ES-NWQEP-84/02
xvEPA
United States Office of Research and
Environmental Protection Development
Agency Washington DC 20460
Best Management
Practices for
Agricultural Nonpoint
Source Control
IV. Pesticides
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BEST MANAGEMENT PRACTICES FOR AGRICULTURAL
NONPOINT SOURCE CONTROL
IV. PESTICIDES
for the project
RURAL NONPOINT SOURCE CONTROL WATER QUALITY
EVALUATION AND TECHNICAL ASSISTANCE
(NATIONAL WATER QUALITY EVALUATION PROJECT)
USDA COOPERATIVE AGREEMENT 12-05-300-472
EPA INTERAGENCY AGREEMENT AD-I2-F-0-037-0
PROJECT PERSONNEL
RICHARD P. MAAS
STEVEN A. DRESSING
JEAN SPOONER
MICHAEL D. SMOLEN
FRANK J. HUMENIK
EXTENSION SPECIALIST
EXTENSION SPECIALIST
EXTENSION SPECIALIST
PRINCIPAL INVESTIGATOR
PROJECT DIRECTOR
BIOLOGICAL 8 AGRICULTURAL ENGINEERING DEPT.
NORTH CAROLINA STATE UNIVERSITY
RALEIGH , NORTH CAROLINA 27650
EPA PROJECT OFFICER
JAMES W. MEEK
IMPLEMENTATION BRANCH
WATER PLANNING DIVISION
WASHINGTON.D.C.
USDA PROJECT OFFICER
FRED N. SWADER
EXTENSION SERVICE
ENVIRONMENTAL QUALITY
WASHINGTON, D.C.
SEPTEMBER ,1984
Printed on Recycled Paper
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ACKNOWLEDGEMENTS
This report is a product of the joint USDA-EPA project,
"Rural Nonpoint Source Control Water Quality Evaluation and
Technical Assistance" more commonly known as the National
Water Quality Evaluation Project (NWQEP). The authors wish
to thank the members of the USDA-EPA Project Advisory Com-
mittee timely and constructive review of the manuscript.
We extend special thanks to Ms. DeAnne Johnson for her
considerable assistance in assembling the published litera-
ture used as the basis of this report.
Much credit is also due to Ms. Sharon Springs and Mrs.
Naomi Muhammad for typing and proofing preliminary and final
drafts of this report.
This work was funded cooperatively by USDA and U.S.EPA as
part of the Rural Nonpoint Source Control Water Quality
Evaluation and Technical Assistance project under USDA Coop-
eration Agreement 12-05-300-472 and EPA Interaqencv
Agreement AD-12-F-0-037-0.
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EXECUTIVE SUMMARY
Since about the 1950's pesticide contamination of water
resources has become recognized as a serious, pervasive yet
largely unquantifiable problem of major ecological and pub-
lic health concern. Although numerous case examples of
water resource impairments have been reported, the present
scope of the problem remains unclear due to 1) the intermit-
tant and transient nature of pesticide inputs, 2) the often
subtle ecological and human health effects of low level con-
tamination, 3) rapid changes in pesticide types and usage
patterns and 4) the extremely high expense of monitoring
pesticide levels in aquatic systems. In spite of problem
definition difficulties a few facts give some perspective to
the dynamics of the problem:
1. Pesticides have been the leading single documented
cause of fishkills in the U.S. over the past 20
years.
2. Evidence continues to accumulate on the acute, chron-
ic and mutagenic human health effects of a growing
number of pesticides at the part-per million and
part-per billion levels commonly encountered in both
ground and surface water.
3. Herbicide concentrations appear to be generally in-
creasing in groundwaters in the U.S. concomitant with
increased herbicide usage.
4.
5.
Aquatic biota, sediments, and agricultural soils con-
tinue to exhibit levels of banned organochlorine
residues which are only moderately lower than ten
years ago.
Estimates are that somewhere between 0.5% and 3% of
the approximately 700 million pounds of pesticides
used in the U.S. reach ground or surface water prior
to degradation.
Appropriate strategies to minimize water quality impacts
of pesticides are highly dependent on pesticide use trends.
Overall insecticide use on major crops dropped by 46% be-
tween 1976 and 1982. The majority of the decrease is
attributable to a 74% decrease in cotton applications
brought about by IPM programs, application efficiency im-
provements and substitution with synthetic pyrethroids. Use
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of the persistent, highly toxic, and bioaccumulated
pesticide, toxaphene, decreased 81% during this same period.
