PROTECTING GROUND WATER:
PESTICIDES AND AGRICULTURAL PRACTICES
U.S. Environmental Protection Agency
Office of Water
Office of Ground-Water Protection
401 M Street, S.w.
Washington, D.C.
«'.S. Environmental :
joglon 5, Library (:
230 S. Dearborn Stre-- -
OMcago, IL 60604
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FOREWORD
State and local governments throughout the country are
seeking to address the problem of pesticide contamination as
part of their ground-water protection programs. Encouraging
the sound choice and management of pesticides is generally
recognized as an important element of these programs, but very
little information has been readily available to aid in
selecting management practices to help reduce the risk of
pesticide contamination. As part of a continuing effort to
provide information to officials in State and local government
involved in ground-water protection, the Office of Ground-Water
Protection of the U.S. Environmental Protection Agency
initiated a project to identify and evaluate the potential
impacts on ground water of various agronomic, irrigation, and
pesticide application practices. The results of the study are
presented in this report, "Protecting Ground-Water: Pesticides
and Agricultural Practices."
Since site conditions, crop and pest patterns, and agri-
cultural practices vary widely, no single set of
recommendations can be developed that would be appropriate for
all situations. The purpose of this report is to explain the
principles involved in reducing the risk of pesticide
contamination and describe what is known about the impact of
various agricultural practices on pesticide leaching. With
this basic understanding, it is hoped that water qjuality
officials can work with their colleagues in the agricultural
community to design and implement protection programs suited to
specific conditions in their areas.
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PREFACE
This report, "Protecting Ground-Water: Pesticides and
Agricultural Practices," was prepared by the Office of
Ground-Water Protection (OGWP), U.S. Environmental Protection
Agency. Donna Fletcher, Senior Analyst, OGWP, served as the
Task Manager and Project Officer. Ron Hoffer, Director,
Guidelines Implementation Staff, OGWP, provided additional
guidance. The project was conducted as part of a continuing
effort led by Marian Mlay, Director of OGWP, and Susan Wayland,
Deputy Director of the Office of Pesticide Programs, to address
the problem of pesticides in ground water.
An EPA technical committee comprised of Dr. Robert Hoist of
the Office of Pesticide Programs, Robert Carsel of the Office
of Research and Development, Carl Myers of the Office of Water
Regulations and Standards, and Ken Adler of the Office of
Policy Analysis provided technical support arid participated in
the review of preliminary drafts. Drafts were also reviewed
and discussed by a panel of experts from Federal and State
water quality and agricultural agencies and the industrial,
academic, and environmental communities who are listed on the
next page.
The report was developed with technical support from
Dames & Moore under EPA Contract No. 68-03-3304. The principal
contributors to the report from Dames & Moore were
Surya S. Prasad, Ph.D., CPSS, CPAg, Senior Soil Scientist and
Project Manager, and Robert Kalinski, Hydrogeologist.
11
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ACKNOWLEDGMENTS
The U.S. Environmental Protection Agency expresses its
appreciation to the following individuals who participated in
the review of preliminary draft reports and a workshop held May
20-22, 1987, in Bethesda, Maryland.
Panelists
Timothy Amsden, Office of Ground Water, U.S. Environmental
Protection Agency, Region VII
Dr. James Baker, Department of Agricultural Engineering, Iowa
State University
Fred Banach, Connecticut Department of Environmental Protection
John E. Blodgett, Environmental and Natural Resources Policy
Division, Congressional Research Service
Katherine Brunetti, California Department of Food and
Agriculture
Dr. Rodney DeHan, Florida Department of Environmental
Regulations
Orlo (Bob) Ehart, Wisconsin Department of Agriculture, Trade and
Consumer Protection
Thomas J. Gilding, National Agricultural Chemicals Association
Dennis Grams, Nebraska Department of Environmental Control
Dr. George Hallberg, Iowa Department of Natural Resources
Dr. Charles Helling, Pesticide Degredation Laboratory,
Agricultural Research Service, U.S. Department of
Agriculture
Dr. Maureen Hinkle, National Audubon Society
Dr. Patrick Holden, Water Science and Technology Board,
National Academy of Sciences
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Russell Jones, Rhone-Poulenc Agricultural Company
Lou Kirkaldie, Soil Conservation Service, U.S. Department of
Agriculture
Raymond Knox, South Carolina Department of Health and
Environmental Control
Dr. Terry Logan, Department of Agronomy, The Ohio State
University
James Lake, Conservation Technology Information Center,
National Association of Conservation Districts
Dr. William McTernan, School of Civil Engineering, Oklahoma
State University
Dr. Richard Maas, Water Quality Group, North Carolina State
University
Dr. James Schepers, Department of Agronomy, University of
Nebraska and Agricultural Research Service,
U.S. Department of Agriculture
Dr. David Schertz, Soil Conservation Service, U.S. Department of
Agriculture
Velma Smith, Environmental Policy Institute
Dr. Fred Swader, Extension Service, U.S. Department of
Agriculture
Dr. Heather Wicke, Environmental Law Institute
IV
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DISCLAIMER
The mention of trade names of commercial products and
instruments in this report is for illustration and does not
constitute preferential treatment or endorsement or
recommendation for use.
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TABLE OF CONTENTS
Page
Number
PART I: OVERVIEW AND OBJECTIVES OF MEASURES
TO REDUCE PESTICIDE CONTAMINATION OF
GROUND WATER 1
CHAPTER ONE: INTRODUCTION 2
Pesticides and Ground-Water Protection
Programs 2
Background of the Project 4
Scope of the Project 4
Organization of Report 5
CHAPTER TWO: OVERVIEW OF FACTORS CONTROLLING PESTICIDE
LEACHING 6
Pesticide Properties Conducive to Leaching. . 6
Soil Conditions Conducive to Leaching .... 8
Other Factors 13
CHAPTER THREE: OBJECTIVES OF MITIGATION MEASURES TO
REDUCE PESTICIDE CONTAMINATION
OF GROUND WATER 14
Minimizing Pesticide Usage 15
Using Pesticides with Lower Leaching
Potential 15
Reducing Pesticide Application at Times
Most Likely to Promote Leaching 15
Preventing Accidents, Spills, and Pathways
for Pesticides to Reach Ground Water. ... 16
Selecting Combinations of Practices 17
PART II: POTENTIAL IMPACT OF AGRICULTURAL
PRACTICES ON PESTICIDE CONTAMINATION
OF GROUND WATER 19
CHAPTER FOUR: PESTICIDE APPLICATION
FACTORS 20
Fixed Practices 20
Application Methods 20
VI
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TABLE OF CONTENTS
(Continued)
Page
Number
Variable Practices 22
Choice of Pest Control Method 22
Application Timing 23
Application Rate and Volume 27
CHAPTER FIVE: FARMING PRACTICES 29
Fixed Practices 29
Tillage Practices 29
Contour Farming 32
Terracing 32
Contour Stripcropping 32
Cover Crops 33
Variable Practices 33
Crop Rotation . . 33
Planting Pest-Resistant Varieties 35
Adjusting Planting and Harvesting Times. ... 35
Integrated Pest Management 35
CHAPTER SIX: IRRIGATION PRACTICES 38
Fixed Practices 38
Methods of Irrigation 38
Variable Practices 41
Irrigation Timing 41
Irrigation Volume and Frequency 42
CHAPTER SEVEN: OTHER PRACTICES TO REDUCE CONTAMINATION
POTENTIAL 43
Handling and Disposal of Pesticides and
Pesticides Products 43
Chemical Anti-Backsiphoning Devices 46
Buffer Zone Establishment 48
Proper Well Sealing and Abandonment 49
Avoiding Sinkholes in Areas of Karst or
Subsidence 50
Sealing of Agricultural Drainage Wells .... 52
Subsurface Drainage and Treatment 52
Farm Ponds and Irrigation Reuse Pits 53
VII
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TABLE OF CONTENTS
(Continued)
Page
Number
TABLES
TABLE 2-1 PHYSICAL AND CHEMICAL CHARACTERISTICS OF
PESTICIDES INFLUENCING LEACHING
POTENTIAL 9
TABLE 2-2 PESTICIDES AND RELATED CHEMICALS INCLUDED
IN EPA'S NATIONAL SURVEY OF PESTICIDES IN
WELL WATER 10
TABLE 5-1 POSSIBLE EFFECTS OF FARMING FACTORS ON
QUANTITIES OF PESTICIDES USED 34
TABLE 6-1 POTENTIAL FOR PESTICIDE LEACHING WITH
VARIOUS METHODS OF IRRIGATION AND
PESTICIDE APPLICATION 39
TABLE B-l DEGRADATION RATE CONSTANTS FOR SELECTED
PESTICIDES ON FOLIAGE B-2
TABLE B-2 SOIL DEGRADATION RATE CONSTANTS FOR
SELECTED PESTICIDES B-4
TABLE D-2 SOURCES OF INFORMATION D-5
FIGURES
FIGURE 4-1 PESTICIDE APPLICATION RELATIVE TO
CROP GROWTH STAGE, WEED AND PEST
OCCURRENCE 25
FIGURE 7-1 CHEMIGATION SYSTEM WITH ANTI-BACKSIPHONING
DEVICE 47
FIGURE 7-2 KARSTIC GROUND-WATER CONDITIONS 51
FIGURE C-l PATTERNS OF SOIL ORDERS AND SUBORDERS
OF THE U.S C-2
Vlll
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TABLE OF CONTENTS
(Continued)
Page
Number
APPENDICES
APPENDIX A REFERENCES CITED A-l
APPENDIX B DEGRADATION RATE CONSTANTS FOR
SELECTED PESTICIDES B-l
APPENDIX C DOMINANT SOIL ORDERS OF THE U.S C-l
APPENDIX D INFORMATION SOURCES D-l
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PART I
OVERVIEW AND OBJECTIVES OF
MEASURES TO REDUCE PESTICIDE CONTAMINATION
OF GROUND WATER
Part I describes the context for ground-water
protection efforts addressing pesticides, the factors
influencing the leaching of pesticides, and the objectives of
measures to reduce pesticide contamination of ground water
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CHAPTER ONE
INTRODUCTION
Pesticides and Ground-Water Protection Programs
Increased awareness of the need to protect the nation's
vital ground-water resources has led to the development of
programs at the Federal, State, and local levels to control
potential sources of contamination. One of the principal goals
of the U.S. Environmental Protection Agency's (EPA)
Ground-Water Protection Strategy, issued in 1984, was to
control sources of contamination of particular national
concern. In the Strategy, pesticides were named as a source
needing additional national attention. Since that time, the
Agency has increased efforts to review the potential
ground-water impacts of pesticides and take regulatory action
on specific chemicals found to pose a risk to ground water.
The Agency has also initiated a National Survey of Pesticides
in Well Water to better characterize the problem. In addition,
the Agency conducted an extensive review of the magnitude,
sources, and potential health impacts of pesticides in ground
water and the statutory and program authorities available to
help address the problem. This work led the Agency to select
the topic of agricultural chemicals in ground water for a major
strategic initiative that is still underway.
During this same period, many States also began efforts to
understand and address pesticide contamination of ground
water. These efforts have been stimulated, in part, by the
development of State ground-water protection strategies. EPA
has supported State strategy development through grants under
Section 106 of the Clean Water Act as a means for strengthening
the capacity of State governments to protect ground-water
quality, another principal goal of EPA's Ground-Water
Protection Strategy. Nearly all of the State strategies
recognize the need to address pesticides as part of the
ground-water protection program. However, because the
pesticide contamination problem is a relatively recent
discovery and involves complex technical and institutional
questions, programs to address pesticides in ground water are
less developed than for other sources of contamination.
The enactment of amendments to the Safe Drinking Water Act
(SDWA) in 1986 provided EPA with a statutory basis for
promoting comprehensive protection of the nation's ground water
as a vital resource. Under the new Wellhead Protection
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Proaram, States will be delineating areas around public water
supply wells and instituting management programs to protect
these wells from all sources of potential contamination EPA
may provide financial and technical support. Another SDWA
amendment establishes a demonstration program for protecting
cri?icil aquifer protection areas in designated Sole Source
Aquifers. Since pesticides are a potential source of
contamination for public water supply wells a*d Critical
aquifer protection areas, EPA anticipates that many State and
local governments will seek to develop programs that address
this source.
The recent reauthorization of the Clean Water Act provides
additional impetus for addressing pesticide contamination as a
nonpoint source for both surface and ground water. Under the
new Nonpoint Source Management Program, States can be eligible
?o receive funding for ground-water protection activities. EPA
expects that many States will seek to control pesticide
examination as part of their comprehensive nonpoint programs-
Under the Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA), EPA has regulatory responsibility for determining
whether a pesticide can be or remain registered and also for
specifying by label, how the pesticide can be used. This
aSritygis being used to evaluate the leaching potential of
individual chemicals. Regulatory actions such as label
changes, restricted use classification, and cancellation will
continue to be made when needed to protect ground water. These
actions on a chemical-by-chemical basis will define the
chemicals posing a risk to ground water and establish
requirements for using these chemicals.
While regulatory actions on specific chemicals are a
fundamental element of efforts to control pesticide
c^Safion State and local governments will also be seeking
to address pesticides in the broader context of their
around-water protection programs and in a way that is suited to
?hHgr!cu!tu?a? conditions in their areas. These programs
will be looking beyond the pesticide regulatory Process for
ways to manage pesticide use to minimize risks to ground water
resources.
The Aaencv recognizes that technical information on
practices^ Ld^hese risks is needed to help in the design
and implementation of programs addressing pesticide
cont^inatfon at the State and local levels. To help meet this
need EPA's Office of Ground-Water Protection undertook a study
?o evaluate the potential ground-water impacts of various
agronomic and pesticide application practices. Since there has
Sen °nly limited research in this area, the Agency also drew
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together experts in the field to gain their insights into what
steps can be taken to reduce risks of pesticide contamination.
This report presents the findings of the study and expert panel
discussions.
Background of the Project
As mentioned earlier, the Agency is now developing a
strategy for agricultural chemicals in ground water as an out-
growth of preliminary investigations to understand the scope of
the problem and identify policy issues. Findings of the
initial working group on pesticides in ground water, co-led by
the Office of Pesticide Programs and Office of Ground-Water
Protection, were published in a 1986 report entitled
"Pesticides in Ground Water: Background Document." Readers
seeking a detailed discussion of the extent and causes of
pesticide contamination, its potential environmental and human
health impacts, and the statutory authorities and programs
available to address it should obtain a copy from the Office of
Ground-Water Protection, U.S. Environmental Protection Agency,
WH-550-G, Washington, D.C. 20460.
