbs shock and reduces the risk of
injury from falls. Turf is an excellent sound absorber, better than trees and shrubs because of its
great surface area and resilience.
Good turf is an important decorative element in the landscape, providing an attractive setting
for private or public buildings and natural or manmade ornaments. It adds spaciousness to outdoor
living space and appreciable value to real estate. Along highways and around airports and industrial
installations, turf provides safety as well as beauty, permits economical maintenance, and is an im-
portant element in soil conservation. Good turf is a basic part of multibillion-dollar sports activities
such as golf with their many satellite investments of land, buildings, equipment, and manpower.
Historically, clipped turf is probably the outgrowth of grazing to prevent regrowth of cleared
forests, and it continues to serve the same purpose in parks, historical sites, watershed areas, mili-
tary lands, and other similar large-area situations. From that practice the fine turf now desired and
necessary for many recreational purposes has gradually evolved.
Quality of turf may range from the open, informal populations of roadsides or meadows
(mowed perhaps two to four times a year and often including low, broadleaf plants) to the ultimate
of intensively groomed golf course putting greens with uniform fine grass daily mowed as close as
1/16 inch.
The greatest amount of turf is in home lawns, although other situations such as golf courses
have more exacting requirements and standards, and hence demand more intensive management
techniques. To establish a degree of perspective, comparative expenditures for annual maintenance
alone are shown in Table 1. Since the figures were compiled, turf areas requiring intensive manage-
ment (such as around condominiums, apartment houses, and industrial parks) have increased, and
wages and other costs have risen fairly uniformly. Turfgrass is now considered to be a $12 billion
industry.
Turfgrass culture reverses the usual concept of encouraging the ultimate size, flowering, and
fruiting development of individual plants by removing competition. Instead, good turf requires
169
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crowding many grass plants into a given area, thus deliberately increasing competition by promoting
vegetative growth. The degree of crowding depends largely on the type of turf to be developed.
Turfgrass populations may range from 200 plants per square foot in a lightly grazed pasture to
20,000 in a fine putting green. The resultant plants are smaller and weaker than they would be if
growing naturally. Thus a paradox of balancing the results of desirable competition with those of
cultural skills is created.
Weeds (any unwanted plants) constitute the principal problem in establishing and maintaining
good turf, far surpassing those of insects and diseases. Most weeds originate from seed or other re-
productive organs in the soil of the turfed area or are introduced from surrounding areas. Weed-seed
proliferation is enormous, and viability is usually notoriously long. A British study (Salisbury, 1961;
p. 328) showed that 84 percent of ragweed and broadleaf plantain seed was still viable after 21 years
of dormancy!
Turfgrass seed quality is regulated by federal and state laws. Purity, germination, percentage by
weight of all crop and weed seed; and name and frequency of any noxious weeds present must be
stated on the seed package.
Whether or not some plants, particularly certain grasses, are considered desirable or weedy may
depend on the locality, manageability, and intended use. For instance, Bermuda grass is a basic turf
component in the South, but may become an invasive nuisance farther north. Bentgrass, pampered
to make fine putting greens, is a major weed in lawns. In areas subject to heavy traffic and in states
with long, hot summers, tall fescue is eminently suitable, but it is obnoxious when mixed with finer
textured grasses in northern lawns.
Weeds in turf impose the disadvantages already enumerated in preceding sections. For in-
stance, crabgrass and dandelions compete for moisture, nutrients, and light. Plantains and garlic
require additional maintenance time and labor. There are also weeds with poisonous, irritating, or
other injurious characteristics, such as the spiny burs of sandspurs, and those that harbor insects and
diseases (e.g., chickweed). Turfgrasses are already under the stress of competition even when the
Table 1. NATIONAL ANNUAL TURFGRASS MAINTENANCE EXPENDITURES BY
SELECTED FACILITY1
Facility Annual national expenditure Percent of total
Airports $34,606,352 0.8
Cemeteries 363,366,704 8.4
Churches 25,954,764 0.6
Colleges and universities 17,303,176 0.4
Golf courses 237,918,674 5.5
Highways 471,511,556 10.9
Lawns, residential 3,002,101,097 69.4
Lawns, commercial 25,954,764 0.6
Parks, municipal 60,561,117 1.4
Schools, public 38,932,147 0.9
Miscellaneous2 47,583,735 1.1
Total 4,325,974,086 100.0
'Source: Nutter (1965).
2 Includes sod and seed production; municipal, state, and Federal government building lawns; state and
Federal parks; private school facilities; professional athletic facilities; and others. Very conservatively esti-
mated. For example, Florida alone grows approximately $10,000,000 worth of commercial sod yearly.
170
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major factors of climate, soil, and management are favorable. This can be further aggravated by
mechanical wear or other injury. Without proper care, aggressive weeds can quickly invade turf and
reduce or nullify its functional and aesthetic purposes. When turf is thin because of unfavorable
conditions, major weed invasion is inevitable, perpetuating a vicious cycle.
The competitive effects of weeds on crops have been determined numerically. For example, in
an Illinois turf-establishment study (Madison, 1971; p. 75), when crabgrass was controlled in the
planting, one-half to one-sixth as much grass seed was required to produce the same quality turf as
where there was no crabgrass control.
Methods of Weed Control
Cultural Control.—Weeds in turf are generally the result of its poor quality, not the prime
cause. Good quality is produced by proper preparation and management. This includes the
appropriate choice of turf components; proper use of water, fertilizer, and pest controls; proper
mowing practices; and avoidance of mechanical injury, including excessive wear. Proper application
of principles varies from site to site, and especially from warm-season to cool-season turfgrass situa-
tions.
After weeds already established in the turf have been eliminated, further invasion can be con-
trolled by providing proper nutrition, correcting inadequate or excessive drainage, aerating, and
modifying extreme soil acidity or alkalinity, in addition to improving any weed-encouraging im-
proper management practices, such as overwatering.
Where new turf is to be established, it is possible to induce some of the weed seed already in
the soil to germinate before the turfgrasses are seeded, although this is inefficient and usually unde-
sirable for other reasons. If perennial weeds (e.g., Canada thistle or quackgrass) are present, the area
must be fallowed for one or more entire season.
Sodding instead of seeding minimizes the weed population, but it is expensive since producing
good sod requires the practices already mentioned and some that follow.
Mechanical Control.—Mowing is the most common method of restraining weeds in turf, either
through repressing plants like mustards and pigweeds, which are unable to tolerate constant close
clipping, or by reducing seed production somewhat (a grass catcher should be used to remove
mowed seedheads). However, mowing cannot eliminate the many species that are able to persist or
produce seed at less than the cutting height. Many low-growing, mat-forming weeds (e.g., prostrate
spurges, chickweeds, or crabgrasses) are in this category. Cutting height influences the quality of
turf, the optimum varying with the grass species. Bluegrasses and fescues cut at less than 2 to 2.5
inches may die back, especially in hot dry weather, and allow weeds to invade. Conversely, bent-
grass and Bermuda grass resist weeds best when cut 1 inch or lower. When allowed to grow higher,
they tend to mat or to develop a loose, open growth that is subject to disease and subsequent weed
invasion.
In increasing order of quality produced, equipment includes scythes, rotary mowers, flail
mowers, sicklebar mowers, and reel mowers. Other related factors, such as mowing frequency and
removing clippings and other debris, also influence turf health and hence the weed population.
Hand weeding might be advisable if there are relatively few weeds. Nonrhizomatous weeds like
plantains or clump grasses can be eliminated by cutting below the crown. Hand weeding moderate or
heavy infestations is impractical. Even if the amount of time required could be justified, seedlings
and some other weed plants would inevitably be missed. It is just about impossible to remove creep-
ing stem-rooting weeds like chickweed or maturing crabgrass manually or mechanically. Repeated de-
foliation may weaken some coarse grasses such as quackgrass.
171
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Certain weeds resistant to other controls can be dug out and replaced by sod, especially if the
infested area is not too large. Care must be taken to dig deeply and widely enough to remove all
roots or stems capable of reproduction. Although grazing may be feasible for rough meadows or
pastures where animals can be restricted and their droppings and soil compaction tolerated, it is
unacceptable for any good turf.
Chemical Control.—Controlling weeds with chemicals has been attempted for centuries with
little success until recently. The discovery of highly efficient and economical compounds during the
last 30 years has afforded control that was formerly unattainable. Used properly, these materials
accomplish tasks that are impossible with cultural and mechanical techniques. The increasing short-
age and high cost of labor add to the importance of chemical weed control.
Herbicides may be selective, killing weeds but not the turfgrasses with which they are growing.
These materials have a systemic effect, disorganizing metabolic processes of susceptible species.
They may be absorbed by germinating seedlings—as in preemergence treatment for crabgrass con-
trol—or by expanded foliage—as in postemergence treatment of dandelions and many other weeds,
especially broadleaved (dicotyledonous) ones. Contact herbicides, which kill any tissue they touch,
are usually not selective. They are therefore useful where all vegetation is to be controlled, as in
renovation work. Nonselective herbicides may be needed for weeds that do not respond to selective
herbicides, such as muhlenbergia. Fumigants^volatile compounds applied to the soil—kill several
types of living organisms, diseases, and insects as well as weeds.