In contrast, herbicide usage continued to increase especial-
ly in corn (15%) and soybean (35%) production systems.
Conceptually, there are three basic types of management
options for reducing the water pollution potential of pesti-
cide usage:
1. Reduce the amount of pesticide applied by:
a) improving application efficiency
b) using non-chemical (IPM) control measures
2. Substitute less toxic, less persistent or less mobile
pesticides
3. Reduce or retard the transport of applied pesticides
from fields to aquatic systems.
The most effective mix of management options is highly
dependent on dominant transport modes for a particular pes-
ticide class. The primary modes of transport to aquatic
systems include: l)direct application, 2)with surface or
subsurface runoff, either dissolved, granular or adsorbed on
sediment particles, 3)aerial drift, 4)volatilization and
subsequent atmospheric deposition, 5)uptake by biota and
subsequent movement in the food web.
The relative importance of these transport routes is in-
fluenced by many factors including the physical/chemical
properties of the pesticide, the method and timing of appli-
cation, weather and climate conditions and land
characteristics (soil properties, slopes, crops). The major
transport routes of the pesticide classes considered in this
report can be summarized as follows:
1. Organochlorines (toxaphene).
Volatilization - 20-90% depending on weather condi-
tions. Drift - > 50% if aerially applied. Surface
runoff - usually < 1% almost entirely in adsorbed
phase. Biotic uptake small but highly significant
for aquatic ecosystems.
2. Carbamates (carbaryl, carbofuran). These are lost
from fields almost entirely in the dissolved phase of
runoff. Some leaching through soil profiles is su-
spected but largely undocumented.
3. Organophosphorius insecticides - (methylparathion).
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Volatilization - 20-90% depending on weather
conditions. Drift - > 50% if aerially applied. Sur-
face runoff losses occur in both dissolved and
adsorbed phases with the relative magnitude dependent
on the particular insecticide and soil type.
4. Triazine herbicides (atrazine, cyanazine).
Volatilization - little information available. One
study measured 40% from warm (35 C) soils. Drift -
0-40% depending on application method. Surface run-
off - 0.2 to 16% depending on interval between
application and first runoff event. Most loss is in
dissolved phase. Leaching potential is significant.
Numerous studies have detected triazines in qroundwa-
ter.
5. Anilide herbicides (alachlor, propachlor).
Volatilization and Drift - No information. Surface
runoff losses - 1.0 to 8.6% almost entirely in dis-
solved phase.
6. Bipyridylium herbicides (paraquat).
Volatilization - negligible. Drift - small but envi-
ronmentally significant. Runoff losses - entirely in
adsorbed phase - not generally biologically avail-
able.
The water quality effectiveness of various classes of
pesticide Best Management Practices are summarized below:
1. Application efficiency improvement. (restricting
aerial spraying, using larger drop sizes, restricting
application when runoff events are predicted, apply-
ing only on windless days, evening or night
spraying). These BMPs reduce pesticide transport by
all routes but are particularly effective in reducing
drift and volatilization losses.
2. Integrated Pest Management (IPM). These pest control
systems significantly reduce the amounts of pesticide
needed . A linear relationship between application
rates and field loss is assumed. This assumption may
err in either direction but is generally accepted.
IPM systems reduce pesticide inputs to aquatic sys-
tems by all routes.
3. Soil and Water Conservation Practices (SWCPs). These
practices affect runoff and soil leaching transport
modes. For pesticides that are lost primarily in the
sediment adsorbed phase, field loss reductions will
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be somewhat less than erosion reductions because of
pesticide enrichment on the more easily eroded fine
sediment fraction. For pesticides lost primarily in
the dissolved phase, loss reductions will be approxi-
mately equal to reductions in runoff volume. Some
tradeoff is inevitable, however, between reducing
surface losses and increasing soil leaching poten-
tial.
Conservation tillage systems are a special case as
far as their effects on pesticide runoff losses. If
the first rainfall event after application is rela-
tively small, these systems exhibit dramatic
reductions in pesticide losses relative to conven-
tional tillage because little or no runoff is
produced and the pesticide has an opportunity to be
washed off the surface residue and into the soil.