In exploring potential solutions, it soon became apparent
that little information was readily available to aid in
selecting management practices that would help reduce the risk
of contaminating ground water from pesticide use. Recognizing
that encouraging sound choice and management of pesticides
would be an important element of ground-water protection
programs at all levels of government, the Office of
Ground-Water Protection initiated a project to identify and
evaluate the potential impact of various agronomic and
pesticide application practices on ground water.
This report presents the results of an extensive literature
review and interviews with experts in several disciplines. The
draft report was reviewed by a panel of experts from the
research community, Federal and State agriculture and water
quality agencies, and industry and environmental organizations
who participated in a three day workshop to discuss the
findings to assure that they represent the best professional
judgement now available on this topic.
Scope of the Project
The problem of pesticides in ground water is extremely
complex. Pesticides can enter ground water from activities at
any point in their manufacture, commercial distribution,
storage, use on land or in industrial settings, and disposal.
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The leaks, spills/ and other releases that can occur wherever
bulk pesticides are stored, handled, or disposed of can result
in ground-water contamination; several laws and regulations
already address these potential sources.
By far, pesticides are most commonly used to control in-
sect and weed pests on the land. While they are also used on
lawns and gardens, forest lands, and rights of way, the
greatest use of pesticides is on land in crop production.
Under certain conditions, some pesticides applied to the land
can leach to the ground water from normal application. Tne
focus of this report is on reducing leaching from agricultural
use of pesticides; some practices to minimize on-farm releases
and spills are also addressed. It should be noted that many of
the considerations and practices suggested may also apply to
non-agricultural use of pesticides.
It is recognized that long-term solutions to the problem of
pesticides in ground water could involve changes in how and
where crops are grown, implementation of pest control metnods
that are less chemically dependent, and development and use of
new chemicals that present a lower risk to ground water and
human health. This report, however, assumes tnat in the more
immediate term, farmers will continue growing crops in areas
where ground water may be vulnerable to contamination and will
be using chemicals that have some potential to leach. The
purpose of the report is to provide State and local regulatory
officials with technical information pertaining to measures for
reducing pesticide leaching to ground water that can aid in the
design of programs to prevent ground-water contamination from
pesticides.
Organization of Report
Part I of this report contains background information on
the pesticide properties, site conditions, and other factors
influencing the likelihood of pesticide contamination. It also
contains an overview of basic principles for reducing pesticide
contamination that provides a framework for developing and
implementing protection measures.
Part II of the report contains detailed discussions of tne
potential impacts of various farming, pesticide application,
and irrigation practices on pesticide leaching. Tnis
information can be used as a starting point for development and
fostering use of management practices that are appropriate to
the conditions in a particular area.
The appendices contain references, national maps of soils
and climatic conditions, and a list of other sources that can
provide information useful in the development of ground-water
protection programs addressing pesticides.
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CHAPTER TWO
OVERVIEW OF FACTORS CONTROLLING PESTICIDE LEACHING
A complex set of factors influence the likelihood of
pesticide contamination of ground water in a given location:
the physical and chemical properties of the pesticide, natural
hydrogeologic and man-made features at the site of application,
and the agronomic and pesticide application practices
employed. The following summary of pesticide properties and
site conditions most conducive to leaching is provided as
background for the more detailed discussion of practices
influencing leaching potential that are the primary focus of
this report.
Pesticide Properties Conducive to Leaching
Although ground-water contamination by pesticides is a
relatively recent public concern, a significant amount of
research on the environmental fate of pesticides has either
directly or indirectly provided some understanding of the
problem. In particular, a great deal of work addresses the
fate of pesticides in soil. As a result, a better
understanding of the relative leaching potential of various
pesticide classes exists than perhaps any other aspect of the
problem. Recent monitoring of ground water has provided data
that have improved and confirmed understanding of what makes a
pesticide more likely to leach. The following are the
important physical and chemical characteristics of a pesticide
that may make it conducive to leaching, based on current
scientific understanding (EPA, 1986) .
Water solubility: the propensity for a pesticide to
dissolve in water. The higher a non-ionic pesticide's
water solubility, the greater the amount of pesticide
that can be carried in solution to surface water and
ground water. Water solubility of greater than 30 ppm
has been identified as a "flag" for the possibility of
a pesticide to leach.
Soil adsorption: the propensity of a pesticide to
adhere to soil particles, which is defined as the
ratio of the pesticide concentration in soil (Cs) to
the pesticide concentration in water (K^;
CS/-CW). There are different mechanisms for
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pesticide adsorption in soils, with particularly
important differences between clays and soil organic
matter. A second measure, Koc, is used to help ^
characterize the mechanism of adsorption. Koc is a
measure of the pesticide adsorption to the organic
component of the soil. The lower a pesticide s Kd
and Koc values, the less likely these chemicals J^?;
be adsorbed to soil particles and the more likeJY they
will leach to ground water. Of the pesticides found
In ground wate? to date, most have had K£ values of
less than 5, and usually less than 1. These
ground-water contaminants have also generally been
shown to have Koc values of less than 300.
Volatility: the propensity for a pesticide to dis-
^r^FTnto the air. Volatility is primarily a _
function of_the vapor_ pressure^^the^hemical^and is ^
r.
wa?er Solubility can cause pesticides with high vapor
'1
rainfall.
||Mlff^ip-ionm?n1so?l9Sra^ymmeSasu?eras
^-ha?f?he^^rent?^lofot°a^s?l&d£often
referred to as a pesticide's soil half-lite.
of pesticides in soil is dependent on a
nunfceoenvr
several decomposition processes that cause chemical breakdown,
^sforma^
wa?er Photolysis is the breakdown of a chemical from exposure
to the energy of the sun. And, microbial transformations
resul? f^the metabolic activities of microorganisms within
the soil When a pesticide resists these decomposition
processes and does^ot readily evaporate, ^^^'^
Le st? i e Fi""*
era
or three weeks y have a higher potential to leach to
ground water.
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Concern for ground-water contamination by pesticides has
led EPA to focus more attention on identifying those having the
greatest potential to leach through the Agency's pesticide
registration and re-registration process. EPA has begun to
examine every pesticide for chemical and physical properties
that would, as described above, indicate their potential to
leach. Table 2-1 provides a summary of the threshold values
for those key factors indicating that a pesticide has a high
potential to leach. It is important to note, however, that no
single threshold will indicate leachability.
Presently, insufficient data exist to state with certainty
which pesticides have the greatest potential to leach from
normal application to land. In preparing for the National
Survey of Pesticides in Well Water, however, EPA developed a
list of pesticides suspected, of having a potential to leach
based on their properties, use patterns, and available
monitoring data. The pesticides shown in Table 2-2, along with
selected pesticide metabolites or degradation products, are the
pesticides included in the National Survey. Pesticides marked
with an asterisk on the list are those for which monitoring
data shows the pesticide has leached .as a result of normal
use. Other pesticides shown are those that EPA considers,
based on current knowledge, to have the potential to leach to
ground water.
Soil Conditions Conducive to Leaching
The site conditions at the area receiving a pesticide can
greatly affect the likelihood of any leaching. The composition
and properties of the soil are the two most important factors
affecting leaching potential. These factors are discussed
below.
Soil Composition
Clay minerals content: contributes to cation exchange
capacity (CEC), the ability of the soil to adsorb
positively charged ions or molecules (i.e., cations).
Positively charged pesticides may be adsorbed to soil
containing negatively charged clay particles.
Clay soils: defined as soils with a predominance of
particles less than 2 micrograms in size; particle
size is generally proportional to the amount of clay
mineral contained. They have a high surface area
which contributes further to adsorption capacity.
Adsorption onto clay colloids leads to chemical
degradation and inactivation of some pesticides, but
it inhibits degradation of others.
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TABLE 2-1- PHYSICAL AND CHEMICAL CHARACTERISTICS OF PESTICIDES
INFLUENCING LEACHING POTENTIAL
Pesticide Characteristic
Value or Ranged
Water solubility
Koc
Henry's Law Constant
Spec i at ion
Hydrolysis half-life
Photolysis half-life
Field dissipation half-life
Greater than 30 ppm
Less than 5, usually less than 1
Less than 300 - 500
Less than 10~2 atm-m"3 mol
Negatively charged, fully or
partially at ambient pH
Greater than 25 weeks
Greater than l week
Greater than 3 weeks
contamination .
Source: U.S. EPA, 1986
indicating the potential for ground-water
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TABLE 2-2:
PESTICIDES AND RELATED CHEMICALS INCLUDED
IN EPA's NATIONAL SURVEY OF PESTICIDES
IN WELL WATER
Acifluorfen (H)
Alachlor (H)
Aldicarb (I)
Ametryn (H)
Atrazine (H)
Bromacil (H)
Butylate (H)
Carbaryl (I)
Carbofuran (I)
Carbofuran-3-OH
Carboxin (F)
Chloramben (H)
alpha-Chlordane (I)
gamma-Chlordane (I)
Chlorothalonil (F)
Cyanazine (H)
Cycloate (H)
2,4-D (H)
Dalapon (H)
Dibromochloropropane (N)
DCPA (H)
Diazinon (I)
Dicamba (H)
3,5-Dichlorobenzoic acid (H,I)
1,2-Dichloropropane (N)
Dieldrin (I)
PESTICIDES
Dinoseb (H)
Diphenamid (H)
Disulfoton (I)
Diuron (H)
Endrin (I)
Ethylene dibromide (I,N)
Fluometuron (H)
Heptachlor (I)
Hexachlorobenzene(s)
Methomyl (I,N)
Methoxychlor (I)
Metolachlor (H)
Metribuzin (H)
Oxamyl (I)
Pentachlorophenol (H)
Picloram (H)
Propachlor (H)
Propazine (H)
Propham (H)
Propoxur (I)
Simazine (H)
2,4,5-T (H)
2,4,5-TP (H)
Tebuthiuron (H)
Terbacil (H)
Trifluralin (H)
These pesticides and related chemicals are considered by EPA to
have the greatest potential for leaching to ground water.
F - Fungicide
H - Herbicide
I - Insecticide
N - Nematicide
S - Seed Protectant
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TABLE 2-2 (continued)
PESTICIDE METABOLITES
Aldicarb sulfone Fenamiphos sulfoxide
Aldicarb sulfoxide Heptachlor epoxide
Atrazine, dealkylated Hexazinone
Carboxin sulfoxide Methyl paraoxon
DCPA acid metabolites Metribuzin DA
5-Hydroxy dicamba Metribuzin DADK
Disulfoton sulfone Metribuzin DK
ETU Pronamide metabolite, RH 24850
Fenamiphos sulfone
Source: U.S. EPA, 1986
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Organic matter content: contributes to adsorption of
pesticides in soil. Organic matter content affects
biological activity, bioaccumulation, biodegrad-
ability, leachability, and volatility of pesticides.
Soils with high organic content adsorb pesticides and
therefore inhibit their movement into ground water.
Soil Physical Properties
Soil texture: refers to the relative proportion of
different sizes of soil particles (i.e., percent sand,
silt, and clay). Leaching is more rapid and deeper in
coarse or light (sand textured) soils than in fine or
heavy (clay) soils.
Soil structure: refers to the way soil grains are
grouped together into larger aggregates - platy,
prismatic, blocky, or spheroidal (granular and crumb).
Structure is affected by texture and percent of
organic matter. Pesticides and water can seep,
relatively unimpeded, through seams between the
aggregates.
Porosity: is a function of pore size and pore size
distribution determined by soil texture, structure,
and particle shape. Pesticides are more likely to be
transported to a greater degree through more porous
soils, all other things being equal.
Soil moisture: refers to the presence of water in
soil. The soil water ultimately transports pesticides
that are not adsorbed onto soil particles in the
unsaturated bone to the water table below. Upward
movement may also occur through capillary action and
evapotranspiration (evaporation from open bodies of
water and soil surfaces and the uptake of soil
moisture and release to the atmosphere by plants).
The factors described above are considered important in
evaluating leaching potential at a site based on standard
concepts of water and chemical movement through porous media.
However, recent studies (Hallberg, 1986) indicate that
preferential flow (of water and solutes) through soil
macropores may be a major cause of pesticide leaching to ground
water under various soil and climatic conditions.
Under standard concepts of flow through porous media, sandy
soils should provide a higher potential for pesticide leaching
than clayey soils. However, clayey soils may tend to be well
structured and contain a high number of macropores which may
enhance the potential for rapid leaching. In addition,
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dessication of clayey soils may result in prominent shrinkage
cracks. Rainfall or irrigation, water flowing preferentially
along such features may promote leaching, even when other
pesticide properties and site conditions are not conducive to
leaching.
Appendix C contains a national map prepared by the Soil
Conservation Service of the patterns of soil orders and
suborders of the United States. More detailed local
information on soils is available from State and district
offices of the Soil Conservation Service.
Other Factors .. —
Several other factors also affect pesticide leaching
potential and the likelihood for ground water contamination.
Depth to ground water and permeability of the material in the
vadose (unsaturated) zone are considered particularly important
in determining vulnerability to pesticide contamination. Areas
of karstic hydrogeologic conditions, found in many regions of
the United States are also particularly vulnerable to
contamination. Hydrogeologic information may be available from
State geological survey offices and/or district offices of the
U.S. Geological Survey in some areas of the country. Well
drilling logs are another possible source of information,
although they tend to be of inconsistent quality.
The amount and seasonal variation in the amount of
recharge—rainfall and irrigation—is another important factor
influencing leaching potential. Areas with high rates of
infiltration from rainfall or irrigation water have large
amounts of water passing through the soil, and therefore are
more susceptible to leaching. Average monthly precipitation
data are recorded at numerous stations around the country and
are available from several publications, including van der
Leeden and Troise (1974). Several methods of calculating
evaporation and evapotranspiration are given in Dunne and
Leopold (1978). One of the more common methods is the
Thornthwaite method, which uses air temperature as an index of
the energy available for evapotranspiration. Average monthly
air temperature for numerous stations is also available from
van der Leeden and Troise (1974).
Man-made site features such as poorly constructed water
supply wells, agricultural drainage wells, and faulty check
valves on chemigation systems also influence whether a
pesticide will reach ground water. These features can lead to
"short circuiting" or the creation of pathways for pesticides
to enter ground water without filtering though soil.