Herbicides are used in different ways: before planting to ensure a weed-free seedbed, in newly
seeded turf to minimize competition with emerging turfgrass seedlings, and in established turf to
prevent the emergence of weeds or eliminate those already present. The chemicals used most com-
monly for these purposes are listed in Table 2 together with important considerations concerning
their use.
The characteristics of a given compound may vary somewhat in different forms. For example,
an emulsifiable ester formulation provides better penetration; a water-soluble amine is essentially
nonvolatile. Liquid formulations are usually more efficient than granular forms of the same herbi-
cide, requiring only about half as much active ingredient for the same effect. Liquid formulations
affect plants more quickly and may also be dissipated sooner. They are harder than the more con-
spicuous granular formulations to apply accurately. Inaccurate equipment must be avoided in any
case. Compounds are usually applied singly but may be combined to control a wider range of spe-
cies in one operation.
Nearly all herbicides used for turf weed control have low mammalian toxicity and are readily
decomposed in soil. They do not pose serious hazards to nontarget organisms when used as offi-
cially recommended. Rates of herbicide movement and decomposition in soil depend strongly on
soil type, temperature, and moisture levels. The extent of leaching is retarded by organic matter and
clay concent. Any volatility or photodecomposition will vary with temperature, light intensity, or
method of application. Factors favoring soil microorganisms—organic matter, warmth, moisture-
help accelerate the rate of microbial decomposition of herbicides in soil.
The satisfactory application of herbicides requires careful adherence to specific directions.
Overdosing or underdosing will produce results different from those desired. Herbicides are in-
tended to alter or prevent the growth of certain plants. Care must always be taken to avoid uninten-
tionally injuring sensitive, desirable plants with drifting spray particles, careless practices, improper
choice of chemical, or contaminating equipment used for nonherbicidal compounds. "Control is
often simple; extermination may be expensive, ridiculous or impossible ... a dense vigorous turf
containing an occasional dandelion or crabgrass plant has weeds under control if weeds are few and
fail to increase from season to season" (Madison, 1971, p. 155).
172
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BIBLIOGRAPHY
Altom, J. D., 1967. Persistence of Picloram, Dicamba, and Four Phenoxy Herbicides in Soil and
Grass, M.S. thesis, Oklahoma State University, 61 pp.
Audus, L. J. (ed.), 1964. The Physiology and Biochemistry of Herbicides, Academic Press, London
and New York, 555 pp.
Bailey, J. B., and Swift, J. E., 1968. Pesticide Information and Safety Manual, University of Cali-
fornia at Berkeley, 147 pp.
Burr, R. (comp.), 1972. Oregon Weed Control Handbook, Oregon State University, Corvallis, Oreg.
156 pp.
Crafts, A. S., 1961. The Chemistry and Mode of Action of Herbicides, Interscience Publishers, New
York, 269 pp.
Crafts, A. S., and Robbins, W. W., 1962. Weed Control, 3rd ed., McGraw-Hill, New York, 660 pp.
DeBach, P. (ed.), 1964. Biological Control of Insect Pests and Weeds, Reinhold, New York, 844 pp.
Hanson, A. S., and Juska, F. V. (eds.), 1969. Turfgrass Science, American Society of Agronomy,
Madison, Wise., 715 pp.
Hayes, W. J., Jr., 1963. Clinical Handbook on Economic Poisons, Public Health Service Publication
No. 476, U.S. Government Printing Office, Washington, B.C., 144 pp.
Kearney, P. C., and Kaufman, D. D. (eds.), 1971. Degradation of Herbicides, Marcel Dekker, Inc.,
New York, 394 pp.
King, L. J., 1966. Weeds of the World. Biology and Control, Interscience Publishers, New York, 526
pp.
Klingman, G. C., 1961. Weed Control: A Science, John Wiley & Sons, New York, 421 pp.
Klingman, D. L., and Shaw, W. C., 1967. Using Phenoxy Herbicides Safely, U.S. Department of
Agriculture Farmers' Bulletin No. 2183, U.S. Government Printing Office, Washington, B.C.,
24pp.
Lehman, A. J., 1965. Summaries of Pesticide Toxicities, Association of Food and Brug Officials of
the United States, Topeka, Kansas, 128 pp.
Madison, J. H., 1971. Practical Turfgrass Management, Van Nostrand-Reinhold, New York, 466 pp.
Muzik, T. J., 1970. Weed Biology and Control, McGraw-Hill, New York, 273 pp.
Nutter, G. 1965. "Turfgrass Is a Four Billion Bollar Industry" Turf-grass Times, 1, 1, 4.
Pimentel, B., 1971. Ecological Effects of Pesticides on Non-target Species, Executive Office of the
President, Office of Science and Technology, Washington, B.C., 220 pp.
Salisbury, E., 1961. Weeds and Aliens, Collins, London, 384 pp.
Sax, N. I., 1968. Dangerous Properties of Industrial Materials, 3d ed., Reinhold, New York, 1251
P-
Upchurch, R. P., 1966. "Behavior of Herbicides in Soil," Residue Reviews, 16, 46.
Weed Science Society of America, 1970. Herbicide Handbook of the Weed Science Society of
America, W. F. Humphrey Press, Geneva, N.Y., 368 pp.
Wilkinson, R. E. (ed.), 1972. Research Methods in Weed Science—25th Anniversary Commemorative
Issue, Southern Weed Science Society, Experiment, Ga., 198 pp.
178
-------
APPENDICES
-------
Appendix I
STRUCTURE AND PHYSICAL PROPERTIES OF
SOME HERBICIDES
Solubility
Common name
Structure
Vapor pressure
mm Hg (°C)
... A
Water Acetone
Xylene (X) or
, ,„.
benzene (B)
Acrolein
Alachlor
CH2=CH-CHO
C2H5
325 (30) 25% Miscible Miscible (X)
0.02(100) 148 ppm Soluble Soluble (B)
C-CH2CI
C2H5
Cl
Atrazine
3X10~7(20)
1.4X10~6(30)
33 ppm
1.8g/100g 360 ppm
(methanol) (n-pentane)
Butylate
W
(CH3)2HCHN N NHC2H5
0 CH3
11 '
CH3-CH2-S-CN(CH2-CH-CH3)2 13X10~3(25) 45 ppm Miscible Miscible (X)
Chloramben
H2N ci
Cl
700 ppm 23 g/100 g 0.02 g/100 g (B)
Copper sulfate
CuSO4
Soluble
2,4-D
Cl
Cl—(' V-OCH2C^
6X10~7(25) 600-700 ppm 45 g/100 cc 1.07 g/100 cc (B)
Diuron
Cl
Cl
0.31 X 10~5 (50) 42ppm 5.3 g/100 g 0.12 g/100 g (B)
Endothall
10% 7 g/100 g 0.01 g/100 g (B)
Linuron
Cl
O
Jl
NHC-N
Cl
75 ppm 50g/100g 13g/100g(B)
180
-------
STRUCTURE AND PHYSICAL PROPERTIES OF SOME HERBICIDES-Continued
Common name
Structure
Vapor pressure
mm Hg (°C)
Water
Solubility
Acetone
Xylene (X) or
benzene (B)
Nitralin
NO2
N(C3H7)2
NO2
<1.5X 1CT6 (25) 0.6 ppm 37g/100g <12.5 g/100 g (B)
Propachlor
CH2CI
0.03(110) 700 ppm 30.9% 50% (B)
Cl
Propazine jj
(CH3)2HCHN N"
2.9X10~8(20) 8.6 ppm Differs diff. (X, B)
Trifluralin
N02
N(C3H7)2
NO2
1.99X 10~4 (29.5) < 1 ppm
1.19
1.73 (X)
(% molarity) (% molarity)
Xylene
CH^
Q-
-CH3
Isomer:
o
m
P
6.62
8.30
8.76
(25)
(25)
(25)
196
198
ppm
ppm
Miscible
Miscible
Miscible
Miscible
Miscible
Miscible
(B)
(B)
(B)
Source: Table prepared by E. E. Kenaga, July 1972.
181
-------
Appendix II
GLOSSARY
Accumulation. See Bioconcentration.
Biennial. A plant that requires two growing seasons to go from seed to seed.
Bioaccumulation. Uptake and retention of environmental substances by an organism from its
environment, as opposed to uptake of food.
Bioassay. A determination of the concentration or dose of a given material necessary to
affect a test organism under stated conditions.
Bioconcentration. Action of a living organism in absorbing and retaining a foreign substance
so that there is more in the organism than in the environment.
Biotransformation. Action of an organism in altering a foreign chemical compound.
Broadcast (blanket) application. An application of spray or dust over an entire area rather
than only on rows, beds, or middles.
Carryover. Pesticide remaining from previous seasons.
Chromatography. Process of separating chemical compounds by allowing a solution to seep
through an adsorbent (e.g., clay or paper) so that each compound becomes adsorbed in a separate
layer.
Colorimetry. Technique of chemical analysis based on comparing a liquid's color with standard
colors.
Cometabolism. Alteration of a chemical by an organism occurring only when a second com-
pound is available as an energy source.
Condensate (or conjugate). Metabolite formed by joining pesticide molecule with molecule of
another substance, e.g., glucuronic acid.
Degradation. Breakdown of a pesticide to other chemical species usually of simple structure.