However, if the first post-application event is
large, loss from these systems is greater than from
conventional tillage because the pesticide intercept-
ed by the surface residue is highly susceptable to
transport.
4. Substitution of less toxic, less persistent or more
selective pesticides.
The most obvious examples of this BMP are the re-
striction or elimination of persistent organpchlorine
insecticides, which continues to have a positive ef-
fect on aquatic ecosystems, and the substitution of
synthetic pyrethroids. The synthetic pyrethroids are
more selective, which enhances natural population
control mechanisms, and they are applied at lower
rates than the chemicals they replace. However,
while field studies are lacking, laboratory studies
show synthetic pyrethroids to be extremely toxic to
many aquatic organisms.
The pesticide imput reductions to aquatic systems
which can be accomplished using current BMP technolo-
gy are summarized below for major U.S. crops.
Corn: Insecticide application can be reduced by
40-70% by greater use of crop rotations and
field monitoring of insect populations. Sur-
face runoff losses can be decreased by about
40% by SWCPs.
Soybeans: Soybean production has recently moved into
new geographic areas where heavy insect and
weed problems exist. The challange will be to
prevent a proliferation of pest problems from
indiscrete pesticide use. In the southeast and
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south-central U.S. pesticide usage can be kept
at about its current level using IPM and im-
proved application techniques. Losses to
aquatic systems can be reduced about 40% using
SWCPs.
Cotton: Insecticide use has decreased by 74% since
1976 as a result of IPM programs and the use of
synthetic pyrethroids. Further, but less dra-
matic, reductions are possible. The use of
toxaphene can and should be eliminated from
cotton production. Reductions in herbicide us-
age of 30-40% should be possible using crop
rotations, resistant varieties and more effi-
cient (non-aerial) application techniques.
Relative to potential use reductions and chang-
es, SWCPs will have little effect (10-20%) on
pesticide losses from cotton acreage.
Deciduous Tree Fruits: Reductions in pesticide use
of 50-80% can be accomplished using currently
available IPM technology.
Tobacco: Tobacco represents a small but intense
source of pesticides to aquatic systems in the
Southeast. Because of the inherent need for
direct field drainage the delivery ratio of ap-
plied pesticides to aquatic systems is very
high. The most effective improvements will
come through IPM systems which can currently
reduce pesticide use by about 30 to 60%.
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CONTENTS
ACKNOWLEDGEMENTS iii
EXECUTIVE SUMMARY V
Chapter
1. INTRODUCTION 1
Background 1
Pesticide Usage 3
Occurrence and Effects of Pesticides in
Aquatic Systems 11
Occurrence 11
Ambient Studies 11
Directed Studies 12
Effects of Pesticides on Aquatic Systems ... 12
Toxicity Studies 12
Effects on Water Quality 13
2. MODES OF PESTICIDE TRANSPORT 15
Selection of Major and Representative
Pesticides .15
Transport to Aquatic Systems 16
Organochlorine Insecticides 16
Volatilization and Drift 17
Runoff and Soil Leaching 17
Biotic Transport Modes 18
Organophosphorus (OP) Insecticides 18
Aerial Drift and Volatilization 19
Runoff and Soil Leaching 19
Leaching to Groundwater 20
Carbamate Insecticides 20
Runoff and Soil Leaching 21
Drift and Volatilization 21
Triazine Herbicides 22
Runoff and Soil Leaching 22
Drift and Volatilization 24
Anilide Herbicides: Alachlor, Propachlor ... 27
Bipyridylium Herbicides: Paraquat 27
3. BEST MANAGEMENT PRACTICES FOR REDUCING PESTICIDE
DELIVERY TO AQUATIC SYSTEMS 29
SWCPs 29
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Non-structural Practices 29
Conservation tillage 29
Contouring 31
Stripcropping 32
Grassed Waterways 32
Cover crops . 32
Filter Strips 33
Structural Practices 33
Terraces 33
Sediment Basins 34
Summary of Effect of SWCPs on Pesticide
Inputs to Aquatic Systems 34
Pesticide Formulations and Application Methods . . 36
Formulations 36
Application Methods 37
Aerial Application . . . 37
Ground Application 39
Management - Timing 40
Reducing'drift .losses 41
Reducing volatilization losses 41
Reducing runoff losses 41
4. INTEGRATED PEST MANAGEMENT (IPM) SYSTEMS 43
Basic Principles . 43