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CHAPTER THREE
OBJECTIVES OF MITIGATION MEASURES TO REDUCE
PESTICIDE CONTAMINATION OF GROUND WATER
Since site conditions, pest and crop patterns, and
agricultural practices vary widely, no specific recommendations
for practices to reduce the risk of pesticide contamination can
be developed that are appropriate for all situations.
Generally, however, measures to protect ground water from
pesticides achieve one or more of the following objectives:
--Reduction of the quantity of pesticides used.
--Use of pesticides with less potential to leach.
--Avoidance of pesticide application when conditions are
most likely to promote leacning.
--Prevention of spills and elimination of pathways for
entry of pesticides to ground water.
Tne potential impacts on leaching of various farming,
pesticide application, irrigation, and other agricultural
practices are discussed in detail in Part II of this report,
along with suggestions for measures that can be taken with each
practice to minimize leaching. Many agricultural practices are
"fixed";* that is, they are either impractical to change or
serve another important environmental purpose such as reducing
soil erosion or surface runoff. Other practices are
"variable"; that is, they are more amenable to cnanges in
management such as timing or rate of pesticide application.
Designing a program to promote tne use of good practices to
reduce pesticide contamination risks requires an understanding
of the type(s) of agriculture and agricultural practices that
are common or typical in the area. This knowledge forms the
basis for identifying specific practices that might be promoted
as well as the particular technical assistance needs of tne
area's agricultural producers.
* No practice is ever completely "fixed," since there is always
the potential to change crops, tillage equipment, etc. The
term is used because of the major investment likely to be
involved in changing or because they are in place to achieve
other important benefits.
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An obvious part of any plan to reduce the potential for
leaching of pesticides into ground water is minimizing the
r
I-
integrated pest management (IPM) system.
IPM is an integrated approach to pest control that involves
pe
Case studies have shown that pesticide use can e greatly
?
tha? inKuence those pests; and after considering the concepts,
Extension specialists or pest consultants.
Using Pesticides with Lower beaching Potential
As described in Chapter Two, studies have shown that
rthe^o^enLKlorlharpestlcide to leach
. NumerouS pesticides have been proven
I
with lower leaching potential should be encouraged,
particularly in areas with vulnerable conditions.
Reducing Pesticide Application at Times Most i^exy
Promote Leaching
While many of the site conditions conducive to leaching are
natural? occurring, various farming and irrigation practices
-15-
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can increase or decrease the likelihood that pesticides will
leach. When soils are at or near saturation or have many
macropores or cracks, conditions are particularly conducive to
leaching.
Some farming practices can help reduce the potential for
pesticide leaching by enhancing the soil's ability to retain
moisture or adsorb or degrade pesticides. Other practices,
however, may promote leaching. Ponding of runoff water high in
pesticides may promote infiltration into the ground. Certain
tillage practices may foster the formation of macropores which
enhance infiltration. Chapter Five in Part II describes the
impact of a variety of tillage and other farming practices on
leaching.
The method and timing of irrigation and pesticide
application can also create site conditions that are conducive
to pesticide leaching. With some irrigation methods, soils are
kept at or near full saturation. This condition can promote
pesticide leaching when normally adsorbed pesticides desorb
from soil particles and become available to leach into ground
water. In addition, improper and/or excessive irrigation can
promote leaching of surface-applied or soil-incorporated
pesticides by moving dissolved pesticides through soil. The
potential impact of various irrigation methods and timing of
pesticide applications are discussed in Chapter Four of Part II
In many areas of the United States,, site conditions may be
conducive to leaching either naturally or as a result of
irrigation. In general, site conditions that are conducive to
leaching occur when ground-water recharge rates are high and
significant guantities of water move downward. This can occur
in areas where infiltration is significantly higher than
evapotranspiration, and/or where soils are highly permeable.
This is particularly a problem in irrigated semi-arid or arid
regions of the United States where infiltration of irrigation
water leaching from agricultural fields is the primary source
of ground-water recharge. High ground-water recharge rates
alone, however, do not necessarily indicate that concentrations
of pesticides will reach levels of concern because the
pesticides may be sorbed to soil or degraded before reaching
ground water.
Preventing Accidents, Spills, and Pathways for Pesticides
to Reach Ground Water
Contamination of ground water can also be avoided by proper
pesticide handling and by eliminating pathways for pesticides
to enter ground water from the ground surface or from surface
water. Contamination by any pesticide, regardless of its
leaching potential, can result from spills and leaks or entry
by direct pathways.
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In the steps between the purchase and application of
pesticides, pesticides may be spilled or released into the
environment at any time or place during transport, storage or
handling. Depending on site conditions and the amount of
pesticide involved, movement of the released pesticide to
ground-water can occur. Ground water contamination is a
particular concern if spilled pesticides build up in soil, sucn
as can happen if application equipment is loaded or cleaned in
one designated area repeatedly. Careful storage and handling
of pesticides can help to minimize spillage and waste.
Improperly constructed or abandoned irrigation or drinking
water wells can provide a direct pathway for pesticides to
enter ground water. In ungrouted wells, especially those
located in topographic depressions susceptible to surface
runoff, water may be able to run down the outside (or even the
inside) of the well casing directly into ground-water
supplies. In addition, pesticide-laden surface runoff water
may enter ground water through abandoned wells that are not
sealed properly or covered. Pesticides may also enter ground
water via irrigation wells connected to chemigation systems
unequipped with check valves to prevent back-siphoning of
chemicals into the well.
In developing measures to reduce the impacts of pesticides,
the relationship between ground water and surface water should
also be considered. Surface water bodies that are susceptible
to runoff from agricultural fields, such as irrigation reuse
pits or farm ponds, may contain high amounts of pesticides.
Although such surface water bodies may not serve as direct
sources of drinking water, they may recharge ground-water
supplies. Futhermore, where ground water discharges to surface
water, it is possible for any ground water that is contaminated
with pesticides to adversely impact surface water supplies.
Measures to avoid contamination from leaks and spills and
to reduce direct pathways for contamination are discussed in
Chapter Seven of Part II.
Selecting Combinations of Practices
While the broad objectives described in tnis chapter set
forth an overall framework for reducing the risk of pesticide
contamination from crop production, determining which practices
can and should be promoted involves analysis of the particular
conditions, needs, and capabilities of farms in the area of
concern. Design of specific measures may ultimately need to be
done at the individual farm level. Technical assistance in
determining appropriate measures is available from a variety of
agencies (see Appendix D) .
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In the development and external review of this report one
overriding recommendation emerged thajt_Js__apprnpriat-p fnr 311
_
conditionsj £esticide_use_should be reducedtoonlT'that which
is essential. While biological methods of~^esT control have
not yet been developed for all crop and pest situations, the
principles of integrated pest management, which include a
variety of chemical, biological, and non-chemical methods,
should be applied to the extent feasible. Reducing pesticide
use protects not only ground water, but also the environment in
general—and particularly, the farm family and farm community.
Reduced chemical inputs can also improve farm profitability,
and may help in addressing the increasing pest resistance
problem.
Selection of appropriate measures is influenced to a large
extent by the topography and soil type of the site. For
example, flat fields of sandy soils with low adsorptive
capacity and high permeability, where ground-water is recharged
primarily from infiltration of irrigation water, require
specific mitigation measures. In such cases, one should
concentrate on reducing the quantity of pesticides used,
carefully managing water use, timing applications for when site
conditions are less likely to promote leaching, and increasing
the ability of the soil to adsorb and/or degrade pesticides.
By contrast, for a hilly site with clay-rich soils of low
permeability and high adsorbtive capacity, where the ground
water is generally of low vulnerability to contamination,
practices to reduce soil erosion and control surface runoff are
likely to be in place. Here, leaching is less likely, so
mitigation^would focus on other pathways to ground-water. For
these settings, mitigation measures should concentrate on
reducing the quantity of pesticide used (so that both surface
and ground-water are protected) and minimizing the potential
for pathways such as farm ponds and irrigation re-use pits to
adversely affect ground water.
In Part II, the potential impact on ground water of a wide
range of agricultural practices is discussed in detail. The
information is presented to suggest possible measures that,
when tailored to local conditions, can be incorporated into
ground-water protection efforts. Appendix D contains a
description of agencies and organizations with expertise in
agriculture, soil science, and hydrogeology who can provide
more detailed information on conditions and practices on a more
localized level.
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PART II
POTENTIAL IMPACT OF
AGRICULTURAL PRACTICES
ON PESTICIDE CONTAMINATION
OF GROUND WATER
This part contains discussions of the potential impact of
pesticide application, farming, irrigation, and other practices
on pesticide contamination of groundwater. Each section
separates "fixed" practices, which are impractical_to change or
otherwise essential, from "variable" practices, which are more
amenable to change to accomplish ground water protection
(and/or other) objectives. Note that no practice is ever
completely "fixed"; the term is used because of the major
investment likely to be involved in changing or because such
practices are in place to achieve other important benefits.
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CHAPTER FOUR
PESTICIDE APPLICATION FACTORS
A carefully adopted plan for pest management can play a
significant role in helping reduce the potential for pesticide
leaching to ground water. Tne plan should include choosing the
most appropriate pest control method. Whenever possible/
consider factors such as: choosing a pesticide with low
leaching potential; properly timing pesticide application
relative to climate, crop stage, and weed and insect
populations; controlling the volume and frequency of
application; and using the correct form of pesticide.
Potential impacts of these factors on pesticide leaching are
discussed individually in the sections that follow.
Fixed Practices
The method of application is generally considered a fixed
practice because it is dependent upon the equipment available
to the farmer and is specific to the type of crop and the type
of pest being treated.
Application Methods
The method of pesticide application refers to how the
pesticide is applied on the crop or field. A pesticide can be
applied to a crop by aerial application, ground application, or
through chemigation. Ways in which the method of application
can impact pesticide leaching to ground water are described
below.
Aerial Application
Aerial application involves the foliar or surface appli-
cation of pesticides from a small airplane or helicopter.
Pesticides applied by this method may not always be applied
uniformly over a field and can drift away from the target site
to nearby fields or surface water. Localized areas may receive
more or less of the application of pesticides, which can result
in over-concentrated areas from which pesticides may leach.
Aerial application of pesticides, however, is often the
only available method, such as at times of advanced crop stages
when ground application is not feasible. Methods that may be
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used to increase the uniformity of application and decrease
drift include applying pesticides only at times when winds are
calm, applying the pesticides at as low an altitude as
possible, using swath analysis to evaluate distribution, and
adjusting spray nozzles and drop sizes to account for air
turbulence (propwash) (Maas, et al, 1984).
Ground Application
Ground application involves applying pesticides through
land based vehicles. Pesticides applied by ground application
can be foliar applied, surface applied, or soil incorporated.
With foliar applied pesticides, the quantity of pesti-
cides used can be reduced by adjusting spray drop sizes
relative to the surface of the plant to which they are being
applied. This helps pesticides stick to plant surfaces and not
run off onto soil. The drop sizes should be small enough to
avoid runoff, but not so small that they are susceptible to
drift and inadequately cover plant surfaces (Roberts, 1982).
The quantities of pesticides used can also be reduced
through the use of methods that help foliar applied pesti-
cides cling to plant surfaces, such as by adding crop oil or
surfactants to the pesticide mixture. Electrostatic sprayers,
or sprayers that use ultra-low volumes of pesticides by
recirculating pesticides that do not become attached to the
plant surface, are also effective. With electrostatic
sprayers, pesticide drops are negatively charged before they
are applied to plant surfaces. The negatively charged pesti-
cide can then more easily attach to the positively charged
surfaces of the plant. In some sprayers, the negatively
charged pesticides that do not attach to plant surfaces can be
collected and recirculated, thus reducing the quantities of
pesticide used (Mass, et al, 1984).
The potential for pesticide leaching to ground water is
higher with surface applied and soil incorporated pesticides
an for foliar applied pesticides. This is particularly true if
the pesticide is applied where site conditions are most
conducive to leaching. However, for many insects and weeds,
surface application or soil incorporation are the only
effective means of control. In irrigated agriculture, the
potential for pesticide leaching with these application methods
depends, in large part, on the method of irrigation being used
(See Chapter Six).
Where surface application and/or soil incorporation is
necessary, uneven application of the pesticide can cause an
increase in the potential for pesticide leaching. The
uniformity of the application depends, in part, on the
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uniformity, calibration, spacing, and height of the nozzles
(Roberts, 1982). Improper calibration can lead to concen-
trated bands of pesticide.
Chemiqation
Chemigation involves mixing the pesticide with water
flowing through an irrigation system. The irrigation system
used is most often a spray or drip system, although chemigation
can also be practiced with flood irrigation. The potential
impacts of chemigation on pesticide leaching are discussed in
Chapter Six.
Variable Practices
By choosing appropriate pest control methods and carefully
managing the amount, volume, and timing of pesticide
applications, the risk of ground water contamination can be
reduced significantly.
Choice of Pest Control Method
Subsequent sections describe many ways to control pest
populations through management practices that either eliminate
or reduce the need for pesticides. Further, an overall
recommendation regarding the use of pesticides is to implement
integrated pest management (IPM) techniques, which consider
non-chemical methods of pest control and prescribe the use of
pesticides only as they are needed to keep pest populations
below economic thresholds (see discussion of IPM in
Chapter Five). Reductions in the use of pesticides will result
in the greatest protection for all environmental media.
Selection of Pesticide
When use of a pesticide is necessary to control damaging
pest populations, careful selection can help avoid
contamination of ground water. As described in Chapters Two
and Three, persistent pesticides with high water solubility
that do not adsorb readily to soil have the highest potential
to leach. Table 2-2 (Page 11) lists the pesticides EPA has
determined as having greatest potential to leach based on
current data and understanding. The Agency will monitor these
pesticides in the National Survey of Pesticides in Well Water.
Until better information is available, this list represents the
pesticides for which there is some concern that they may leach
to ground water as a result of normal application to the land.
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Form of Pesticide
The form of pesticide can affect the potential for leaching
into ground water. Pesticide forms include powders, dusts,
granules, timed-release encapsulated forms, concentrated
emulsions, liquid concentrates, and aqueous solutions. The
particular form used is generally dictated by the pesticidal
effect desired.