Degradation product. Chemical species produced from applied pesticide, usually simple in
structure.
Derivative chemical. Chemical formed from another for identification or for easier separation.
182
-------
Directed spray. An application made to minimize the amount of herbicide applied to the
crop. This is usually accomplished by setting nozzles low with spray patterns intersecting at the
base of the plants just above the soil line.
Edema. Swelling.
Filamentous (algae). Threadlike.
Food chain. The transfer of food energy from plants or organic detritus through a series of
organisms, usually four or five, consuming and being consumed.
Formulation. Physical and chemical form of pesticide prepared for specific use, e.g., emulsion
granules.
Functional group. A characteristic reactive unit of a chemical compound.
Halogen. Any of the four elements fluorine, chlorine, bromine, and iodine.
Herbaceous plant. A vascular plant having little or no woody tissues.
Herbicide. A chemical used for killing or inhibiting the growth of plants.
Histology. A branch of anatomy that deals with the minute structure of animal and plant
tissues as discernible with the microscope.
Hydrolysis. Chemical process of decomposition involving the splitting of a chemical bond and
addition of the elements of water.
Incorporation in soil. Mixing of the herbicide with the soil, usually by mechanical means.
Isomeric. Chemical compounds having the same number of each atom but arranged differently.
Isotomic solutions. Solutions of equal osmotic strength.
LC50 (median lethal concentration). The concentration of a test material that causes death to
50 percent of a group of test organisms.
LD50 (median lethal dose). The dose of a test material, ingested or injected, that kills 50 per-
cent of a group of test organisms.
Leach. Usually refers to percolating of water through a soil, which may move soluble compo-
nents, such as chemicals or minerals.
Mass spectrometry. Technique for separating a stream of charged particles into groups accord-
ing to the ratio of their charge to their mass.
Metabolism (of a pesticide). See Biotransformation.
Metabolite. New chemical species formed by biological action.
Microcoulometry. Technique of chemical analysis based on determining the amount of a sub-
stance released in an electrolysis.
183
-------
Molluscicide. An agent, such as a chemical, for killing mollusks (e.g., pesticide).
Perennial. A plant that continues to live from year to year, renewing top growth seasonally or
dying back seasonally and producing new growth.
Persistent pesticide. One that is destroyed only slowly by natural processes.
Photolytic (breakdown product). Of or relating to the formation of a chemical from another
chemical by the action of light.
Photosensitizer. Chemical that causes light to have a harmful effect on a living organism.
Phytotoxic. Pertaining to or describing a substance poisonous to plants.
Phytotoxicant. Plant poison.
Phytotoxin. A poison derived from a plant.
Picogram. One-trillionth of a gram.
Plant pathogens. Agents, usually living, capable of producing diseases in plants.
Polarography. Method of analysis based on current-voltage curves obtained during the elec-
trolysis of a solution with a steadily increasing electromotive force.
Postemergence. After emergence of a specified weed or crop.
Preemergence treatment. Treatment made after a crop is planted but before it emerges.
Preplanting treatment. Treatment made before the crop is planted.
Pyrolysis. Breakdown of molecules by heat.
P-value. Partition coefficient ratio of solubilities in two immiscible liquids.
Radiolabeling. Synthesis of compounds containing a radioactive isotope to permit tracing by
radiation-detection equipment.
Reagent. Substance used in detecting or measuring a compound or preparing a compound be-
cause of its chemical activity.
Residues. That which remains after a part has been removed, taken, or separated.
Selective. Affecting some species much more than others.
Selective herbicide. A compound that is more toxic to the weeds than to the crop in the field.
Soil sterilant. Chemical capable of killing every living thing in the soil.
Spectrophotometry. Technique for measuring the relative intensities of the light at different
wavelengths.
Spot treatment. Application of sprays to localized or restricted areas, as differentiated from
broadcast coverage.
184
-------
Spray drift. The movement of airborne spray particles from the spray nozzle beyond the in-
tended contact area.
Synthesis. Making a chemical from simple chemicals.
Target species. Plant species to be destroyed.
Tolerant. Withstanding the action of a substance (e.g., pesticide) or condition without harm.
Translocation. Movement or transfer of a substance (e.g., chemical) from one location to
another location within a plant.
Vapor drift. The movement of vapors from the area of application to other areas.
Weed. A plant growing where it is not desired.
185
-------
Appendix III
COMMON AND CHEMICAL NAMES OF HERBICIDES3*
Common Name or Designation
Chemical Nameb
acetochlor (a se' to klor)
acrolein (a kro'le in)
alachlor (aTa chlor)
ametryn (am'S trm)
amiben (see chloramben)
amitrole (am'i trol)
AMS
asulam (as' u lam)
atraton (a'trd ton)
atrazine (a'trd zen)
barban (bar'ban^
benefin (ben'S fin)
bensulide (ben'sul id)
bentazon (ben'ta zon)
benthiocarb (ben thi o carb)
benzadox (ben'zuh dox)
benzipram ('ben zi pram)
bifenox (b" fe nak§)
bromacil (bro'ma sil)
bromoxynil (bro mox'y nil)
butachlor (by'u t' a klor)
butam (bju' taam)
butralm (bu' tra lin)
buturon (bil'tu ron)
butylate (bu'ti lat)
cacodylic acid (ca'co dyl'ic)
carbetamide (car bet' a mide)
CDAA
CDF.C
chloramben (klor am'ben)
chlorazine (klo' til 7en)
chlorbromuron (klor' brom u ron)
chloroxuron (klo rdx'ii ron)
chlorpropham (clor pro fam)
CIPC (see chlorpropham
CMA
cyanazine (ci-an'-a-zen)
cycloate (sy'_clo at)
cycluron (sy'klu ron)
cyperquat ( si par kwat)
cypra?me (sfprS zeen)
cyprazole (si' pra zol)
cypromid (sy'pro mid)
dalapon (dal'a pon)
dazomet (da'zo met)
DCHA
DCU
delachlor (del a klor')
desmedipham (dez' med 5 fam)
desmetryn (des'm8 trin)
diallate (di'al lat)
dicamba (di kiim'ba)
dichlobeni! (di'clo ben'il)
dichlormate (di chlor mate)
dichlorprop (di'clor prop)
dicryl (df cril)
difen/oquat (di 'fen zo kwat)
dinitramine (di-ni'-tra-men)
dinosam (d^no sam)
dinoseb (dl'no seb)
diphenamid (di fen' a mid)
dipropetryn (di' prop' & tryn)
diquat (dTkwat)
diuron (di"u ron)
DMTT (see dazomet)
DNAF (see dinosam)
DNBP (see dinoseb)
DNC (see DNOC)
*From Weed Science, 22. No. 2, March 1974; reprinted by permission of Weed Science Society of America, 113 N. Neil St.,
Champaign, III. 61820.