Monitoring 46
Control Action Thresholds 46
Biological Controls 47
Cultural Controls . 48
Evaluating IPM Programs 49
Substitution of More Selective or Less
Persistent Pesticides 50
5. PESTICIDE BMP SYSTEMS BY CROP AND REGION 53
Pesticide BMPs for Corn 54
Insecticide Reduction through IPM 54
Scouting 54
Crop Rotation 55
Possible Herbicide Reductions through IPM ... 56
Pesticide BMPs for Soybeans 58
Possible Reduction in Insecticide Use
Through IPM 59
Possible Reduction in Herbicide Use 60
Pesticide BMPs for Cotton 60
Potential Insecticide Reductions Through
IPM 63
Potential Herbicide Reductions . 64
Tobacco 64
Deciduous Tree fruits 65
Other Crops with High Pesticide Usage 65
Summary of Pesticide BMPs for Major Crops .... 66
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6. CONCLOSIONS 69
REFERENCES CITED 73
Table
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
LIST OF TABLES
page
Farm Herbicide Use by Crop, 1971, 1976, and 1982 . . 4
Farm Insecticide Use by Crop, 1971, 1976, and
1982 5
Total Farm Pesticide Use, 1971, 1976, and 1982 ... 7
Corn Pesticide Use, 1976 and 1982 8
Soybean pesticide use, 1976 and 1982's 9
Cotton Pesticide Use, 1976 and 1982 10
Atrazine Runoff Losses Summary 25
Per-Acre Herbicide Cost for Corn and Soybean
Production By Tillage System 31
Effects of Soil and Water Conservation Practices . . 36
Options for Reducing Pesticide Application
Losses
38
Major Components of Integrated Systems for
Reducing Pesticide Usage 44
Estimates of Potential Reductions in Field
Losses of Pesticides for Corn Compared to a
Conventionally and/or Traditionally Cropped
Field (1) 57
13. Estimates of Potential Reductions in Field
Losses of Pesticides for Cotton Compared to a
Conventionally and/or Traditionally Cropped
Field (1) 62
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Chapter 1
INTRODUCTION
1.1
BACKGROUND
The agronomic importance of pest control, coupled with
the increasing concern about the adverse side-effects of
pesticides on public health and the environment, present a
challenge to the agricultural community to develop pest con-
trol strategies which are more economical, effective over
the long term, and less harmful to public health and the en-
vironment. The present report is intended to consider the
tools available to address this challenge putting special
emphasis on water quality considerations.
Shortly after World War II pest control shifted largely
from a biological/ecological discipline to a chemical one.
This era of dependence on pesticides (particularly insecti-
cides) has provided good disease control, spectacular insect
control, and more recently, adequate weed control (1). Dur-
ing the 1970's, however, a myriad of adverse effects
resulting from over use or improper use of chemical pest
control began to surface including:
1. The decimation of various predator bird populations
as persistent organochlorine pesticides moved through
the food chain (2);
2. The appearance of pesticide contamination in surface
water, groundwater and aquatic ecosystems on a global
scale;
3. The implication of a large number of pesticides as
potent carcinogens (110);
4. The contamination of agricultural soils;
5. The massive destruction of non-targeted organisms re-
sulting in the loss of natural pest population
controls and the elevation of nonpest species to pest
status (3);
6. The rapid evolution of resistant pest strains;
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7. The neglect and consequent loss of crop varieties
with natural resistance to pests.
Two outcomes of these adverse effects are that: (1) pes-
ticides have been identified as the single leading cause of
fishkills in U.S. surface waters, with 18% of reported inci-
dents attributed to use of these chemicals (5): and (2)
although the amount of pesticides used today is at least
several times greater than in 1961, twice .as large a share
of U.S. crops are lost to pests (6). These statistics
clearly point out the need for continued development of new
pesticide management strategies to control pests effectively
over the long term and to reduce adverse environmental im-
pacts.
The term, pesticide, in this report is defined as any
chemical or biochemical agent used to reduce organism-caused
damage to crops, livestock or forests, including insecti-
cides, herbicides, fungicides, nematocides and rodenticides.