Different spraying formulations may be prepared by
dissolving a solid in water, by mixing a liquid solution with
water, by mixing a wettable powder to form a suspension, by
mixing an emulsifiable concentrate with water to form an
emulsion, or by mixing an oil-miscible formulation with an
oil. All these forms of application have variable impacts on
the leaching potential of pesticides. For example, surfactants
made of oils are added to foliar-applied herbicide/insecticide
sprays to increase the penetration and translocation of the
chemicals within the plant tissue. This process increases the
effectiveness of the pesticide, thus allowing a smaller
application of the active ingredient. These additives also
help the pesticide stick to the plant surfaces, thus reducing
the amount washed off onto the soil and the potential for
leaching to ground water. However, the surfactants may
increase the potential for pesticide leaching of washed off
pesticides by decreasing their ability to adsorb to soil
particles.
Pesticide solubility can also impact leaching potential.
Pesticides with low solubility and high adsorbtive capacity are
prone to be transported in the sediment phase rather than in
dissolved runoff and thus have lower potential to leach. More
soluble pesticides can be carried to ground water in solution
where runoff is not significant.
Because of their high solubilities, wettable powders,
dusts, and microgranules are generally susceptible to surface
runoff or to leaching. These solid forms of pesticides also do
not volatilize as readily as do pesticides in liquid and
aqueous solutions and may persist in soil, potentially
affording more time when leaching might occur.
Application Timing
The time that a pesticide is applied can be a major factor
in pesticide leaching potential, depending on local environ-
mental conditions, temperature, and rainfall. Leaching
potential is minimized when the applied pesticide is fully
utilized or when the soil conditions promote degradation.
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Timing of pesticidal application should be relative to climatic
conditions, crop stage, and weed and insect populations.
Figure 4-1 presents, for illustration purposes, a summary of
the concepts presented in this discussion; note that actual
timing decisions will vary based on climate, crop, and pest
control needs.
Climatic Conditions
The degree of pesticide leaching at a particular site
depends on the amount and nature (e.g., drizzle vs. downpour)
of local precipitation events. The temperature of the soil and
surrounding air at a site can also greatly affect the processes
that result in a pesticide's movement and degradation in the
environment. These climatic factors are governed by the season
and the geographical location. In general, pesticides are more
likely to leach below the root zone when the soil is at or near
full saturation after heavy precipitation. This condition can
result in pesticide desorption from soil particles, or downward
movement of dissolved pesticides. As such, leaching can be
minimized by limiting pesticide application during wet
seasons. Leaching potential can also be minimized by observing
weather patterns and avoiding pesticide application before
major precipitation events. In either situation, proper timing
of pesticide application relative to climatic conditions
involves knowledge or understanding of the period(s) of heavy
precipitation for the geographical area in general (e.g., late
spring or fall). The immediate weather forecast, is, of
course, of primary importance in making a specific application
decision.
Crop Stage
Pesticides are usually applied at pre-planting, at
pre-emergence, or during post-emergence. Pesticides applied
during pre-planting and pre-emergence stages have higher
potentials to leach than those applied post-emergence. The
potential for post-emergent applied pesticides to leach depends
upon the crop stage. In general, mature crops have a higher
capacity for uptake of pesticides. During this stage of crop
growth, water is absorbed at the root zone, thus limiting
downward movement of water and the potential for pesticide
leaching. For some weeds and pests, however, the benefits of
pre-plant and pre-emergent application may outweigh the higher
potentials for leaching associated with these methods. This
would be true when, for example, a single application per
season is effective in controlling weeds that would otherwise
require multiple applications.
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I
NJ
Ln
150-
140-
130-
120-
110-
I
t 100-
S 90-
2 M-
UJ
I 70"l
I 60-|
WJ o
> 50-
40
30
20
10
CROP GROWTH
CRITICAL WEED GROWTH- /
FIRST CYCLE \ '
CRITICAL PERIOD FOR
POST-EMERGENCE
PESTICIDE APPLICATION^,
APR
CRITICAL WEED GROWTH-
SECOND CYCLE
CRITICAL PERIOD FOR
POST-EMERGENCE
PESTICIDE APPLICATION
/ ^CRITICAL PERIOD FOR
/ PRE PLANT OR
/ PRE-EMERGENCE
/ PESTICIDE APPLICATION
SEP OCT
MONTH OF YEAR
•CRITICAL PERIOD FOR
PRE PLANT OR
PRE EMERGENCE
PESTICIDE APPLICATION
CRITICAL WEED GROWTH-
THIRD CYCLE
DEC
CRITICAL PERIOD FOR
POST-EMERGENCE
PESTICIDE APPLICATION
150
140
130
120
110
100
90
so
70
-60
50
-40
-30
-20
-10
_L
>
<
D
FIGURE 4-1
PESTICIDE APPLICATION RELATIVE TO CROP
GROWTH STAGE, WEED AND PEST OCCURRENCE
(ILLATION ONLY; ACTUAL WILL VARY BASED ON
CLIMATE CROP AND PEST CONTROL NEEDS)
-------
For post-emergent application, the timing of pesticide
application relative to crop stage should consider the inter-
action between growth stages of the crop and the time that the
pest species does the most damage. Many pests cause damage to
crops only during a specific period of the crop cycle (Maas, et
al, 1984). The alfalfa seed-crop, for example, can be best
protected from the lygus bug, which attacks alfalfa buds,
floral parts, and immature seeds, by application of insecticide
during the early bud stage of the crop (Martin and Leonard,
1967). In addition, pesticide application can be reduced by
eliminating application at crop stages where pests do not feed
on the crop. For example, the tobacco budworm, which only
affects buds, cannot cause economic damage to tobacco after
plant leaves emerge, thus eliminating the need for insecticide
application after that point (Maas, et al, 1984).
Thresholds and Pest Cycles
Pesticide application can be reduced through insect and
weed scouting and by being aware of economic thresholds—that
is, the levels at which pest numbers become economically
injurious to crops. Proper timing of pesticide application
relative to economic thresholds and pest cycles can
significantly reduce the quantity of pesticides applied. With
the new pest resistant varieties on the market, most crops can
generally tolerate a high number of pests before yields and/or
crop quality are affected. In addition, many weeds and insects
reach critical growth stages where their numbers can be
drastically reduced with a relatively low amount of
pesticides. Extension specialists with expertise in weed and
insect monitoring can provide advice on proper timing of
pesticide applications.
In several studies, pesticides were found to have been
applied unnecessarily at times when pest scouting indicated
that economic thresholds had not been reached (Maas, et al,
1984). A four-county study in Illinois found that 19 and 11
percent of corn acreage actually required insecticide usage
while 67 and 57 percent, respectively, received it (Luckman,
1978). In addition, a three-year study in the Midwest showed
that only 9 percent of corn fields even contained wireworm, a
commonly treated pest, and only 1.2 percent actually had
wireworm damage (National Science Foundation, 1975). Studies
with soybeans have shown that this crop can have a remarkably
high ability to tolerate insects without significant loss of
yield (Newsom, 1978), thus requiring the use of only small
quantities of pesticides.
Application of pesticides relative to pest growth cycles
can also be useful in reducing the quantities of pesticides
used. The times in pest cycles where they can be best
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controlled can be identified with the help of Extension
specialists, by consulting pesticide label directions, or from
the reports "Weed Control Manual and Herbicide Guide" and
"Insect Product Guide" (published by Ag Consultant and
Fieldman, respectively). For example, Canada thistles and many
broadleaf weeds in corn fields can be effectively controlled
only by applying herbicides in early weed or pre-emergent
stages (Ag Consultant, 1986). In fact, nearly all weeds can be
most effectively controlled by application of pesticides at
times early in growth stages when they are most susceptible.
In addition, pests such as cutworm, corn earworm, cottom
bollworm, sorghum headworm, soybean podworm, tobacco budworm,
and tomato fruit worm are best controlled when the larvae first
appear (Ag Consultant, 1986).
Application Rate and Volume
Proper choice of pest control method and application timing
can reduce the quantity of required pesticides as described in
the previous sections. In addition, other measures help assure
the most effective use of minimum amounts of pesticides,
including proper maintenance and calibration of pesticide
application equipment, consideration of recommended ranges of
pesticides, and band application of pesticides.
Proper Mixing
Label directions for mixing the pesticide should be
carefully followed to assure the most efficient use.
Under-dilution of the pesticide will result in use of excessive
quantities; more pesticide may be available to leach since
normal degradation processes are likely to be less effective.
Equipment Maintenance and Calibration
Pesticide application equipment should be maintained and
properly calibrated to ensure even application of pesticides
and to ensure that pesticides are applied at volumes intended
by the user. Poorly maintained and/or calibrated equipment can
discharge excessive quantities of an improperly diluted mixture
of pesticides which can result in inefficient use and subse-
quent leaching into ground water. Ensuring the proper rate and
volume of pesticide application can be made easier with the use
of automatic volume regulating devices which cause spray
pressure to vary accordingly with change in speed of the
application equipment.
Pesticide application equipment should be maintained and
calibrated on a periodic basis to achieve the desired
application rates and volumes. The Agricultural Training Board
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of England recommends that calibration should take place at the
beginning of each season; after every 100 hectares sprayed; and
after changes of tractor wheels, nozzles, or pressure (Roberts,
1982).
Detailed information on calibration procedures can be
obtained from Extension specialists and equipment
manufacturers. The calibration procedure for spray equipment
should first include selecting nozzles to give the required
application rate at the intended pressure and speed, based on
the label instructions of the pesticide being applied. The
sprayer should then be adjusted to the intended spray pressure,
and the nozzles should be checked for visual alignment. All
worn or bent nozzles should be repaired or replaced. The
nozzle output should then be checked for uniformity with
flow-measuring devices or by recording the time it takes each
nozzle to fill a container to a specified depth. In a trial
run with the pesticide application equipment filled with water,
the spray width of the nozzles should be checked for the
desired width. If the desired width is not obtained, the boom
height or nozzles can be adjusted accordingly.
Consideration of Dosage Recommendations
Pesticide label instructions recommend a specific dosage,
which is generally expressed in a range of active ingredients
per acre. If pest numbers are relatively low, the lower end of
the recommended range may give adequate results while resulting
in lower quantities of pesticide used. It is illegal to use
greater than the maximum dose shown on the label.
Band Application
Applying pesticides in a band on crop rows rather than on
the entire field is an effective method for reducing the amount
of pesticides used. Band application with corn, for example,
can be used to apply pesticides along the crop row at the time
of planting with a sprayer located behind the planter. Drop
nozzles can also be used to spray below the crop canopy,
allowing use of less pesticide and more effective application.
The band application will control weeds along the row, while
mechanical cultivation or lesser amounts of pesticides can be
used to control weeds between the rows (Martin and Leonard,
1967).
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CHAPTER FIVE
FARMING PRACTICES
Farming practices can help reduce the quantities of
pesticides used and make site conditions less conducive to
leaching. Farming practices employed at a given farm are
usually influenced by soil conditions, topography, rainfall
pattern, cropping pattern, economic status of the farmer, and
individual knowledge of various agricultural practices. A
combination of farming practices can be used to set up an
integrated pest management (IPM) system, in which the
quantities of pesticides used can be greatly reduced.
Many farming practices are also used for the purposes of
preventing soil erosion and surface runoff. Because in some
situations there may be tradeoffs, the choice of farming
practices should consider impacts on all environmental media.
For example, one farming practice may be useful in reducing the
leaching potential of pesticides, but may promote soil erosion,
with subsequent negative impacts on surface water quality.
Fixed Practices
Since different tillage methods require different types of
capital equipment and are often selected as a means for
controlling erosion and surface runoff, tillage practices are
considered, for this publication, to be "fixed" practices.
When a decision to change tillage method is being made,
however, the potential impact of alternative methods on both
ground and surface water should be considered.
Tillage Practices
The fundamental purposes of tillage are to: provide a
suitable seedbed, reduce competition from weed growth, and make
conditions in the soil more favorable for crop growth (Martin
and Leonard, 1967). Tillage practices can impact the potential
for pesticide leaching by influencing the quantity of
pesticides used and by making the site more or less conducive
to pesticide leaching. Details of how conventional and
conservation tillage can impact the potential for pesticide
leaching to ground water are discussed below.
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Conventional Tillage
In conventional tillage, land is cultivated mechanically
often in both fall and spring prior to planting for seed bed
preparation. Mechanical cultivation is also one of the oldest
forms of weed control known. In addition to weed control,
cultivation between crop rows provides aeration to crop roots
and can help in reducing insect numbers by exposing insects to
the surface where they can be controlled by natural predators.
Conventional tillage can be effective in the control of weeds
that grow between crop rows before the crop can shade the
ground (Martin and Leonard, 1967).
Herbicide use can be relatively low with conventional
tillage, although herbicides are generally used in conjunction
with mechanical cultivation to control weed competition. In
addition, conventional tillage may be useful in eliminating
macropores and animal burrows through which pesticides can
rapidly infiltrate into ground water.
However, because the soil is left exposed, conventional
tillage can promote soil erosion and surface runoff if
practiced on steep slopes (greater than 3%) without contouring
or terraces. Erosion is particularly a problem in areas of the
United States where steep slopes are combined with soils of
relatively low permeability, and rainfall amounts are high and
occur in high-intensity events (storms).
Conservation Tillage
Conservation tillage is defined as any tillage practice
that leaves at least 30 percent of the soil surface covered
with crop residues after planting (Conservation Technology
Information Center, 1987). Conservation tillage is generally
employed as an inexpensive, effective method for reducing soil
erosion and surface runoff. At the present time, considerable
controversy exists over the impact of conservation tillage on
ground water.
The term conservation tillage encompasses five basic
methods: no-till, ridge-till, strip-till, mulch-till, and
reduced-till. With no-till, the soil is left undisturbed prior
to planting, and the planting is completed in a narrow
seedbed. With ridge-till and strip-till, the soil is left
undisturbed prior to planting, although a portion of the soil
surface is tilled at planting. With ridge-till, however,
planting is completed on ridges which are higher than the row
middles, and cultivation is used to rebuild ridges. In
mulch-till, the total soil surface is disturbed by tillage
prior to planting with tillage tools such as chisels, field
cultivators, discs, sweeps, or blades. Reduced-till refers to
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any conservation tillage practice not covered above. With
conservation tillage practices, weed control is accomplished
with a combination of herbicides and cultivation (Conservation
Technology Information Center, 1987).
The controversy surrounding the effects of conservation
tillage on pesticide leaching centers around the fact that
conservation tillage may require additional herbicides in some
cases, compared to conventional tillage (Maas, et al, 1984)^
However experience has shown that much of the increase is due
to a desire for a hedge against uncertainty. Some producers
are using less herbicides than they did when practicing
conventional tillage, often after they have gained experience
and confidence in the new system. Studies on corn have shown
that more herbicides may be required with reduced tillage
compared to conventional tillage (Hanthorn and Duffy, 1983).