2-chloro-/V(ethoxymethyl)-6 -ethyl-o-acetotoluidide
acrolein
2-chloro-2',6'-diethyl-iV-(methoxymethyl)acetamllde
2-(ethylamino)-4-(i50propylamino)-6-(methylthio)-j-triazme
3-amino-s-tnazole
ammonium sulfamate
methyl sulfamlylcarbamate
2-(ethylamino)-4-(isopropylarmno)-6-methoxy-s-tnazine
2-chloro-4-(ethylammo)-6-(isopropylamino)-j-triazine
4-chloro-2-butynyl m-chlorocarbanilate
/V-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine
O,O-diisopropyl phosphorodithioate 5-ester with /V-(2-mercaptoethyl)ben?enesulfonamide
3-isopropyl-lf/-2,l,3-benzothiadiazin-(4)3//-one 2,2-dioxide
5-((4-chlorophenyl)methyl | diethylcarbamothioate
(benzamidooxy)acetic acid
N-benzyl-N-isopropyl^^-dimethylbenzamide
methyl S-(2,4-dichlorophenoxy)-2-nitrobenzoate
5-bromo-3-sec-butyl-6-methyluracil
3,5-d:bromo-4-hydroxybenzonitnle
W-(butoxymethyl)-2-chIoro-2',6'-diethylacetanihde
2,2-dimethyl-^V-(l-methylethyl)-AL(phenylmethyl)propanamide
4-(l,l-dimethyiethyl) -(l-methylpropyl)-2,6-dmitroben7enamme
3-(p-chlorophenyl)- 1-n.ethyl- l-(l-methyl-2-propyny!)urea
S-ethyl dnsobutylthiocarbamate
hydroxydimethylarsme oxide
D-yV-ethyllactamidf carbamlate (ester)
N,A'-diallyl-2-chloroacetamide
2-chloroallyl diethyldithiocarbamate
3-amino-2,5-dichloroben7oic acid
2-chloro-4,6-bis(diethylamino)-5-tna7ine
3-(4-bromo-3-chloropheny I )-l-methoxy-l-methyl urea
3-|p-(p-chlorophenoxy)phenyl|-l,l-dimethylurea
isopropyl m-chlorocarbamlate
calcium methanearsonate
2-1 [4-chloro-6-(ethylamino)-s-tna7in-2-yl j amino ] -2-methylpropiomtrile
S-ethyl N-ethylthiocyclohexanecarbamate
3-cyclooctyl-l ,1-dimethylurea
l-methyl-4-phenylpyridimum
2-chloro-4-(cyclopropylamino)-6-(isopropylamino)-J-tnazine
N-\ 5-(2-chloro-l, I dimethylethyl)-1,3,4-thiadiazol-2-yl ] cyclopropanecarboxamide
3',4'-dichlorocyclopropanecarboxanihde
2,2-dichloropropiomc acid
tetrahydro-3,5-dimethyl-2//-1,3,S-thiadiazme-2-thione
dimethyl tetrachloroterephthalate
1,3-bis(2,2,2-trichloro- l-hydroxyethyl)urea
2-chloro-Ar-(isobutoxymethyl)-2',6'-acetoxyhdide
ethyl m-hydroxycarbamlate carbamlate (ester)
2-(isopropylammo)-4-(methylamino)-6-(methylthio)-5-tnazine
S-(2,3-dichloroallyl)dnsopropylthiocarbamate
3,6-dichloro-o-amsic acid
2,6-dichlorobenzonitrile
3,4-dichlorobenzyl methylcarbamate
2-(2,4-dichlorophenoxy)propiomc acid
3',4'-dichloro-2-methylacrylamlide
l,2-dimethyl-3,5-diphenyl-l//-pyrazohum
Af<,Af4-diethyl-oi,Q,a-trifluoro-3,5-dinitrotoluene-2,4-diamine
2-(l-methylbutyl)-4,6-dinitrophenol
2-sec-butyl-4,6-dinitrophenol
/V,Af-dimethyl-2,2-diphenylacetamide
2-(ethylthio)-4,6-bis(isopropylamino)-^-triazine
6,7-dihydrodipyrido| l,2-a'2',l' c\ pyrazmediium ion
3-(3,4-dichlorophenyl)-1,1-dimethylurea
186
-------
DNOC
DSMA
endothall (en'do thai)
EPTC
erbon (ur'bon)
ethiolate (e thl' 6 late)
EXD
fenac (fen'ac)
fenuron (fen'ii ron)
fenuronTCA
fluchloralm (flu klor' a lin)
fluometuron (flii 6 met'u ron)
fluorodifen (flur 6 di'fen)
glyphosate (glTfo sat)
HCA
hexaflurate (hex' a floor'ate)
loxynil (i ox'y nil)
ipazine (fp' tt zen)
IPC (see propham)
isocil (i'so sil)
isopropalin (i'sopro'pa lin)
karbutilate (kar by'ut'l at)
KOCN
lenacil (len' A cil)
linuron (lin'ii ron)
MAA
MAMA
MCPA
MCPB
MCPES
MCPP (see mecoprop)
mecoprop (mec'6 prop)
metham (meth'am)
methazole (meth'-a-zol)
metobromuron (met'6 brom'u ron)
metribuzin (me-tn-bu'-zin)
MH
molmate (mo'h nat)
monolmuron (mon'o lin'ii ron)
monuron (mon'u ron)
monuronTCA
MSMA
napropamide (na prop' a mide)
naptalam (nap'ta lam)
neburon (neb'u ron)
nitralm (ni'trti lin)
nitrofen (ni'tro fen)
norea (no re'uh)
norflura/on (nor' fliir a /an)
NPA (see naptalam)
ory/aJin (6 n ta lin)
oxadiu7on (ox a di u zon)
paraquat (par' a kwat)
PBA
PCP
pebulate (peb'u lat)
perfluidone (per' flu i don)
phenmedipham (fen med'i fam)
picloram (pTc'lor am)
PMA
procyazme (pro 'si a 7en)
profluralm (pro fliir' a lin)
prometon (pro'mB ton)
prometryn (pro'me trm)
pronamide (pron' a mide)
propachlor (pro'pd clor)
propanil (pro'pa nil)
propazine (pro'pd zen)
propham (pro' fam)
prynachlor (prin' a klor)
pyrazon (pfrd /on)
pynclor (pi'n clor)
sesone (ses'on)
siduron (sid'u ron)
silvex (sil'veks)
simazine (sim'a zen)
simeton (sim'e ton)
simetryn (sim'e tnn)
SMDC (see metham)
solan (so'lan)
swep (swep)
4,6-dimtro-o-cresol
disodium methanearsonate
7-oxabicyclo|2.2.1 ]heptane-2,3-dicarboxylic acid
S-ethyl dipropylthiocarbamate
2-(2,4,5-tnchlorophenoxy)ethyl 2,2-dichloropropionate
S-ethyl diethylthiocarbamate
O,O-diethyl dithiobis[ thioformate |
(2,3,6-tnchlorophenyl)acetic acid
l,l-dimethyl-3-phenylurea
1,1 -dimethyl-3-phenylurea mono(trichloroacetate)
A'-(2-chloroethyl)-2,6-dinitro-/V-propyl-4-(trifluoromethyl)aniline
l,l-dimethyl-3-(a,Q,a-tnfluoro-m-tolyl)urea
p-nitrophenyl a,Q,a-trifluoro-2-mtro-p-tolyl ether
7V-(phosphonomethyl)glycine
l,l,l,3,3,3-hexachloro-2-propanone
potassium hexafluoroarsenate
4-hydroxy-3,5-diiodobenzonitrile
2-chloro-4-(diethylamino)-6-(isopropylammo)-j-triazine
5-bromo-3-isopropyl-6-methyluracil
2,6-dimtro-A',Ar-dipropylcumidine
ferf-butylcarbamic acid ester with 3-(m-hydroxyphenyl)-l
potassium cyanate
-dimethylurea
3-cyclohexyl-6,7-dihydro-lH-cyclopentapyrimidine-2,4(3f/,S//)-dione
3-(3,4-dichlorophenyl)- 1-methoxy-l-methylurea
methanearsonic acid
monoammomum methanearsonate
[(4-chloro-o-tolyl)oxy | acetic acid
4-|(4-chloro-o-tolyl)oxy] butyric acid
2-| (4-chloro-o-tolyl)oxy ] ethyl sodium sulfate
2-[(4-chloro-o-tolyl)oxy ] propiomc acid
sodium methyldithiocarbamate
2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadia7olidine-3,5-dione
3-(p-bromopheny I)-1-methoxy-l-methylurea
4-amino-6-ferf-butyl-3-(methylthio)-as-tnazine-5(4H)one
l,2-dihydro-3,6-pyndazmedione
5-ethyl hexahydro- l//-azepme- 1-carbothioate
3-(p-chloropheny!)-l-methoxy-I-methylurea
3-(p-chloropheny I)-1,1-dimethylurea
3-(p-chlorophenyl)-l ,1-dimethylurea mono(trichloroacetate)
monosodium methanearsonate
2-(a-naphthoxy)-,V,A'-diethylpropionamide
Ml-naphthylphthdlamu acid
l-hutyl-3-(3,4-dichlorophenyl)-l-methylurea
4-(methylsulfonyl)-2,6-dimtro /V,/V-dipropyUniline
2,4-dichlorophenyl-p-mtrophenylether
3-(hexahydro-4,7-methanomdan-5-yl)-1,1-dimethylurea
4-thl()ro-5-(methylamin<))-2-(a,a,or-tnfluoro-(n-tolyl)-3(2W)-pyrida/iii(>ne
3,5-dimtro-Ar' .A'4 -dipropylsulfamlamide
2-f?rr-butyl-4-(2,4-dichloro-5-isopropoxyplienyl)-AI-l,3,4-oxadiazolin-5-one
l,r-dimethyl-4,4'-hipyndinium ion
chlorinated hen/oic acid
pentachlorophenol
5-prop> I butylethylthiocarbamate
l,l,l-tnnuoro-.V-(2-methyl-4-(phenysulfonyl)phenyl| methanesulfonamide
methyl m-hydroxycarbamlate m-methylcarbanilate
4-amino-3,5,6-tnchloropicolinic acid
(acetato) phenylmercury
2-| | 4-chlor(>-6-((.yLlopropyldmmo)-1,3,5-trijzine-2-yl 1 ammo | -2-methylpropanemtrile
yV-fcycJopropylmethyl)-a,a.o-tnfluoro-2,6-dinitro-7V-propyl-p-toluidine
2,4-his(isopropylamino)-6-methoxy-5-tria/me
3,4-his(lsopropyldmino)-6-(methylthio)-^-tna/me
3,5-dichloro-A'-( 1,1-dimethyl-2-propynyl)benzamide
2-chloro-/V-isopropylacetamlide
3',4'-dichloropropionanihde
2-chloro-4,6-his(isopropylamino)-.?-trid7ine
isopropyl cdrhamlate
2-chloro-/V-0-methyl-2-propynyl)dcetanilide
S-amino-4-chloro-2-phenyl-3(2//)-pyrida7inone
2,3,5-tri(-hloro-4-py ndmol
2-(2,4-dichlorophenoxy)ethyl sodium sulfate
l-(2-methylcyclohexyl)-3-phenylurea
2-(2,4,S trichlorophenoxy)propiomt acid
2-chloro-4,6-his(ethylamino)-j-tna/me
2,4-bis(ethylamino)-6-methoxy-j-tria7ine
2,4-bis(ethylamino)-6-(methylthio)-i-tnazine
3'-chloro-2-methyl-p-valerotoluidide
methyl 3,4-dichlorocarbamlate
187
-------
tebuthiuron (leb u th" u r6n)
terbacil (ter'bd ell)
terbuthylazine (ter byu thil a zen)
terbutol (ter'bu t61)_
terbutryn (ter'bu trin)
TCA
triallute (trf al lap
tricamba (tri cam'bd)
Triclopyr ('tri klo pir)
trielazine (Iri It' & zen)
trifluralin (tri fliir' a Im)
trimeturon (tri m6t' u r6n)
2,3,6-TBAc
2.4-D
2,4-DB
2,4-DEB
2,4-DEP
2,4-DP (see dichlorprop)
2,4,5-T
2,4,S-TES
vernolate (ver'nu lat)
Af-|5-(l,l-dimethylethyl)-l,3,4-thiadiazol-2-yl|-A/,yv'-dimethylurea
3-ferf-butyl-5-chloro-6-methyluracil
2-(rerf-butylamino)-4-chloro-6-(ethylamino)-j-triazine
2,6-di-rcrf-butyl-p-tolyl methylcarbamate
2-(rcr/-butylamino)-4-(ethyiamino)-6-(methylthio)-j-tria7ine
trichloroacetic acid
5-(2,3,3-trichloroa!ly1)diisopropylthiocarbamate
3,5,6-trichloro-o-anisic acid
|(3,S,6-trichloro-2-pyridmly)oxy |acetic acid
2-chloro-4-(diethylamino)-6-(ethylamino)-s-tria?ine
Qf,Q,c<-trifluoro-2,6-dinitro-A',Af-dipropyl-p-toluidine
l-(p-chlorophenyl)-2,3,3-trimethylpseudourea
2,3,6-trichIoroben7oic acid
(2,4-dichlorophenoxy)acetic acid
4-(2,4-dichlorophenoxy)butyric acid
2-(2,4-dichlorophenoxy)ethyl benzoate
tris[ 2-(2,4-dichlorophenoxy)ethyl | phosphite
(2,4,S-tnchlorophenoxy)acetic acid
sodium 2-(2,4,S-tnchlorophenoxy)ethyl sulfate
S-propyl dipropylthiocarbamale
"Herbicides no longer in use in USA are omitted. Complete listing,
including these, is in WEEDS 14(4), 1966.
cThis herbicide usually is available as mixed isomers. When possible,
the isomers should be identified, the amount of each isomer in the
bAs tubulated in this paper, a chemical name occupying two lines ..mixture specified and the source of the experimental chemicals given.
separated by an equal (=) sign is joined together without any separation
if written on one line.
188
-------
INDEX
Acrolein, 3, 5, 13, 14, 50, 59, 69, 117-119, 127,
132, 180, 186
Acute toxicity. See Toxicity, acute.
Additives for herbicides:
Environmental impact, role in, 49
Foam additives, 49
Oil emulsifiers, 49
Thickeners, 49
Use of additives, 49
Viscosity additives, 49
Adsorption chromatography, 38
Affinity detector, 39
Agricultural uses of herbicides, 7, 8, 9, 75-78
Alachlor, 3, 16, 50, 58, 180, 186
Algae, 112, 115, 118
Aliphatic acids, chlorinated, 3, 28
Allelopathy, 136
Alligatorweed, 116, 124
Amiben (chloramben). See Chloramben.
Amides, 3, 18, 26, 27
Amitrole, 87, 88, 128, 161, 173, 186
Amount of use of herbicides, 66
Application methods of herbicides:
Forestry, techniques, in, 90
Grain crops, improved application methods for,
155
Aqualin (acrolein). See Acrolein.
Aquatic vegetation. See also Weeds, aquatic, under
chemical control.
Activities affected by aquatic weeds, 113-115
Advantages and disadvantages of chemical
control of aquatic weeds, 123, 124
Biological weed control, 122, 123
Characteristics of aquatic weeds, 112, 113
Control of aquatic weeds, 8, 59, 60, 115-117,
133
Economic impact of restricting use of aquatic
herbicides, 133, 134
Economics of aquatic weed control, 69
Effectiveness of aquatic weed control, 69
Environmental consequences of herbicide use,
124-133
Eutrophication, important reason for increased
aquatic weed problems, 70
Fisheries, management of, 114
Herbicides, 115-121
Irrigation agriculture, 113
Mechanical control of aquatic weeds, 121-123
Navigation, 115
Pollution from aquatic weed control, 70
Property values, 114
Recreation, 113
Resources affected by aquatic weeds, 113-115
Social impact of restricting the use of aquatic
herbicides, 133-134
Training requirements for herbicide use, 134
Types of aquatic weeds, 112, 113
Water supplies (potable water), 115
Weeds, aquatic, 112, 113
Weeds, aquatic, under chemical control, 115-
121
Wildlife management, 114
Areas of use of herbicides:
Aquatic areas, 112-134
Domestic areas, 168-177
Forests, 77-92
Fruit crops, 151-153
Grazing lands, 93-110
Industrial sites, 158-168
Nut crops, 151-153
Pastures, 104-110
Recreational areas, 168-177
Row crops, 145-150
Solid-seeded crops, 153-157
Aromatic compounds, chlorinated, 18
Aromatic solvents, 117, 118, 127, 130
Arsenicals, 3, 32, 33
Atomic absorption, use of, to detect residues of
herbicides, 40
Atrazine:
Amount of use, 65
Classification, chemical, 15
Crop rotation, interference with, 46
Crops that atrazine is used with 65, 146
Forestry, use in, 87-89
Grasses, use with, 103
Grasses, weed, control of, 103
Industrial use, 161
Name, chemical, 3, 13, 186
Persistence in soil, 58
Properties, 21, 180
Residue, 5, 57, 58
Selective nature, 103, 146
Structure, 180
Toxicity, acute, 50
Toxicity to animals, 50
Turf, use with, 173
Used most widely, 64
Year of initial use, 13
Atrex (atrazine). See Atrazine.
Azobenzenes, 17, 18, 41
B
Banks of canals and ditches, chemical weed control
on, 168
Banks of canals and ditches, mechanical weed control
on, 168
Benefin, 156, 186
Bentgrass, 105, 169, 173, 176
Bentgrass, Colonial, 105
Benzoic acids, chlorinated, 3, 29
Bermuda grass, 169, 170, 175, 176
Bioaccumulation, 4, 56, 182
Bioconcentration, 4, 56, 182
189
-------
Biological weed control:
Aquatic areas, 122, 123
Crops, 142, 143
Forests, 84
Grazing lands, 101
Biomagnification, 48, 56
Biotransformation, 182
Bipyridiums, 31, 32
Bluegrass, 102, 169, 174, 175
Broadcast application:
Aerial spraying, 160
Definition, 182
Dormant-cane treatment, 160
Forestry, use in, 90
Industrial and urban sites, use on, 159, 160
Broadleaf herbaceous weeds, 103, 121, 140, 144,
149,154, 156, 172-174, 175
Broadleaf herbaceous weeds, control of, 103
Bromacil, 161, 164, 168, 186
Brown and burn technique, 83
Brush control, results of, 97
Brush, individual stem treatments of, with herbicides:
Basal-stem treatment, 98
Cut-stump treatment, 99
Frill or tree injection, 99
Bulldozing, 7, 108, 166
Butylate:
Classification, 16
Name, chemical, 3, 14
Persistence in soil, 58
Properties, 25, 180
Structure, 180
Toxicity, acute, 50
Toxicity to animals, 50
Year of initial use, 14
Chokecherry, 103
Chromatography:
Adsorption Chromatography, 38
Definition of Chromatography, 182
Gas-liquid Chromatography, 38-39, 40, 42
Pyrolytic gas-liquid Chromatography, 41
Thin-layer Chromatography, 41, 42
Two-dimensional thin-layer Chromatography,
41
Chronology of herbicides introduced after 1950, 13,
14
Classes, chemical, of herbicides, 15, 16
Classification, chemical, of herbicides, 12, 14-18
Colorimetry, 39, 40, 182
Cometabolism, 182
Communication lines, 158
Contamination of herbicides, 33, 34
Copper sulfate, 3, 5, 11, 51, 59, 115, 116, 118, 119,
124, 127, 129, 133, 180
Crabgrass, 102, 146, 170, 172, 173, 176
Creosotebush, 100
Crested wheatgrass, 102
Crops:
Fruit crops, 151-153
Herbicides used with crops, role and effects
discussed, 137, 138
Minor acreage crops, 152-154
Nut crops, 151-153
Row crops, 140-150
Solid-seeded annual crops, 153-155
Solid-seeded perennial crops, 155-158
Weed effects on crops, 136-137
Curly dock, 105
Cutrine, 116
Canada thistle, 103, 105, 142, 167, 171
Canal and ditch banks, chemical weed control, 168
Canal and ditch banks, mechanical weed control, 168
Carbamates, 3, 15, 18, 22-24, 39, 56, 88
Chemical classification of herbicides, basis of, 12,14-18
Chemical structure of herbicides, 180, 181
Chemical weed control:
Ditch and canal banks, 168
Industrial sites, 159-163
Row crops, weed control in, 144-150
Turf, weeds in, 172
Urban sites, 159-163
Chemistry of herbicides:
Classification, chemical, basis of, 12, 14-18
Contamination, 33, 34
History of herbicides (before 1970), chemicals
used, 11, 12
Metabolism, herbicide, 34, 35
Names, chemical, of herbicides, 186-188
Properties, chemical, of herbicides, 18-33
Structure, chemical, of herbicides, 180, 181
Chickweed, 105
Chloramben:
Name, chemical, 3, 13, 186
Structure, chemical, 180
Toxicity, acute, 51
Toxicity to animals, 51
Year of initial use (Amiben), 13
DCA (dichloroaniline), 17
DDT, 4, 56, 57, 60
Dalapon, 28, 87, 102, 121, 124, 129, 152, 157, 161,
'174,186
Deathcamas, 103
Decomposition of herbicides in turfs, 172-177
Degradation of herbicides, 34, 182
Derivatization, 41
Detoxication, 35
Detrimental effects of herbicides used in row crops,
145
Dichlobenil, 5, 13, 16, 28, 29, 56, 116, 119, 127,
128, 130, 186
Dichlone, 116, 132
Dichloroaniline (DCA), 17
Dichlorophenoxyacetic acid—2,4-Dichlorophenoxy-