For soybeans, however, only no-till was found to cause an
increase in herbicide usage, while there was no significant
differences in herbicide use between reduced till and
conventional tillage.
Different methods of conservation tillage require different
quantities of herbicide and have different effects on leaching
potential. Generally, it appears that no-till requires the
greatest herbicide usage and may lead to site conditions most
conducive to leaching when compared to other conservation
tillage methods. If no-till is used continuously for several
years on the same land, the likelihood for the presence of soil
macropores is higher than for other conservation tillage
methods, thus increasing the potential for pesticide leaching
(Dick et al., 1986). Ridge-till and mulch-till may generally
require the least amount of herbicides because some mechanical
cultivation is done with these methods.
In some instances, higher amounts of insecticides may also
be required with conservation tillage, compared to conventional
tillage (Smith, et al., 1979). The additional amounts involved
are generally greater for no-till.
Although conservation tillage may require the use of more
pesticides in some cases, the overall impact of this practice
on the potential for pesticide leaching remains unclear.
Studies have also shown that conservation tillage, although
sometimes requiring the use of more pesticides, can also help
in reducing the potential for pesticide leaching by making site
conditions less conducive to leaching by enhancing
microbiological activity and degradation of pesticides in the
upper three inches of the soil layer (Helling, 1986).
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Contour Farming
Contour farming involves the planting of crops along
contour lines across slopes. Contour farming is effective at
reducing soil erosion by slowing water movement on the soil
surface and allowing for increased infiltration. It is most
effective on fields of moderate slopes (less than 8 percent)
that are free of depressions and gullies. Runoff volumes may be
reduced up to 50 percent depending on crop and soil type (Maas,
et al., 1984) in comparison to other farming practices.
Although contour farming can decrease surface runoff, this
practice can cause ponding of runoff between rows. Subsequent
increases in infiltration may increase the potential for
leaching of soluble pesticides (Maas, et al., 1984).
Terracing
Terraces are ridges and channels constructed across a
slope. They are divided into two general classes—graded
terraces and level terraces. Graded terraces divert water to a
grassed waterway or to some other non-erosive drain. Level
terraces hold water on the field, thereby increasing
infiltration water and allowing redeposition of eroded soil.
Both types of terraces help reduce surface runoff, with the
greatest reductions occurring in dry areas with level terraces
(Maas, et al., 1984).
Increased infiltration from terracing may result in an
increased potential for leaching of pesticides to ground water.
This is due to the minimized surface runoff, which allows more
water to infiltrate into the ground. Level terraces are often
used in semi-arid areas to supplement the general lack of
moisture in the root zone; in such areas the depth to ground
water is greater so the likelihood of pesticides reaching the
water table is reduced.
Contour Stripcropping
Stripcropping consists of alternating rows of the main crop
with strips of either a grain crop, sod, or a legume. It is
effective in controlling surface runoff and soil erosion by
wind and water (Maas, et al., 1984). Stripcropping can also
help in reducing insect, nematode, and weed problems in some
cases, thus reducing the amounts of required pesticides
(National Science Foundation, 1975). Stripcropping also helps
reduce the total area of land to which pesticides are applied,
thus reducing the quantity of pesticide used.
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Cover Crops
The purpose of cover crops is to provide vegetative cover
to the soil to control soil erosion during the non-growing
season. Insecticide requirements are generally unchanged from
those with conventional tillage, although with no-till, a
contact herbicide may be required to kill the cover crop
(Smith, et al., 1979).
Variable Practices
Farming involves making a large number of choices regarding
where, when, and how crops are planted and harvested; the
variety of plants to be grown; and pest management. Depending
upon the tillage practices used, such variable practices can
have different impacts on the quantities of pesticides used,
and thus, the amount that might be available to leach. Table
5-1 shows the possible impacts of each variable practice on
insecticide and herbicide use when practiced with each of the
fixed practices. The table shows whether pesticide use would
likely increase or decrease as compared to not employing the
particular variable practice.
Crop Rotation
Crop rotation involves periodically changing the crops
grown on a particular area. This practice can reduce the
quantities of pesticide used when practiced with any of the
tillage methods. In addition, crop rotation can help to
improve soil structure, organic matter content, and
infiltration, thereby making conditions more favorable for crop
growth (Smith, et al., 1979). The principle behind crop
rotation and pest control is to eliminate insect pests of a
specific crop by introducing non-host crops into the crop
rotation program. Crop rotation is most effective in reducing
numbers of pests that are poor competitors and have low
survivability and mobility.
Crop rotation has proven to be especially effective against
corn rootworm. Corn rootworm numbers have been found to be
dramatically reduced by rotating crops with corn on consecutive
years (Maas, et al., 1984). Crop rotation has also proven
useful in controlling nematodes and billbugs in wheat (Martin
and Leonard, 1967).
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TABLE 5-1: POSSIBLE EFFECTS OF FARMING FACTORS ON QUANTITIES OF PESTICIDES USED*
I
OJ
Practice
Crop Rotation
Contour Stnpcropping
Cover Crops
Pest Resistant Varieties
Adjusting Planting and
Harvest Times
IPM
Conservation
Other
Conventional
Tillage
In
D/3
D/2
N
D/2
D/2
D/3
H
D/l
D/2
N
N
D/l
D/l
No-Till
In
D/3
D/2
I/I
D/l
D/l
D/2
H
D/3
D/2
I/I
N
D/3
D/2
Ridge-Till
In
D/3
D/2
N
D/2
D/2
D/2
H
D/2
D/2
N
N
D/l
D/l
Tillage
In
D/3
D/2
N
D/2
D/2
D/2
H
D/l
D/2
N
N
D/2
D/2
In - Insecticide
H - Herbicide
I - Increase
N - No Significant Impact
D - Decrease
1 - Minor Impact
2 - Moderate Impact
3 - Major Impact
* The table bhuws generally whether pesticide use would likely increase or decrease compared to not
employing the practice. The effect on actual amounts used at a given location is dependent on
site-specific conditions.
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Planting Pest-Resistant Varieties
A non-chemical pest control method that is steadily
increasing is the planting of pest-resistant varieties. About
75 percent of the total U.S. acreage is planted with pest- and
disease-resistant crop varieties. Insecticide use in the
United States was significantly reduced between 1971 and 1982
(Maas, et al., 1984), partly due to the use of pest-resistant
varieties. Resistance can help the plant to either inhibit
pest growth or recover from injury inflicted by the pest.
However, to reduce the quantity of pesticides used with
pest-resistant varieties, pest scouting and monitoring are
still necessary to ensure that pesticides are applied only when
pest numbers approach economic thresholds.
Adjusting Planting and Harvesting Times
Planting can often be timed to give crops a competitive
edge over insects and weeds, thus decreasing the requirement
for pesticide use. A study in Wisconsin, for example, showed
that corn planted before weed emergence required minimal use of
herbicides. Herbicides were needed in only two out of ten
locations investigated. The study showed that early crop
canopy, particularly in narrow rows, gave the corn a
competitive advantage over weeds and slowed water movement in
soil, thus reducing the potential for pesticide leaching
(Kogan, 1982).
Adjustments in planting and harvesting times can also help
in reducing damage from insects and the use of insecticides.
Planting as soon as the soil is warm enough to permit rapid
plant growth can help corn to avoid corn borer attack.
Planting of winter wheat late enough for the main brood of
hessian flies to have emerged and died can reduce damage from
these pests (Martin and Leonard, 1967). For soybeans, early
planting is encouraged so that a plant canopy can form before
the flight of second generation moths of the corn earworm
(Maas, et al., 1984).
Timing of harvesting can also reduce the need for
pesticides. Early harvesting, before insects reach economic
thresholds, has proven effective for a variety of pests,
including sugarcane borers, sweet potato weevils, potato tuber
worms, and cabbage loopers (Maas, et al., 1984).
Integrated Pest Management
All farming practices discussed above can be incorporated
into an integrated pest management (IPM) system of controlling
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pests with minimal use of pesticides. IPM is a pest control
strategy that utilizes appropriate control methods to keep pest
populations below economic thresholds with the least
undesirable impacts on the environment. It includes both
chemical and non-chemical means of pest control.
Practicing IPM can reduce the overall quantities of
pesticides used, leading to a decreased potential for pesti-
cide leaching to ground water and transport to other environ-
mental media. It has been estimated that a 40 percent reduc-
tion in current pesticide use may result from IPM programs that
are now available, with an estimated projection to a 60 percent
reduction in the next decade by continuing these programs
(USDA, 1985).
An effective IPM system requires extensive knowledge of the
ecology of the system of interest (Maas, et al., 1984) and
generally will require the use of Extension specialists or pest
consultants. One text that includes discussion of IPM (van der
Bosch, 1978) suggests the following general guidelines for
setting up an IPM system:
1) Understand the biology of the crop, and how it is
influenced by the surrounding ecosystem.
2) Identify the key pests; know their biology; recognize
the kind of damage they inflict; and initiate studies
on the economic impact of these damages.
3) Identify the key environmental factors that impinge
upon the pest.
4) Consider concepts, methods, and materials that
individually or in combination will help suppress
permanently or restrain pest species.
5) Structure IPM programs so that they will have the
flexibility needed to adjust to ecosystem changes.
6) Anticipate unforeseen developments; expect setbacks;
move with caution; and remain aware of the ecosystem
complexity.
7) Seek the weak links in the key pest life cycle and
narrowly direct control practices at these weak links,
avoiding broad ecosystem impacts.
8) Whenever possible, use methods that preserve,
complement, and augment biotic and physical mortal-
ity factors of the pest.
9) Whenever feasible, attempt to diversify the ecosystem.
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IPM systems for reducing pesticide use have proven
effective for a number of crops including corn, soybeans, and
cotton (Maas et al., 1984). Crop rotation has been combined
with pest scouting and monitoring to help eliminate corn
rootworm beetle populations (Luckman, 1978). Monitoring and
scouting, optimal planting dates, natural control agents,
resistant varieties, trap crops, selective use of insecti-
cides, and treatments based on economic thresholds have proven
effective for controlling pests (Rudd, et al., 1980).
Note- At present, IPM methods for insect pest control,
while still not available for all crops and all pests, are
generally more developed than for weed control. Since many of
the commonly used herbicides are considered to have significant
leaching potential, many workshop participants and reviewers
from the agricultural and environmental communities noted a
particular need for research to develop IPM methods for weed
control.
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CHAPTER SIX
IRRIGATION PRACTICES
Irrigation is the practice of applying water to the land to
provide sufficient moisture for crop production. Irrigation is
needed because rainfall is either insufficient for crop needs
or does not occur at the ideal time during the growing season.
Proper use of irrigation can increase crop yields and quality
by counteracting high or low temperatures, eliminating short
droughts, and aiding germination and continuous plant growth
(Soil Conservation Service, 1983).
A proper irrigation strategy can also help to make site
conditions less conducive to pesticide leaching and help reduce
the quantities of pesticides used. The goals of the strategy
are to apply pesticides when site conditions are less likely to
promote leaching and to ensure the most efficient use of the
pesticides.
With all methods of irrigation, water inputs should be
managed to limit the potential for pesticide leaching (Helling,
1986). Water conservation practices, such as the use of soil
moisture monitors to determine field water requirements, will
help avoid over-watering and minimize the potential for
dissolved chemicals to leach with the excess water.
Irrigation practices that can influence the potential for
pesticides to leach to ground water include the method of
irrigation (fixed practice) and the timing, volume, and
frequency of irrigation (variable practices). The potential
for pesticides to leach is also dependent upon the relationship
between the method of irrigation and the method of pesticide
application (See Chapter Four). Table 6-1 shows the potential
for pesticide leaching of various irrigation methods practiced
with various pesticide application practices. For leaching
potentials listed in Table 6-1, it is assumed that the applied
pesticide has a high potential to leach, based upon its
physio-chemical properties.
Fixed Practices
Methods of Irrigation
Irrigation methods commonly used in commercial agricul-
ture can be categorized generally into three basic types:
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TABLE 6-1: POTENTIAL FOR PESTICIDE LEACHING WITH VARIOUS METHODS
OF IRRIGATION AND PESTICIDE APPLICATION*
I
OJ
Application Method
Foliar Application
Surface Application
Pre-Plant/Emergent
Post Emergent
Soil Incorporated
Pre-Plant/Emergent
Post Emergent
Chenugation
Irrigation Method - Soil Type
Sprinkler Drip
thod Clay
on L
ion
gent L
L
d
gent M
L
Loam
M
M
M
M
M
Sand
M
M
M
H
H
Clay
L
L
L
L
L
Loam
L
L
L
M
M
Sand
L
M
M
M
M
Clay
L
M
M
M
M
Flood
Loam
L
M
M
H
M
Sand
L
H
M
H
H
M
H
M
M
M
H
H
L Low Leaching Potential
M -- Moderate Leaching Potential
H - High Leaching Potential
* The table assumes that a pesticide with chemical-physical properties indicating leaching potential is
being used. Actual leaching potential will depend on the specific pesticide and site properties.
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flood or furrow, sprinkle, and trickle or drip. There are many
variations within these categories and there are other methods
designed for specific crop needs and site conditions. A
growing practice, known as chemigation, is to apply pesticides
and/or fertilizers through the irrigation systems.
Flood or Furrow Irrigation
In this method of irrigation, water is retained within some
type of ridge or dike and infiltrates into the ground in
response to gravity. Water is pumped or allowed to flow from
ground or surface sources into the ridged or diked area. In
level or graded basin irrigation, for example, all or part of
the crop is flooded temporarily until the soil absorbs the
water. In furrow irrigation, water is ponded between crop rows
in furrows created during planting and cultivation (Soil
Conservation Service, 1983). Flood or furrow irrigation may
promote leaching of soil incorporated and surface applied
pesticides because it is difficult to avoid over-application of
water with this method (Helling, 1986). Over-watering may
promote downward movement or desorbtion of pesticides,
particularly where soils are highly permeable.
Sprinkle Irrigation
In sprinkle irrigation, water is sprayed into the air
through perforated pipes or nozzles operated under pressure.
Sprinkle systems can be classified into three broad
categories: portable, solid-set, or self-propelled (Soil
Conservation Service, 1983).