acetic acid (2,4-D):
Amount of use, 65, 66
Application rates, 127
Aquatic vegetation, use for, 59, 69, 116, 120,
121, 127-130
Bioconcentration, 4, 56
Classification, chemical, 15
Contamination, 33, 34
Corn, one of most used herbicides for, 2
Crop production increased with use, 76
Degradation, 35
Economic advantage, 9, 137
190
-------
Environment, effects on, 49, 51, 56, 61, 66
Exports, 20
Feed, animal, levels in, 57
Food, levels in, 57
Forestry, use in, 88-90
Fruit crops, use with, 152, 154
Grazing lands, use with, 97, 98, 103, 106-110
Industrial use, 159, 161, 163, 168
Lack of supply, 20
Levels in food and animal feed, 57
Metabolism, 56
Modern herbicide, 12
Movement in environment, 49
Name, chemical, 3, 188
Nut crops, use with, 152, 154
Pastures, use with, 106-110
Persistence, 58
Pest increase because of use, 6, 61, 62, 66
Pollutants in air, interaction with, 61
Production, amount of, 2, 20
Properties, 19
Residues in air, 60
Residues in soil, 57-59
Residues in water, 5, 58, 59, 128, 129
Resistance of plants to pests lowered by use, 6,
61,66
Row crops, use with, 144, 149
Solid-seeded perennial crops, use with, 157
Structure, 180
Sunlight, effects by, 60
Synthesis, 18
Toxicity, acute, 51
Toxicity to animals, 51
Turfs, use with, 175
Urban use, 159, 163
Vaporization, 49, 66
Dichondra, 169, 173
Dinitroanilines, 30, 31
Dioxins, 2, 17
Diquat, 5, 13, 16, 32, 62, 116-119, 127, 128, 186
Diseases to crop plants from herbicide use, 61, 62, 66
Dissipation of herbicides in water, 127-130
Ditch and canal banks, chemical weed control, 168
Ditch and canal banks, mechanical weed control,
168
Diuron:
Aquatic weeds, control of, by diuron, 69
Bioconcentration, 4, 56
Environment, effects on, 52
Fish, residues in, 130
Industrial use, 161
Irrigation, use in, 118
Life, when used with solid-seeded annual crops,
154
Name, chemical, 3, 13, 186
Production, estimated, 22
Properties, 23
Residues, 57, 59, 130
Solid-seeded annual crops, use with, 154
Solid-seeded perennial crops, use with, 157
Structure, 180
Toxicity, acute, 52
Toxicity to animals, 52
Year of initial use, 13
Downy brome, 101, 102, 153
Drift, 48, 49
Duckweed, 117
Ecological effects of herbicides, 6, 7, 45-48, 60-64,
66-70
Economics of weed control:
Aquatic areas, 69, 113-115, 122, 133, 134
Corn, 64
Crops, 64, 137, 138, 140, 141, 151
Domestic and recreational areas, 170
Forests, 79
Grazing lands, 94, 107-110
Industrial areas, 68, 69, 160, 163-167
Turfgrass maintenance, 170
Urban areas, 159, 160, 163-167
Electric distribution lines, weed problems with, 158
Electric transmission lines, weed problems with, 158
Electrolytic conductivity detector, 39
Electron-capture detector, 39
Emersed plants, 113, 120
Endothall:
Algae, use to eliminate, 116
Aquatic weed control, 59, 69
Classification, difficulty of, 14
Ecological effects, 60, 61
Lakes, use in, 119, 120
Name, chemical, 3, 14, 187
Persistence in soil, 58
Ponds, use in, 119, 120
Reservoirs, use in, 119, 120
Residues, 5, 128
Sites, types of, restriction of, 118
Structure, 179
Toxicity, acute, 52
Toxicity, subacute, 52
Toxicity to animals, 52, 132
Year of initial use, 13
Environment, consequences to, by herbicides used to
control aquatic vegetation:
Agriculture, 124
Fisheries management, 125, 126
Navigation, 126, 127
Property values, 126
Recreation, 125
Water, potable, sources, 126
Wildlife management, 126
Environment, effects on, by herbicides:
Bioaccumulation of residues, 56
Disappearance rate of herbicide residues, 59
Findings, 45, 46
Movement of herbicides in environment, 48, 49
Residues in air, 5, 38, 59, 60
Residues in soil, 4, 37
Residues in water, 5, 59
Residues, methods of detection of, 37, 38
Sources of herbicide contamination in the en-
vironment, 48, 49
Excretion, 35
Fallowing, dry, 153
Fenae, 120, 127, 128, 162,168
191
-------
Fenuron, 13, 23, 61, 164, 187
Fertilization, 105, 106, 110
Fescues, 102, 169, 174
Findings about herbicides and use:
Agricultural use, 75, 76
Analysis, chemical, 11
Aquatic use, 75, 76
Chemistry of herbicides, 11
Environment, effects on, by herbicides, 45, 46
Forestry, use of herbicides with, 77
Grazing lands, 75
Industrial use, 77, 78
Fish as biological control agents, 122, 123
Fish, herbicide residues in, 119
Fisheries management, 114, 115
Flame-ionization detector, 39
Floating plants, 112, 113
Floating weeds, 116
Fluid transmission lines, 158
Foliage spray for brush control, 97, 98
Forage production—weed control methods compared,
107
Forests, weed problem and weed control in:
Brush killers, 88
Chemical control of brush and weeds in forests,
81,82
Dynamic system, forests as, 78
Environmental impact of forest management
practices, 86
Exploitation of forests, history, 79
Findings, 75
Fire as a control, 82, 83
Foliage control, 88
Injection, 89, 90
Mechanical control of brush and weeds in
forests, 82
Operating premises, 79, 80
Rehabilitation of forests, 80, 81
Resource, forests as a, 77
Resource management, 84, 85
Soil-active compounds, 87, 88
Types of herbicides used in forestry, 85, 87
Unique features of forests, 78
Vegetation not controlled in forests, 83
Vegetation removal, chemical and mechanical
means compared, 84
Foxtail, 102
Fruit crop weed control, 9, 151-153
Fruit crops, 9, 151-153
Fruit crops, need for herbicides with, 153
Fumigants, 172
Fungicides, 2, 142
Gas transmission lines, 158
Goldenrod, 110
Grain crops, 153-155
Grass carp, 122
Grasses, cultural weed control of, 171
Grasses in aquatic areas, 121
Grasslike species of weeds in aquatic areas, 121
Grazing lands:
Brush control, advantages, 94
Brush control, biological, 101
Brush control, herbicidal, 97-99
Brush control, mechanical and manual, 99-101
Brush control, methods, 97-110
Brush control, need for, 93
Brush control, problems, 94, 95
Findings, 75
Fire, role, in natural weed control, 95
Herbaceous weeds, 101-104
Management practices accompanying weed con-
trol, 95-97
Native plants become weeds, 95
Pastures, 104-110
Problem of weeds and brush, nature of, 94, 95
Weed control, need for, 93
Weed control, problems, 94, 95
Greasewood, 103
H
Habitat management for row crops, 143
Harding grass, 108
Hazards of herbicides in area of use:
Aquatic areas, hazards to agriculture, 124, 125
Aquatic areas, hazards to recreation, 125
Aquatic areas, hazards to wildlife, 126, 132
Aquatic areas, toxicity hazards to crops, 132
Fisheries management, 125, 126, 131
Forestry, 91, 92
Hazards of use of herbicides, types of:
Drift damage, 91, 92
Livestock contamination, 91
Persistence of herbicides in soil, 58
Precautions for personal,safety, 92
Precautions to minimize drift damage, 92
Stream contamination, 91
Herbaceous weeds, 101-104, 166, 168
Hoary cress, 103
Humus, 58
Hydrolysis:
Acid hydrolysis of carbamates, 23
Acid hydrolysis of thiocarbamates, 25
Base hydrolysis of carbamates, 24
Hydrothal (acrolein). See Acrolein.