Sprinkle irrigation offers the greatest potential to
promote pesticide leaching when it washes foliar applied
pesticides from crop and weed surfaces before they are
effectively utilized. When foliar applied pesticides are used
with sprinkle irrigation, therefore, proper timing of
irrigation with regard to pesticide application is essential.
Trickle or Drip Irrigation
In trickle irrigation, water is applied slowly on or
beneath the surface layer—usually as drops, tiny streams, or
miniature spray—through emitters or applicators placed along a
water delivery line. Trickle systems are normally designed to
apply light, frequent applications of water and to wet only
part of the soil (Soil Conservation Service, 1983).
Since trickle irrigation is a relatively conservative user
of water, the potential for over-application of water and
subsequent leaching of pesticides can also be relatively low.
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Chemiqation
With chemigation, pesticides (or fertilizers) are mixed
with irrigation water before they are applied to the field, and
irrigation and application is done simultaneously. Chemigation
can be done with any irrigation system and method as long as
the pesticide and the method of application are compatible.
For example, surface applied pesticides should only be applied
with drip or flood irrigation. While it is common practice to
irrigate at the same time as pesticide application, some
experts recommend that only the amount of water needed to
activate the pesticide should be applied when chemigating (see
Irrigation Timing, below).
Although research is limited on this subject, there is some
concern that the practice may promote leaching because the
pesticide (or fertilizer) is being applied continuously or in
pulses when it is already dissolved (Helling, 1986). The
potential impact of chemigation when practiced with drip
irrigation systems, however, may be lower because less water is
used with this method compared with flood and sprinkler_
irrigation, and the pesticide is being applied in localized
areas nearer the crop. Another possible source of ground-water
contamination associated with chemigation is faulty, leaky, or
non-existing anti-back-siphoning devices (see section on
Chemigation Back-Siphoning Devices in Chapter Seven).
Variable Practices
Irrigation Timing
The proper timing of irrigation relative to pesticide
application can enable the pesticides to be utilized most
effectively. Under relatively dry conditions, soil incorpor-
ated or surface applied pesticides will remain in the root zone
or be adsorbed onto soil particles before significant leaching
can occur. However, when excessive water is applied before
pesticides degrade or can be taken up by plants, mobile
pesticides may move with infiltrating irrigation water and
leaching may occur. Because of this possibility, irrigation
should be delayed, when practical, following pesticide
application. The delay time is a function of, among other
factors, the rate of plant uptake of the pesticide and the
pesticide degradation rate.
The rate of plant uptake of soil applied pesticides is
generally a function of the transpiration rate of the plant.
In addition, plant uptake also increases as the root zone depth
increases (Carsel, et al., 1984). Therefore, for post-emergent
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pesticides applied to mature crops, a shorter delay time is
necessary than for post-emergent pesticides applied to young
plants or pre-emergent or pre-plant applied pesticides. The
necessary delay time is also shorter for pesticides with faster
degradation rates in soil, which is an inverse function of the
pesticide half-life. Appendix B shows degradation rates for
selected pesticides in soil.
For foliar applied pesticides which rely on contact with
the plant surface for effectiveness, sprinkle irrigation too
soon after application may wash pesticide off onto the soil
before the full benefit of the pesticide is obtained. Again,
by delaying irrigation which may wash pesticides from plant
surfaces, the pesticide can be fully utilized and the potential
for pesticide leaching reduced. The delay time between foliar
application and irrigation is generally a function of the
degradation rate of the pesticide on foliage. For pesticides
with short half-lives, the necessary delay time is shorter.
Appendix B shows degradation rates for selected pesticides on
foliage.
Irrigation Volume and Frequency .
As stated earlier, avoiding excess water inputs can be an
effective method of limiting the potential for pesticide
leaching. Studies have shown that fields are often irrigated
at unnecessarily high volumes and frequencies (University of
Nebraska, 1984), and irrigation amounts can almost always be
reduced with no significant impacts on yield.
Irrigation volumes and frequencies can be limited through
soil moisture monitoring and with the help of various water
conserving best management practices (BMPs). Soil moisture
monitoring can be done with portable moisture meters and probes
that indicate soil moisture levels. This practice can help
determine the water requirement in a field and will identify
when water contents become low enough to cause crop stress.
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CHAPTER SEVEN
OTHER PRACTICES TO REDUCE CONTAMINATION POTENTIAL
In many areas of the country, natural hydrogeologic
conditions make pesticide leaching to ground water more likely
to occur than in other areas. Factors that are generally
conducive to pesticide leaching include high ground-water
recharge rates, highly permeable soils, soils with low
capacities to adsorb or biologically degrade pesticides, and
shallow ground water depths. In karst areas, ground water can
also become contaminated by surface water running into
sinkholes.
The potential for pesticides entering ground water can be
increased by man-made alterations to the land such as poorly
constructed, improperly sealed currently used or abandoned
wells, and agricultural drainage wells. The potential can also
be increased from chemigation systems that are improperly
equipped.
This chapter describes actions, not all strictly manage-
ment practices, that can be taken either to minimize the
likelihood of pesticides entering ground water or to minimize
the impact on water supplies if contamination should occur.
Note: Workshop participants and reviewers generally agreed
that the practices described in this chapter should be employed
everywhere, regardless of hydrogeologic vulnerability.
H<
dling and Disposal of Pesticides and Pesticide Productj
Spills and improper disposal of any pesticide, not just
those pesticides considered to have high leaching potential,
can result in ground-water contamination. If a spill or
release occurs, "slugs" of the pesticide can overwhelm normal
decomposition processes and soil adsorption capacity, resulting
in a high potential for pesticide leaching. Careful handling
and disposal of pesticides are critical parts of an overall
effort to reduce the risk of ground water contamination.
Studies in Wisconsin, Iowa, California, North Carolina, and
other states suggest that incidents in which pesticide
concentrations in ground water exceed State standards are often
the result of pesticide spills and leaks during loading,
handling, or storing of pesticides, and from pesticide
equipment rinsing.
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Pesticide storing, mixing, or loading activities should be
conducted as far from wells as possible to prevent
contamination. These activities should take place, whenever
feasible, on an impervious foundation or on a ground cover to
retain spilled materials. The USDA Soil Conservation Service
can provide information to farmers interested in constructing
special facilities for mixing and loading designed to minimize
the potential for ground water contamination. Care should be
taken that storm drains and any routes of runoff from the area
are protected by berms or diking.
Closed-system transfer, mixing, and loading of pesticides
can substantially reduce worker exposure and facilitate
pesticide handling. In these systems the chemical is delivered
through gravity flow, suction, or pumping, thus eliminating the
need to open and handle pesticide containers. Closed systems
meter and transfer pesticide products from shipping container
to mixing or application tanks, and often rinse the emptied
containers as well. Closed systems can also provide greater
accuracy in measuring the dosage, and reduce or eliminate fill
site contamination from spillage. Mechanical failures such as
hose breaks, and backsiphoning into water sources, however, may
occur with these systems, depending on their design and
operation.
Recommendations for pesticide handling have been summarized
by the University of Wisconsin (1987):
1) Open pesticide containers carefully.
2) When adding water to a spray mixer, the hose or pipe
should remain above the level of the mixture at all
times to avoid the possibility of back-siphoning into
the water source. An input line should be submerged
in the mix only when it is equipped with a reliable
anti-siphoning device.
3) If an emulsifier or spreader-sticker is used, it
should be added before the tank is full because these
materials tend to cause foaming.
4) Be careful to avoid overflow and never leave a spray
tank unattended while it is being filled.
5) Always have materials for containing or cleaning up a
spill close at hand. Know ahead of time what to do to
contain a spill of the particular chemical being
used. A spill must be controlled, contained and
cleaned up. Since different chemicals require
different actions, it is a good idea to have on hand
the "Emergency Response Information Sheets" or "Safety
-44-
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Data Sheets" from manufacturers that have them
available. These provide detailed information about
what to do in case of a spill.
Significant ground-water contamination can result if
pesticide containers break from rough handling, weathering,
corrosion, or age. Proper storage can help avoid these
problems. The label instructions for each registered pesti-
cide contain brief but explicit instructions regarding storage
and disposal. Pesticide containers and materials may be stored
ideally in a separate fire-resistant facility on a pallet or^on
a raised impervious or concrete platform. The storage facility
should be hydrologically downgradient and a safe distance from
the drinking water well and any other sensitive areas. Spill
containment measures, such as paving and diking the area, will
prevent releases to the environment. Routine inspection of the
condition of pesticide containers and the storage facility can
minimize the potential for leaks or spills. Additionally,
maintaining an inventory of stored and used pesticides can be
helpful in this regard.
Damage to containers and spills can occur during trans-
portation. Precautions should be taken to avoid such
accidents, for example, by examining the condition of the
containers, fastening containers to prevent shifting and
damage, and protecting against weather conditions.
Steps should be taken to minimize pesticide-related waste
and reduce disposal problems. Reduction in left-over tank
mixes, rinse water, and the number of pesticide containers
requiring disposal will enhance ground water protection
efforts. In all cases, label directions should be followed
exactly. Only the required amount of pesticide solution should
be mixed and equipment must be carefully calibrated. Rinse
water can be sprayed on cultivated fields where feasible and
consistent with label directions. Fresh water can be carried
and used to flush spraying equipment in the field.
Federal law requires triple rinsing of pesticide
containers, or jet-spray cleaning, before disposal (Federal
Insecticide, Fungicide and Rodenticide Act). Rinsed containers
should be stored securely prior to disposal to minimize the
chance of inadvertent exposure to humans or the environment.
Metal containers may be recycled through scrap metal dealers;
those not suitable for recycling or refilling by distributors
should be disposed of in a sanitary landfill.
The potential for pesticide contamination of ground water
may be significantly reduced by employing common sense,
caution, and the methods and procedures discussed above.
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Chemigation Anti-Backsiphoning Devices
A growing practice in many areas of the country is the
application of fertilizers and pesticides through irrigation
systems, often termed "chemigation". Although there are
systems specifically designed for chemigation, in most cases an
existing irrigation system is modified to mix the chemical with
irrigation water for application to crops. Pesticides (or
fertilizers) are generally stored in large tanks located near
wells drawing ground-water for irrigation. Pesticides flow
from the storage tanks into the irrigation water (see Figure
7-1) .
Concerns about pesticide ground-water contamination from
this practice rise from two potential problems: (1) if the
system is not well designed and therefore not operating
properly, the chemical-laden water may be applied unevenly or
at an improper rate, resulting in inefficient use of the
chemical and a greater potential for leaching; and (2)
accidental backflow or siphoning of chemicals into the well may
occur when the irrigation pumping system shuts down
unexpectedly (Schepers and Hoy, 1987).
The importance of careful timing and application of
pesticides and irrigation water in reducing risks of pesticide
contamination due to leaching are discussed in Chapters Four
and Six. Because of the potential for ground-water
contamination from backflow into wells, this section discusses
requirements for anti-backsiphoning equipment on irrigation
systems used for pesticide application.
Many States already require the use of anti-backsiphoning
devices on chemigation systems. The State of Nebraska requires
also that chemigation systems contain inspection ports built
into the chemigation system pipelines to allow visual
inspection of the check valves (State of Nebraska, 1986). In
addition, EPA recently notified pesticide registrants that they
must place specific chemigation use directions on the label of
any pesticide they wish to be eligible for use in such systems.
Unless the pesticide user's equipment meets these EPA label
requirements, it will be a violation of the Federal pesticide
law to use the pesticide in the chemigation system. Labeling
requirements, PR Notice 87-1, for chemigation systems connected
to sprinkler, flood, and drip irrigation systems include:
1) The system must contain a functional check valve,
vacuum relief valve, and low pressure drain appro-
priately located on the irrigation pipeline to prevent
water source contamination from backflow.
-46-
-------
Bickflow
prevention
device
Irrigation pipe lint
trrigttion pump
Check
valvt
should
be property
shielded
Discharge
line
FIGURE 7-1
CHEMIGATION SYSTEM WITH ANTI-BACKSIPHQNING DEVICE
SOURCE: ASAE1980
-47-
-------
2) The pesticide injection pipeline must contain a
functional, automatic, quick-closing check valve to
prevent the flow of fluid back toward the injection
pump.
3) The pesticide injection pipeline must also contain a
functional, normally closed solenoid-operated valve
located on the intake side of the injection pipe and
connected to the system interlock to prevent fluid
from being withdrawn from the supply tank when the
irrigation system is either automatically or manually
shut down.
4) The system must contain functional interlocking
controls to automatically shut off the pesticide
injection pump when the water pump motor stops.
5) The irrigation line or water pump must include a
functional pressure switch, which will stop the water
pump motor when the water pressure decreases to the
point where pesticide distribution is adversely
affected.
Readers who wish to obtain a copy of the EPA labeling
requirements for pesticides to be used in chemigation should
write to the Registration Division, Office of Pesticide
Programs, TS767C, U.S. Environmental Protection Agency,
Washington, D.C. 20460 and refer to PR Notice 87-1.
Buffer-Zone Establishment
A buffer zone is an established area or distance between a
polluting activity (e.g., nonpoint source of entry of
pesticides into ground water) and a point of ground-water
discharge such as a well. The purpose of the buffer zone is to
allow adequate space and/or time for dilution, dispersion, or
degradation of the pesticide before it reaches the ground water
to minimize its potential adverse impacts. The concept of
altering activities to protect the ground water in portions of
the recharge area to a well is fundamental to the new Wellhead
Protection Program established under the 1986 Safe Drinking
Water Act amendments, rthile buffer zones are generally useful,
they protect primarily existing wells, not future or potential
sources of drinking water (some future wells may be located in
wellhead protection areas).
Establishing a buffer zone adequate in size and
configuration to provide protection against pesticides entering
into ground water that supplies a well depends upon a number of
factors. First, pesticides vary in the speed and degree to
-48-
-------
which they degrade in ground water. Also important are
hydrogeologic conditions—such as the depth to ground water,
ground-water flow velocities, ground-water flow patterns,
ground-water recharge rates, aquifer types, recharge and
withdrawal rates, and assimilative capacity of the aquifer. A
larger buffer zone may be required for groundwater that is
particularly vulnerable to contamination. Vulnerable
ground-water resources may include aquifers with shallow ground
water or permeable soils with little or no adsorptive capacity
and/or high recharge rates. In addition, consolidated rock
aquifers that are highly fractured present particular
challenges to protection, in many cases comparible to the karst
problem discussed later. Readers interested in more
information regarding methods for determining size of wellhead
areas (buffer zones) should obtain a copy of "Guidelines for
Delineation of Wellhead Protection Areas," published by the
Office of Ground-Water Protection, U.S.Environmental Protection
Agency, WH-550G, Washington, D.C. 20460.