I
Impact of forest management practices, 86
Industrial weed control:
Advantages and disadvantages of the different
weed-control methods, 68, 76, 77, 158-168
Animal life affected, 68
Canal banks, 167
Chemical control of weeds, 159-164, 167
Ditch banks, 167
Economics of industrial weed control, 68, 69,
160, 163-167
Effectiveness of nonchemical weed control
methods, 68, 76, 77, 158, 165-168
Mechanical control of weeds, types of methods
of, 158, 159, 166, 167
Pollution resulting from industrial weed con-
trol, 68
Runoff resulting from industrial weed control,
69
192
-------
Inorganic herbicides, 11, 145
Insecticides, 2, 59, 142
Insects as biological control agents of aquatic vegeta-
tion, 123
Instruments for analysis of herbicides. See Residue
detection, methods and techniques.
Irrigation agriculture, 113, 131, 133
Irrigation water, herbicide residues in, 129
Jimsonweed, 104
Karmex (diuron). See Diuron.
Kentucky bluegrass, 169, 174, 175
Larkspurs, 103, 104
Lasso (alachlor). See Alachlor.
Leaching, 49, 55, 57, 58, 183
Leafy spurge, 103
Lespedeza, 106
Lethal concentrations (LCs Q ) in animals. See Toxic-
ity of herbicides and their residues to animals.
Lethal doses (LDs Q ) in animals. See Toxicity of
herbicides and their residues to animals.
Linuron:
Impact on life systems, 6
Industrial use, 162
Lethal doses in animals, 52
Life systems, impact on, 6
Name, chemical, 3, 14, 187
Nutritional content of crops altered with use, 6,
61
Persistence in soil, 58
Properties, 23, 180
Residue in soil, 5, 57
Solid-seeded annual crops, use with, 154, 155
Structure, 180
Toxicity, acute, 52
Toxicity to animals, 52
Year of initial use, 14
Lippia, 169
Liquid chromatography, 43
Lorox (linuron). See Linuron.
Loss of herbicides from target systems—flow chart,
55
Lupines, 103
Livestock contributing to range weed problems,
95,96
Need, 95
Results of brush control, 96, 97
Selection of kind of animal to graze, 96
Timing of livestock grazing, on a range, 96
Manual methods of brush removal:
Burning, 100, 101
Cutting, 99
Grubbing, 99
Marginal plants, 113, 121
Mechanical methods of brush removal:
Bulldozing, 99, 100
Burning, 100, 101
Cabling, 99
Chaining, 99
Disking, 100
Rootplowing, 100, 108
Mechanical weed control in industrial and urban sites:
Blading, 166
Bulldozing, 159, 166
Burning, 159, 166, 167
Bush-hogging, 159
Hand cutting, 158, 166
Planting, 158
Scraping, 166
Seeding, 158
Mechanical weed control in turf, 171, 172
Medusahead, 101, 102
Metabolism, 34, 35, 56
Metabolites, 2, 14, 17, 18, 35
Methods of weed control:
Crops, methods with, 147, 148
Flaming, 151
Fruit, methods with, 151
Grazing, 151
Grazing areas, methods with, 105-110
Mowing, 151
Nut crops, methods with, 151
Solid-seeded annual crops, methods with, 153-
155
Solid-seeded perennial crops, methods with,
156-158
Tillage, 151
Microcoulometry, 39
Milkvetch, timber, 104
Milogard (propazine). See Propazine.
Minor acreage crops, 138, 139
Minor acreage crops, need for herbicides with, 138
Monoculture, 140
Monuron, 118, 162, 164, 187
Mowing, 9, 105, 151
Mule-ears, 103, 108
M
Major acreage crops, 138
Management practices for brush control in grazing
lands:
Animals contributing to range weed problems,
95,96
Arid and semiarid rangelands, 96
Deferred grazing, 96
Forage production improvement as result of
brush control, 96
N
Need for herbicides:
Fruit crops, need with, 153
Minor crops, need with, 138
Nut crops, need with, 153
Row crops, need with, 140, 141
Solid-seeded annual crops, need with, 155
Solid-seeded perennial crops, need with, 156
New herbicides since 1950, 13, 14
193
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Nitralin:
Close chemical relationship with trifluralin, 4
Name, chemical, 3, 14, 187
Structure, 181
Toxicity, acute, 53
Toxicity to animals, 53
Year of initial use, 14
Nonpolar solvent extractions, 37, 38
Nut crop weed control, 151-153
Nut crops, 9, 151-153
Nut crops, need for herbicides with, 153
O
Oak-hickory vegetation, 108
Oats, 6
Orchards, 9, 151-153
Organic herbicides, 12, 138, 145, 146
Paraquat, 31, 32, 102, 103, 108, 128, 157, 162, 176,
187
Paraquat treatment on grazing land, results of, 108
Partridge population, effect of herbicides on, 62, 63
Pasture management, 104, 105, 109
Pasture management systems, estimated costs, 109
Patent protection for herbicides, 139
Pathogens as biological control agents, 123
Persistence of herbicides in crops, 147
Persistence of herbicides in soil, 58
Pest increase because of herbicide use, 6, 61, 62, 66
Pesticide residue monitoring, 5
Pesticides, 1, 2, 4, 35, 57
Phenols, 3, 28-30
Phenoxy herbicides, 105, 106, 110, 154
Phenoxyalkanoic acids, chlorinated, 3, 28-30
Phenylureas, 3, 22, 23, 49
Phreatophytes, 167
Physical methods of row-crop weed control:
Flooding, 143, 144
Heat, 143, 144
Mowing, 143, 144
Smothering, 143
Tillage, 143, 144
Picloram, 3-5, 14, 15, 39, 49, 56, 88-90, 97, 104,
105, 110, 162, 163, 164
Planavin (nitralin). See Nitralin.
Poisonous weeds, 103, 104
Polarography, 40
Postemergence treatment, 157, 184
Preventive weed control with row crops, 142
Propachlor, 3, 14, 16, 27, 53, 58, 181, 187
Propanil, 17, 27, 48, 56, 154
Propazine:
Classification, chemical, 15
Close chemical relationship with atrazine, 2
Name, chemical, 3, 13, 187
Persistence in soil, 58
Properties, 21, 181
Structure, 181
Toxicity, acute, 53
Toxicity to animals, 53
Year of initial use, 13
Pyrolytic gas-liquid chromatography, 41
R
.Revalues, 41
Ragweed, 105, 106, 159
Railroads, weed control at:
Ballast, weed control for, 165
Berms, weed control for, 165
Bridges, weed control for, 165
Chemical control of weeds, 166
Communication lines, weed control for, 165
Ditches, weed control for, 165
Mechanical control of weeds, 165
Rights-of-way, adjacent, weed control for, 165
Shoulders, weed control for, 165
Structures, weed control for, 165
Switches, weed control for, 164
Yards, weed control for, 164
Ramrod (propachlor). See Propachlor.
Red clover, 6
Residue detection, methods and techniques:
Adsorption, chromatography, 38
Affinity detector, use of, 39
Atomic absorption, 40
Chromatogram, gas, use of, 40
Chromatography, gas-liquid, 38
Chromatography, pyrolytic gas-liquid, 41
Cleanup, 37
Colorimetry, 39, 40
Confirmation of herbicide residue detection,
40-42
Derivatization, 41
Determination, part of residue analysis, 37
Electrolytic conductivity detector, use of, 39
Electron-capture detector, 39
Extraction, 37, 38
Flame-ionization detector, use of, 39
Halogen detectors, 40
Mass spectrometry, 39, 40
Microcoulometry, 39
P-values, 41
Polarography, 40
Rt values, 41
Soxhlet extraction, 37
Specificity of residue detection, 40
Spectrophotometers, 39
Thin-layer chromatography, 38, 41, 42
Two-dimensional thin-layer chromatography,
41
Types of detectors listed and compared, 38
Residues. See also Residue detection, methods and
techniques.
Air, residues in, 59, 60
Analysis, chemical, of herbicides from residues,
36-43
Bioaccumulation of, residues, 56, 57
Crops, residues in, 130, 131
Dissipation in ponded water, 128
Irrigation water, residues in, 131
Livestock, residues in, 130, 131
Outlook, current, 42, 43
Ponds, residues in, 128
Soil, residues in, 57, 58
Studies, residue, 128-131
194
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Water, residues in, 59, 127-131
Results of brush control, 97
Re-treatments for annual and perennial weed control,
106
Rights-of-way for utilities, weed control on, 158-164
Rootplowing, 100, 108
Rotation of herbicides, 148, 149
Row crops:
Biological weed control, 142
Chemical weed control, 144-148
Competition of plants, 141, 142
Habitat management, 143
Herbicides for row crops, 145-150
Losses, 140, 141
Methods of weed control, 142-145, 147-150
Need for weed control, 140
Nonchemical weed control, 142-144
Persistence of herbicides in row crops, 147
Physical methods of weed control, 143, 144
Practices of weed control, 140, 147-150
Principles of weed control, 140, 147-150
Systems of weed control for row crops, 147,
148
Sagebrush, 100, 110
St. Augustine grass, 169, 176
Scarification, 78
Siduron, 102, 176, 187
Silvex, 4, 5, 13, 15, 19, 88, 98, 105, 117, 120, 121,
127, 128, 129, 162, 176, 182, 187
Simazine, 13, 15, 21, 61, 62, 87, 88, 157, 162, 176,
187
Snails, 123
Sneeze weeds, 104
Social impact of restricting use of aquatic herbicides,
133, 134
Sodium arsenite, 11, 162
Soil applications of herbicides for brush control, 98
Soil/root treatments, 164
Solid-seeded annual crops:
Alternatives to herbicides, 155
Drift of herbicides, 154, 155
Herbicides, 153-155
Methods of weed control, 153
Need for herbicides, 155
Practice of weed control, 153
Principles of weed control, 153
Solid-seeded perennial plants:
Competition between crop and weeds, 155-157
Herbicides, 155-157
Importance of weed control, 155, 157
Postemergence treatments, 157
Problem of weeds with solid-seeded perennial
crops, 155, 156
Timing of planting—influence on weed species
that grow in crops, 156
Soxhlet extraction, 37
Spectrophotometers, 39
Spray-drift problem with herbicides used with grain
crops, 154, 155
Spraying, basal, 163, 164
s-Triazines, 3, 15, 21
Structure, chemical, of herbicides, 179, 180
Stump spraying, 163, 164
Subclover, 108
Submersed plants:
Application rates for herbicides, 127
Canals, 117, 118
Characteristics, 113
Difficulty of controlling submersed plants, 117
Ditches, 117-119
Drainage ditches, 118, 119
Herbicides for submersed plants, 117, 118
Residues of herbicides, 127-129
Sunlight, 60
Sutan (butylate). See Butylate.