Drinking water wells most likely to be impacted by
pesticides leaching to ground water are the domestic supply
wells located in rural areas near agricultural fields and
community supply wells where there is a high degree of
interface between agricultural and residential land use. Wells
that are hydrologically downgradient from crop lands have the
greatest potential to be impacted. For private wells at risk
to pesticide contamination, stopping the use of pesticides in
the area around the well can be an effective means of providing
extra protection to current sources of water supply. Of
course, other practices, such as those described in this
report, should be used to protect all other ground water to
help assure its quality for future use.
Many experts recommend that pesticides should not be mixed,
stored, handled, or applied in the immediate vicinity of a well
(e.g., 25 to 50 feet) to avoid direct well contamination and
run-in from the land surface.
Proper Well Sealing and Abandonment
Water wells with improper sealing around the well casings
can provide a direct conduit for pesticides to enter ground
water from the land surface (Exner and Spalding, 1985). If a
well casing is backfilled with gravel, sand, or other permeable
materials, pesticides can run down the side of the casing and
into ground water. Inadequate grouting and sealing can also
lead to contamination of confined aquifers which would
otherwise be protected from surface contaminants. Inadequate
grouting and sealing can be a problem particularly if the well
is located in a topographically low area susceptible to surface
runoff.
-49-
-------
State standards for well construction should be followed.
Generally, to prevent ground-water contamination via improperly
sealed wells, the well should be sealed with bentonite grout or
some other form of relatively impermeable material. In
addition, the well should be sealed with concrete for at least
two feet below ground surface.
As is the case with wells that are inadequately grouted and
sealed, abandoned wells can also provide a direct conduit for
pesticides to reach ground water, particularly if the well is
located in an area susceptible to runoff or chemical spills.
Also, abandoned wells may be used to dispose of chemicals by
parties unaware of the environmental or legal implications.
Although many States have strict codes regarding the
abandonment of wells, these codes are difficult and sometimes
impossible to enforce. Proper well abandonment often requires
pressure grouting and the blocking of casing perforations to
adequately seal off different aquifers and to prevent movement
of water through annular spaces. It may involve removal of the
well casing or the pump above the ground.
Avoiding Sinkholes in Areas of Karst or Subsidence
Karstic hydrogeologic conditions are found in agricul-
tural areas, especially in the midwest and southeastern United
States. Under so called "conduit karst" conditions, ground
water may flow through openings (see Figure 7-2) such as caves,
rather than through porous or highly fractured material as
diffuse flow (Quinlan and Ewers, 1985). In karst areas,
sinkholes may form at the surface allowing runoff water to flow
into ground water in underground conduits (Hallberg and Hoyer,
1982). Subsidence due to excessive ground water extractions
can cause fractures and cracking in the ground, increasing
opportunity for movement of pesticides into ground water.
Sinkholes, when located in areas susceptible to runoff from
agricultural fields, provide a direct path for pesticides to
reach ground water. Also, pesticides entering ground water in
karst areas can travel for long distances with little or no
dilution or attenuation.
Several methods are available to help ensure that pesti-
cide-contaminated surface runoff does not enter sinkholes.
Runoff can be channeled away from the sinkhole; cover crops not
requiring pesticides can be planted around the sinkhole; and
pesticide use in the immediate area of the sinkhole can be
stopped by use of a buffer strip made of grass or non-crop
vegetation.
-50-
-------
FIGURE 7-2
KARSTIC GROUND-WATER CONDITIONS
SOURCE Hallberg. et al. 1984
-51-
-------
Sealing of Agricultural Drainage Wells
Agricultural drainage wells (ADWs) are sometimes used to
drain excess water from fields, particularly during wet
seasons, providing a direct route for pesticides to enter
ground water (Grahm, et. al., 1977). Although installation of
new ADWs is illegal in most States, many old wells still exist.
ADWs are usually located in topographically low areas
susceptible to surface runoff. The wells generally consist of
a cistern or basin to collect water and a well that drains
directly into the ground. Generally, ADWs are found in areas
that have underlying consolidated aquifers with high secondary
porosities. Relatively few are found in unconsolidated
aguifers because those wells frequently clog.
To prevent ground-water contamination from ADWs, new wells
should not be constructed and old wells should be properly
abandoned. Proper abandonment involves removal of old well
casing where possible, overreaming the borehole to greater than
its original diameter, and plugging the boring with impermeable
materials.
Subsurface Drainage and Treatment
Subsurface drains are often used to draw off excess water
from agricultural fields (Hallberg, et. al., 1986). The
drained water is then discharged to surface water or allowed to
drain into ground water through agricultural drainage wells
(see the discussion of ADWs above). When subsurface drainage
contains high concentrations of contaminants, treatment, such
as carbon treatment, may be needed before final discharge of
the drainage water to minimize adverse impacts on either ground
or surface water (Stryk, et. al., 1977).
Tile drains can be used to drain large areas without
disrupting the natural soil structure (Stryk, et. al., 1977).
The tile drains are designed to lower the water table to allow
drainage and cultivation and to improve plant rooting. Tile
drains are used extensively throughout the corn belt States to
improve soil drainage in seasonally or perennially wet soils.
Tile drains help to collect unused or excessive pesticides
applied to a crop land. The leachate may be recycled for use
as irrigation water, or it may be diverted to grass waterways
where soil adsorption and degradation processes can take
place. (Note that some herbicides will kill the grass,
however.)
-52-
-------
Farm Ponds and Irrigation Re-Use Pits
Farm ponds are often constructed on farm facilities by
damming up small streams. These ponds form reservoirs of water
for irrigation, for livestock use, or for fish culture. They
often collect surface runoff which may contain high
concentrations of pesticides. Since the ponds may be deeper
than the water table, the possibility of contaminating adjacent
ground water exists.
A measure to reduce risks that may result from pesticide
contamination of farm ponds is to establish a buffer zone
between the pond and nearby drinking water wells. The potential
for ground water contamination from the ponds can also be
minimized by limiting pesticide use in nearby fields.
Irrigation re-use pits are often built in topographic low
areas adjacent to agricultural fields. The pits are used to
store runoff from fields for re-use as irrigation water.
Because the pits contain direct runoff, the water often con-
tains high concentrations of pesticides.
Lining of irrigation re-use pits with low permeability
clays such as bentonite can help minimize the potential impacts
the pits may have on ground-water quality. In addition,
mitigation measures should also include locating the pits as
far as possible from drinking water wells.
-53-
-------
APPENDIX A
REFERENCES CITED
Ag Consultant. 1986 Weed Control Manual and Herbicide Guide.
Ag Consultant and Fieldman. Willoughby, Ohio. 1986.
American Society of Agricultural Engineers (ASAE).
Safety Devices for Applying Liquid Chemicals Through
Irrigation Systems. Irrigation Management Committee.
Proposed ASAE Engineering Practice. 1980.
Carsel, R. F. , Smith, C. N., Mulkey, L. A., Dean, J. D., and
P. Jowise. Users Manual for the Pesticide Root Zone Model
(PRZM). EPA-60013-84-100. U.S. Environmental Protection
Agency, Office of Research and Development, Athens,
Georgia. 1984.
Conservation Tillage Information Center. 1986. National
Survey of Conservation Tillage Practices. National
Association of Conservation Districts, Washington, D.C.
1987.
Dick, W. A., W. M. Edwards, and F. Haghiri. Water Movement
Through Soil to Which No-Tillage Cropping Practices Have
Been Applied. Proceedings of the Agricultural Impacts on
Ground Water Conference. National Water Well Association,
Dublin, Ohio. 1986.
Dunne, Thomas, and L. B. Leopold. Water in Environmental
Planning. W. H. Freeman and Company, San Francisco,
California. 1978.
Exner, M. E., and R. F. Spalding. Ground-Water Contamination
and Well Construction in Southeast Nebraska. Ground Water
23:1. 1985.
Grahm, W. G., D. W. Clapp, and T. A. Putkey. Irrigation
Wastewater Disposal Well Studies, Snake Plain Acruifer.
EPA-600/3-77-071. U.S. Environmental Protection Agency,
Office of Research and Development, Washington, D.C. 1977
A-l
-------
Hall, J. K., N. L. Hartwig, and L. D. Hoffman. Application
Mode and Alternate Cropping Effects on Atrazine Losses from
a Hillside. Journal _o_f Environmental Quality 12:336-340,
1983.
Hall, J. K., N. L. Hartwig, and L. D. Hoffman. Cyanazine Losses
in Runoff from No-Tillage Corn in 'Living1 and Dead Mulches
vs. Unmulched, Conventional Tillage. Journal of
Environmental Quality 13:105-110. 1984.
Hallberg, G. R. Agricultural Chemicals and Ground Water
Quality in Iowa. Iowa State University, Cooperative
Extension Service, Ames, Iowa. 1985.
Hallberg, G. R., and B. E. Hoyer. Sinkholes, Hydrogeology, and
Ground-Water Quality in NortheastIowa. Open File Report
82-3:120. Iowa Geological Survey, Iowa City, Iowa. 1982.
Hallberg, G. R., J. L. Baker, and G. W. Randall.
Utility of Tile-Line Effluent Studies to Evaluate the
Impact of Agricultural Practices on Ground Water.
Proceedings of the Agricultural Impacts on Ground Water
Conference. National Water Well Association, Dublin,
Ohio. 1986.
Hallberg, G. R., R. D. Libra, E. A. Bettis III, and B, E.
Hoyer. Hydrogeologic and Water Quality Investigations in
the Big Spring Basin, Clayton County, Iowa. Open File
Report 84-4. Iowa Geological Survey, Iowa City, Iowa.
1984.
Hanthorn, M. and M. Duffy. Corn and Soybean Pest Management
Practices for Alternative Tillage Systems. Inputs Outlook
and Situation: 14-23. Economics Research Service, U.S.
Department of Agriculture, Washington, D.C. 1983.
Helling, C. S. Agricultural Pesticides and Groundwater
Quality. Proceedings of the Agricultural Impacts _on
Groundwater Conference. National Water Well Association,
Dublin, Ohio. 1986.
Hinkle, M. K. Problems with Conservation Tillage.
Journal of Soil and Water Conservation 38:201-206.
Soil Conservation Society of America, Ankeny, Iowa. 1983.
A-2
-------
Johnson, J. S. The Role of Conservation Practices as BMPs.
Best Management Practices for Agriculture and Silviculture:
69-78. Ann Arbor Science Publications, Inc., Ann Arbor,
Michigan. 1979.
Knisel, W. G. CREAMS: A Field-Scale Model for Chemicals,
Runoff, and Erosion from Agricultural Management Systems.
USDA Conservation Research Report No. 26. 1980.
Kogan, M. Plant Resistance in Pest Management. Introduction
tg_ Insect Pest Management. John Wiley and Sons.
New York, N.Y. 1982.
Lichtenstein, E. P., K. R. Schultz, and T. W. Fuhreman.
Effects of a Cover Crop Versus Soil Cultivation on the Fate
and Critical Distribution of Insecticide Residues in Soil 7
and 11 Years After Soil Treatment. Pesticides Monitoring
Journal 5:218-222 and 761-765. 1971.
Lindslay, R. K., Kohler, M. A., and J. L. H. Paulhus.
Hydrology for Engineers. McGraw Hill Book Company,
New York, N.Y. 1975.
Logan, T.J., J.M. Davidson, J.L. Baker and M.R. Overcash,
Effects of Conservation Tillage on Ground-Water
Quality-Nitrate and Pesticides. Lewis Publishers, Chelsea,
Michagan. 1988.
Luckman, W. H. Insect Control in Corn-Practices and Prospects,
Pest Control Strategies, Smith E. H. and D. Pimental,
Eds. pp. 137-155. Academic Press, New York, N.Y. 1978.
Maas, R. P., S. A. Dressing, J. M. Kreglow, F. A. Koehler, and
F, J. Humenik, Best Management Practices for Agricultural
Non-Point Source Control Sediment, III: 49-51. North
Carolina Agricultural Extension Service. Biological and
Agricultural Engineering Department, North Carolina State
University, Raleigh, North Carolina. 1982.
Maas, R. P., S. A. Dressing, J. Spooner, M. D. Smolen,
and F. J. Humenik. Best Management Practices for
Agricultural Non-point Source Control Pesticides,
IV: 29-34. Biological and Agricultural "Engineering
Department, North Carolina State University, Raleigh, North
Carolina. 1984.
A-3
-------
Martin, J. F. and W. H. Leonard. Principles of Field Crop
Production. The MacMillen Compan., London, England. 1967.
National Science Foundation. Integrated Pest Management;
The Principles, Strategies, and Tactics of Pest Population
Regulation and Control in Major Crop Ecosystems. Progress
Report. Volume 1. 1975.
Nebraska, State of. Legislative Bill 284. 1986.
Nebraska, University of. farm, Ranch, and Home Quarterly.
30: No. 3. Special Edition 1984. Institute of
Agriculture and Natural Resources. 1984.
Newson, L. D. Progress in Integrated Pest Management of
Soybean Pests. Pest Control Strategies, F. H. Smith and D.
Pimentel, eds. pp. 157-180. Academic Press, New York,
N.Y. 1978.
Quinlan, J. F. , and R. D. Ewers. Ground Water Flow in
Limestone Terrains: Strategy Rationale and Procedure for
Reliable, Efficient Monitoring of Ground Water Quality in
Karst Areas. Proceedings of the Fifth National Symposium
and Exposition on Aquifer Restoration and Ground Water
Monitoring. National Water Well Association. Dublin,
Ohio. 1985.
Roberts, H. A. Weed Control Handbook and Principles.
Seventh Edition. Blackwell Scientific Publications.
Boston, Massachusetts. 1982.
Rudd, W. G., Revsink, W. G., Newson, L. D., Herzog, D. C.,
Jensen, R. L. and N. F. Marsolan. Tne Systems Approach to
Research and Decision Making for Soybean Pest Control.
New Technology of Pest Control. C. B. Huffker, ed.
pp. 99-122. John Wiley and Sons. New York, N.Y. 1980.
Schepers, J.S. and D.R. Hay,. Impacts of Chemigation on
Groundwater Contamination. Rural Groundwater
Contamination. Frank M. D'Irti and Lois G. Wolfson, eds.
Lewis Publishers, Inc. Chelsea, Michigan. 1987.
Smith, E. E., Lang, E. A., Casler, G. L., and R. W. Hexem.
Cost-Effectiveness of Soil and Water Conservation Practices
for Improvement of Water Quality. Effectiveness of Soil
and Water Conservation Practices for Pollution Control.
U.S. Environmental Protection Agency, Office of Research
and Development, Athens, Georgia. 1979.
A-4
-------
Stryk, Y., et. al. Atrazine Residues in Tile Drain Water as
Affected by Cropping Practices and Fertility Levels.
Canadian Journal of Soil Science 57:249-259. 1977.
U.S. Department of Agriculture. Cooperative Extension
and Agricultural Profitability—Integrated Pest Management
Reduces Costs and Increases Income. U.S. Dept. of
Agriculture, Cooperative Extension Service. Washington,
D.C. April 1985.
U.S. Department of Agriculture. Irrigation. Engineering
Field Manual. Soil Conservation Service. U.S. Department
of Agriculture. Washington, D.C. 1983.
U.S. Environmental Protection Agency. Effectiveness of Soil
and Water Conservation Practices for Pollution Control.
U.S. Environmental Protection Agency, Office of Research
and Development. Athens, Georgia. 1979.
U.S. Environmental Protection Agency. Pesticides in Ground
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D.C. 1986.
van der Bosch, R. The Pesticide Conspiracy. Doubleday Company,
Inc., Garden City, New York 1978.
van de Leeden, Frits, and F. L. Troise. Climates of the
States. Water Information Center, Inc., Port Washington,
New York. 1974.
Wisconsin, University of. Agriculture Management Practices to
Minimize Groundwater Contamination. Environmental
Resources Center. Madison, Wisconsin. 1987.
A-5
-------
APPENDIX B
DEGRADATION RATE CONSTANTS FOR SELECTED PESTICIDES
Tables B-l and B-2 present degradation rate constants for
selected pesticides on foilage and for selected pesticides in
soil respectively. These constants express the rates at which
pesticides decay or breakdown when present on plant surfaces or
in the soil. Knowledge of these degradation rates can aid in
preventing ground-water contamination. Pesticides which
degrade relatively fast should be chosen over those which
degrade slower, assuming that performance and applicability are
consistent with intended use.
B-l
-------
TABLE B-l: DEGRADATION RATE CONSTANTS FOR SELECTED
PESTICIDES ON FOLIAGE
Class
Group
Decay Rate
(days'1)
Organochlorine
CO
I
M
Oiyanophosphate
Carbamate
Fast
(aldrin, dieldrin, ethylan, heptachlor, lindane
methoxychlor).
Slow
(chlordane, DDT, endrin, toxaphene).
Fast
(acephate, chlorpyrifos-methyl, cyanophenphos,
diazinon, dipterex, ethion, fenitrothion, leptophos,
malathion, methidathion, methyl parathion, phorate,
phosdrin, phosphamidon, quinalphos, alithion,
tukutliion, triazophos, trithion).
SJow
(azinphosmethyl, demeton, dimethoate, EPN, phosalone).
Fast
(carbofuran)
Slow
(carbaryl)
0.231 - 0.1386
0.1195 - 0.0510
0.2772 - 0.3013
0.1925 - 0.0541
0.630
0.1260 - 0.0855
-------
ro
i
Class
TABLE B-l: DEGRADATION RATE CONSTANTS FOR SELECTED
PESTICIDES ON FOLIAGE
(Continued)
Group
Decay Rate
(days~l)
Pyrethroid
Pyridine
Benzole acid
(permethrin)
(pichloram)
(dicamba)
0.0196
0.0866
0.0745
Source: Knisel, 1980.
-------
TABLE B-2:
SOIL DEGRADATION RATE CONSTANTS FOR
SELECTED PESTICIDES
Chemical Name
Alachlor
Aldicarb
Atrazine
Benanyl
Bifenox
Carbaryl
Carbofuran
Chlordane
Chloropropham
Cyanazine
Dalapon
Diazinon
Dicamba
Dichlobenil
2,4-Dichlorophenoxy-
acetic Acid
Dinoseb
Diuron
Fenitrothion
Fluometuron
Linuron
Malathion
Methoxychlor
Methyl Parathion
Monuron
Parathion
Permethrin
Phorate
Picloram
Propachlor
Propanil
Propazine
Simazine
Toxaphene
Trifluralin
Zineb
Degradation Rate
Constant (days"1)
0. 0384
0.0322
0.0149
0 . 1486
0 . 1420
0. 1196
0.0768
0. 0020
0 . 0058
0.0495
0.0462
0.0330
0.2140
0.0116
0.0693
0.0462
0.0035
0.1155
0.0231
0 .0280
0 .291
0.0046
0.2207
0 . 0046
0.2961
0.0396
0.0363
0.0354
0 .0231
0.693
0.0035
0 . 0539
0 . 0046
0 . 0956
0.0512
- 0. 0116
- 0.0063
- 0.0023
- 0.0768
- 0.0079
- 0.0007
- 0.00267
- 0.0231
- 0.0067
- 0.0197
- 0.0039
- 0 .0231
- 0.0231
- 0.0014
- 0.0578
- 0. 0039
- 0.4152
- 0.0033
- 0. 0020
- 0.0046
- 0. 0040
- 0. 0019
- 0. 0139
- 0.231
- 0.0017
- 0.074
- 0.0026
Reference
a
a
a
a
a
a
a
d
c
d
a
a
d
d
d
a
c
a
a
a
a
d
a
e
a
a
d
d
d
a
e
a
a
B-4
-------
TABLE B-2: SOIL DEGRADATION RATE CONSTANTS FOR
SELECTED PESTICIDES
(Continued)
Nash, R.G., 1980. Dissipation Rate of Pesticides from
Soils. Chapter 17. IN CREAMS: A Field Scale Model for
Chemicals Runoff, and Erosion from Agricultural Management
Systems. W. G. Knisel, ed. USDA Conservation Research
Report No. 26. 643 pp.
Smith, C.N., Partition Coefficients (Log Kow) for
Selected Chemicals. Athens Environmental Research
Laboratory, Athens, GA. Unpublished report, 1981.
Herbicide Handbook of the Weed Science Society of America,
4th ed. 1979.
Control of Water Pollution from Cropland, Vol. I, a manual
for guideline development, EPA-600/2-75-026a.
Smith, C.N. and R. F. Carsel. Foliar Washoff of Pesticides
(FWOP) Model: Development and Evaluation. Accepted for
publishing in Journal of Environmental Science and
Health - Part B. Pesticides, Food Contaminants, and
Agricultural Wastes, B 19(3), 1984.
Source: Carsel, et al. 1984
B-5
-------
APPENDIX C
DOMINANT SOIL ORDERS OF THE U.S.
Figure C-l shows patterns of dominant soil orders and
suborders of the U.S. and identifies crops and topographic
conditions that are associated with each. This figure provides
information useful in the identification of topographic and
soil conditions which is necessary for the selection of
mitigation measures to reduce pesticide leaching. How these
factors should be considered in the selection of mitigation
measures is described in Part I of this report.
C-l
-------
o
I
FIGURE C-1
PATTERNS OF SOIL ORDERS AND SUBORDERS OF THE U.S.
SOURCE U S Soil Coci'.prvalion Srvu-p
-------
U S DEPARTMENT OF AGRICULTURE
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PATTERNS OF SOIL ORDERS AND SUBORDERS OF THE U.S.
C-3
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APPENDIX D
INFORMATION SOURCES
To design an appropriate State or Local program to reduce
risks of pesticide contamination, consideration must be given
to hydrological conditions, cropping patterns, agricultural
practices, pest control needs, and alternatives. Information
on these topics is available from a variety of sources; the
guide which follows describes several sources including Key
agencies and organizations and the information they can provide
(see Figure D-l for a summary).
The Cooperative Extension Service (CES), a joint program of
the U.S. Department of Agriculture (USDA), States, and
counties, serves the American agricultural community tnrough
dissemination and application of information generated by
research efforts. The CES is the most extensive and readily
available source of information on agriculture and plays an
important role in educating pesticide users. Local offices of
the CES may be found in the telephone directory, usually listed
under the U.S. Department of Agriculture.
The U.S. Soil Conservation Service (SCS), among other
activities, provides direct technical assistance to landowners
in designing and carrying out plans for conserving soil and
protecting water quality. SCS soil surveys provide detailed
information on soil type and distribution as well as other data
useful in assessing the potential for ground water
contamination from pesticides. Local offices of the SCS may
also be found in the telephone directory, usually under
U.S. Department of Agriculture.
Land Grant Universities generally nave major agriculture
and science programs and represent excellent sources of
information. Federal and State governments and industry
sponsor many projects conducted by leading researchers at these
institutions. Firsthand knowledge of local or regional
agricultural practices may be obtained through contact with
these investigators. Land Grant Universities are also linked
to the Cooperative Extension Service.
Agricultural Experiment Stations and Water Resources
Research Institutes are sources of local and regional
information and are usually associated with major universities
D-l
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or colleges. Results of research typically are available as
technical reports documenting findings and observations of
agricultural and water resource investigations.
States generally have a Department of Natural Resources,
Water Quality, Environmental Protection, or similarly named
agency responsible for managing and protecting ground water.
These agencies are potential sources of information, as are
State Soil and Water Conservation Agencies. Offices of State
agencies can be found in the telephone directory. State
Geological Surveys generally have major ground water programs,
and in light of the recent interest in pesticide contamination,
many may have ongoing research projects in this area. State
surveys are sometimes located in capital cities out may also be
associated with colleges or universities.
Tne U.S. Geological Survey (USGS) is the principal Federal
agency conducting ground water resources investigations.
Technical details concerning the geology and water resources of
many areas of the country are presented in USGS Water Supply
Papers. These reports, usually available at major college or
university libraries, provide information essential for
evaluating the vulnerability of the study area to ground water
contamination. The USGS headquarters is located in Reston,
Virginia, with numerous offices in other locations.
U.S. Geological Survey
12201 Sunrise Valley Drive
Reston, Virginia 22091
(703)860-7000
The Conservation Technology Information Center is a
clearinghouse for information encouraging conservation systems
for soil and water on croplands. Information relating to
conservation tillage and water quality protection is currently
available; fact sheets on pesticide and nitrate contamination
of ground water are under development at the time of this
writing. For specific information, contact:
The Conservation Technology Information Center
1220 Potter Drive
Room 170
Purdue Research Park
West Lafayette, Indiana 47906-13314
(317)494-9555
D-2
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The National Agriculture Library publishes a series of
commodity-oriented environmental bibliographies. Two recent
bibliographies -- "Conservation Tillage and "Chemigation" --
include the latest available information from United States
publications involving commodity protection relating to these
two aspects of ground water contamination, pesticides use, and
alternative agricultural practices. These, and other
publications, can be obtained through:
National Agricultural Library
U.S. Department of Agriculture
Beltsville, Maryland 20705
Resources For The Future, a non-profit research
association, has compiled a data base of pesticide use
estimates for a typical year in the 1980s. It details tne
percent of acreage treated with pesticides and the application
rate per acre on a State and county level. Information
concerning this data base can be obtained from:
Resources For the Future
1616 P. Street, N.W.
Washington, D.C. 20036
(202)328-5000
National Pesticide Information Retrieval System (NPIRS) is
a data base produced by Purdue University. It contains
pesticide chemical and registration data for 50,000 products
registered by EPA, as well as thousands of State
registrations. Facts sheets for each registered pesticide
contain data on product names, pesticide use patterns, EPA
registration numbers, formulations, active ingredients, and
sites and crops where the pesticides are used. Information on
NPIRS, including accessing information, can be obtained oy
contacting:
User Services Manager, NPIRS
Entomology Hall
Purdue University
West Lafayette, Indiana 47907
(317) 494-6614
The Institute for Alternative Agriculture is an
organization dedicated to advancing agricultural economics,
resource conservation, and environmental protection.
Information on alternative farming practices which may be
implemented to reduce the potential for ground water
contamination from pesticides is available from the Institute:
D-3
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Institute for Alternative Agriculture
9200 Edmonston Road
Suite 117
Greenbelt, Maryland 2U770
(301)441-8777
Farm Chemicals Handbook, published annually, is a directory
and reference for fertilizer and pesticide users. It contains
information on specific pesticides, including cnemical names,
trade names, common names, chemical properties, toxicity,
applications, and formulation. The handbook can be obtained by
contacting:
Meister Publishing Company
37841 Euclid Avenue
Willoughby, Ohio 44094
(216) 942-2000
The Weed Science Society of America produces the "Heroicide
Handbook.1 It contains an alphabetical listing of all
available herbicides and includes information on common names;
chemical names; chemical and physical properties, including
structural and molecular formulae, vapor pressure, and
adsorption parameters; herbicide use, including application
methods, associated crops, and application rates; toxicology;
and behavior in soil and general potential for leaching. This
publication can be obtained by contacting:
Weed Science Society of America
309 West Clark Street
Campaign, Illinois 61820
(217) 356-3182
Weed Control Manual and Insect Product Guide contain
listings of insecticides and herbicides by various crop types.
Also included are mixing instructions, use instructions, and
lists of weeds and insects controlled by each pesticide. The
guides can be obtained by contacting:
Ag Consultant and Fieldman
37841 Euclid Avenue
Willoughby, Ohio 44094
(216) 942-2000
D-4
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TABLE D-1
SOURCES OF INFORMATION
SOURCES
TYPES OF INFORMATION
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COOPERATIVE EXTENSION SERVICE
SOIL CONSERVATION SERVICE
LAND GRANT UNIVERSITY
STATE AGRICULTURAL EXPERIMENT STATION
STATE WATER RESOURCES RESEARCH INSTITUTE
STATE GEOLOGICAL SURVEY
STATE GROUND WATER AGENCY
STATE SOIL AND WATER CONSERVATION AGENCY
U.S. GEOLOGICAL SURVEY
CONSERVATION TECHNOLOGY INFORMATION CENTER
NATIONAL AGRICULTURAL LIBRARY
RESOURCES FOR THE FUTURE
NATIONAL PESTICIDE INFORMATION RETRIEVAL SYSTEM
INSTITUTE FOR ALTERNATIVE AGRICULTURE
FARM CHEMICALS HANDBOOK
HERBICIDE HANDBOOK
INSECT PRODUCT GUIDE
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