Synthesis of herbicides, 18
Systemic herbicides, 4, 57
TCAB (3,3',4,4'-tetrachloroazobenzene), 17
TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), 17
Tarbrush, 100
Target systems, loss from, 55
Tetrachloroazobenzene—3,3 ,4,4 -tetrachloroazoben-
zene (TCAB), 17
Tetrachlorodibenzo-p-dioxin—2,3,7,8-tetrachlorodi-
benzo-p-dioxin (TCDD), 17
Thin-layer chromatography, 38, 41, 42
Thiocarbamate herbicides, 25
Timber milkvetch, 104
Toxicity, acute, 50-54, 132
Toxicity of herbicides and their residues to animals:
Animals (nonhuman), toxicity to, 50-54, 131,
132
Lethal concentrations (LCso) in animals, 50-54
Lethal doses (LD5 0) for animals, 50-54
Toxicity of herbicides and their residues to crops, 10,
91, 92, 103, 124, 125, 130, 132
Toxicity of poisonous plants to livestock, 103, 104
Toxicity, oral, 50-54
Toxicology of herbicides and their residues. See
Toxicity of herbicides and their residues to ani-
mals.
Training requirements for users of aquatic herbicides,
134
Treatment of individual trees by herbicides, 90
Treflan (trifluralin) See Trifluralin.
Triazines, 3, 12, 15, 21, 22, 146, 154, 157
Trichlorophenoxyacetic acid—2,4,5-Trichlorophe-
noxyacetic acid (2,4,5-T):
Air, particles from, containing 2,4,5,-T, 60
Amount of use, 66
Classification, chemical, 2, 3, 15
Dominance on market, 18
Economic aspects of use, 68
Environment, effect on, 49
Exports, 20
Forestry, use in, 88-91
Grazing lands, use with, 97, 98, 105, 108, 110
Impurities, 17, 19, 33, 34, 49
Industrial use, 68, 159, 162, 163, 168
Lack of supply, 20
Leaching, 58
Name, chemical, 188
Pastures, use with, 105, 108, 110
Production, 19, 20
195
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Properties, 19
Residues in soil, 57
Residues in water, 5, 59
Urban use, 159, 160
Trifluralin:
Amount of use, 65
Close chemical relationship to nitralin, 2, 4
Ecological effects, 53, 54, 60, 62
Grass weeds, control of, 146, 149
Increase in broadleaf weeds from control of
grass weeds, 149
Leaching, 57
Name, chemical, 3, 14, 188
Persistence, necessity of, 147
Persistence of residues in soil, 5, 57, 58
Properties, 31, 181
Relationship, chemical, to nitralin, 4
Residues, persistence of, in soil, 5, 57, 58
Row crops, use with, 146
Structure, 31, 181
Tadpoles, lethal concentration in, 60
Toxicity, acute, 53, 54, 60
Toxicity to animals, 53, 54, 60, 62
Year of initial use, 14
Turfs:
Chemical weed control, 172-177
Classification of plants into turfgrass or weeds—
variation with locality or use, 170
Cultural weed control, 171
Decomposition of herbicides in turfs, 172-177
Expenditures for turf maintenance, 170
Herbicides, 173-177
Maintenance, expenditures for, 170
Mechanical control of weeds, 171, 173-177
Problem of weeds, 170, 171
Use of turfs, 168, 169
2,4-D. See Dichlorophenoxyacetic acid—2,4-
Dichlorophenoxyacetic acid (2,4-D).
2,4-Dichlorophenoxyacetic acid. See Dichlorophe-
noxyacetic acid—2,4-Dichlorophenoxyacetic acid
(2,4-D).
2,4,5-T. See Trichlorophenoxyacetic acid—2,4,5-
Trichlorophenoxyacetic acid (2,4,5-T).
Types of herbicides:
Aquatic areas, herbicides used in, 115-122,
127-129
Domestic areas, herbicides used in, 172-177
Forests, herbicides used with, 84-90
Fruit crops, herbicides used with, 152
Grazing lands, herbicides used with, 97, 98,
102-110
Industrial sites, herbicides used with, 159-164,
168
New herbicides since 1950, 13, 14
Nut crops, herbicides used with, 152
Pastures, herbicides used with, 105-110
Recreational areas, herbicides used in, 172-177
Row crops, herbicides used with, 145-147
Solid-seeded annual crops, herbicides used with,
154,155
Solid-seeded perennial crops, herbicides used
with, 156, 157
U
Uracil derivatives, 3, 16, 33, 88
Uracil derivatives, properties of, 33
Urban sites, 158-177
Ureas, 12
Utility rights-of-way, weed control on, 158-164
Vascular aquatic plants, 112, 113, 115, 118, 119
Volatility of herbicides, 6, 49, 66
W
Water, potable, herbicides and their residues in, 129
Waterferns, 116
Waterhyacinth, 112, 114-117
Waterlettuce, 116, 117
Weed control methods alternative to herbicide use:
Aquatic areas, 69, 70, 121, 122
Crops, 64, 148, 149, 153, 155
Forests, 82-84
Grazing lands, 96, 97, 99-101, 106
Industrial areas, 68, 69, 76, 77, 158, 159
Weeds, aquatic. See Aquatic vegetation.
Weeds, aquatic, under chemical control:
Algae, 115, 116
Emersed and marginal weeds, 120, 121
Floating weeds, 116, 117
Lakes, ponds, reservoirs, aquatic weeds in, 119,
120
Submersed weeds in drainage ditches, 118, 119
Submersed weeds in irrigation canals and
ditches, 117, 118
White clover, 106
Whorled milkweed, 103
Wildlife, herbicide residues in, 130
Wildlife management, 114, 126
X, Y, Z
Xylene, 3, 5, 54, 59, 117, 118, 130, 132, 181
Xylene dispersion in flowing water, features of, 130
Year of initial use of new herbicides, 14, 15
Zoysias, 169, 175, 176
196
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO,
EPA-SAB-74-001
3. RECIPIENT'S ACCESSION NO.
4 TITLE AND SUBTITLE
Herbicide Report; Chemistry and Analysis, Environmental Effects,
Agricultural and Other Applied Uses
5. REPORT DATE
May 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Hazardous Materials Advisory Committee and Consultants
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Hazardous Materials Advisory Committee
Science Advisory Board
U.S. Environmental Protection Agency
Washington, B.C. 20460
10. PROGRAM ELEMENT NO.
1HA410
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Washington, B.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA/100/00
15, SUPPLEMENTARY NOTES
16. ABSTRACT
Selected herbicides are discussed under the headings of chemistry and analysis, environmental effects, and agri-
cultural and other applied uses.
The groupings employed are based on chemical structure and recognize 13 major groups of herbicides: chlorinated
phenoxyalkanoic acids, s-triazines, phenylureas, carbamates, thiocarbamates, amides, chlorinated aliphatic acids, chlorinated
benzole acids, phenols, substituted dinitroanilines, bipyridiniums, arsenicals, uracils, and miscellaneous. Synthesis, analysis,
and properties are discussed for each of these groups, and consideration is given to specific analytical methods and to general,
multiresidue methods such as gas-liquid chromatography.
Environmental effects of herbicides are described in terms of sources and movements of herbicides; residues in soil,
water, and air; bioaccumulation of residues; effects on nontarget plants; and the costs and benefits of herbicide use.
The principal uses of herbicides are on croplands, grazing lands, forests, orchards, aquatic habitats, and industrial
sites and other noncrop lands. Each of these topics is covered in detail, and herbicide use is compared with alternative
methods with regard to efficacy and economics.
The principal uses of herbicides are on croplands, grazing lands, forests, orchards, aquatic habitat, and industrial site
and other noncrop lands. Each of these topics is covered in detail, and herbicide use is compared with alternative methods
with regard to efficacy and economics.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Agricultural chemicals
Aquatic weed control
Biological control
Brush control
Chemcontrol
Farm management
Fisheries management
Forest management
Herbicides
Land management
Pesticides
Weed control
Organic pesticides
Pesticide drift
Pesticide residues
Pesticide toxicity
06F
07C
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS {ThisReport)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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