The purpose of this report is to describe..the factors and
available research results relevant to selecting the most
appropriate pesticide Best Management Practices (BMPs) and
BMP systems. The intent is to optimize agricultural produc-
tion while minimizing the water quality impact. tfo the
extent possible the selection of pesticide BMPs is consid-
ered on a regional basis emphasizing the predominant crops
and pesticides of each region. The review of the literature
on each subtopic is not intended to be exhaustive due to the
volume of literature available in the pesticide and pest
management field. In addition, much of the literature in
this area is in the form of University reports, state Exten-
sion Service Bulletins, and other non-reviewed publications
of limited distribution. However, an attempt has been made
to consider all refereed articles and reviews for each topic
in the synthesis of the discussions and conclusions. The
Southern Water Resources Information Service (SWRSIC) and
AGRICOLA were the primary computer data bases surveyed as
well as many other miscellaneous sources especially the Na-
tional Water Quality Evaluation Project (NWQEP) Library
System (144). The spatial placement of BMPs within a water-
shed to obtain maximum water quality benefits is not
addressed in this report. This concept commonly referred to
as targeting to critical areas, is fully addressed in an-
other 'recent NWQEP publication (159).
Conceptually there are three basic options for reducing
the water pollution potential of pesticide usage:
1. Reducing the amount of pesticide applied by:
a) Improving application efficiency.
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b) Using non-chemical control measures;
2. Substituting less toxic, less persistent or less mo-
bile pesticides;
3. Reducing the transport of applied pesticides from
fields to aquatic systems.
The BMPs available under Option # 1 generally include more
efficient application methods in addition to a large array
of biological management methods which in conjunction with
traditional pesticides form what is known as Integrated Pest
Management (IPM). Option # 2 generally involves the devel-
opment of more selective and less persistent agents often
termed 3rd or 4th generation pesticides. BMPs available un-
der Option # 3 include improved application methods as well
as a large variety of well-known soil and water conservation
practices (SWCPs) which are designed to reduce sediment and
runoff losses.
The transport of pesticides from application sites to
aquatic systems is not fully understood; however, the prima-
ry modes appear to be direct dumping or spills, transport in
overland runoff, transport in interflow (both to ground and
surface waters), atmospheric drift into surface waters, dep-
osition of air-borne soil particles with attached
pesticides, and evaporation of pesticides from foliage or
soil followed by subsequent redeposition (7). The relative
importance of each of these transport mechanisms will depend
on many factors including the physical/chemical properties
of the pesticide, method of application, land characteris-
tics, and climate. These factors will be discussed in depth
in Section II on pesticide transport. SWCPs will generally
affect only the fraction of pesticide lost in runoff (solid
phase, adsorbed and dissolved) whereas pest control tech-
niques which reduce the amount of pesticide applied will
generally reduce .pesticide losses through all transport
routes (8).
1.2 PESTICIDE USAGE
In the context of optimizing pesticide management prac-
tices for water quality concerns it is important to
understand actual current pesticide usage patterns. The
pesticide usage data presented are taken from a USDA survey
through 1982 (63). Table 1 shows both the total amounts of
herbicides used by crop and the percentage of acres treated.
These data show that herbicide usage is still increasing,
and in fact, the total amount more than doubled in the
1971-1982 period. More significantly, the percentage of row
crop acreage treated with herbicides has increased from 71
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to 91 percent. Corn and soybeans account for 82 percent of
herbicide use.
TABLE 1
Farm Herbicide Use by Crop, 1971, 1976, and 1982
Crop
Row crops
Corn
Soybeans
Cotton
Grain sorghum
Peanuts
Tobacco
Total
Grain crops
Rice
Wheat
Other
Total
Forage crop
Alfalfa
Other hay
Pasture and range
Total
Total
Pounds of active
ingredient (a.i.)
1971 1976 1982
Proportion of
acres treated
1971 1976 1982
101.1
36.5
19.6
11.5
4.4
0.2
173.3
8.0
11.6
5.4
25.0
0.6
V
8.3
8.9
207.2
-Million-
207.1
81.1
18.3
15.7
3.4
1.2
326.8
8.5
21.9
5.5
35.9
1.6
I/
9.6
11.2
373.9
243.4
125.2
17.3
15.3
4.9
1.5
407.6
13.9
18.0
5.9
37.8
0.3
0.7
5.0
6.0
451.4
79
68
82
46
92
7
71
95
41
31
38
1
1
1
1
17
-Percent-
90
88
84
51
93
55
84
83
38
35
38
3
2
1
1
22
95
93
97
59
93
71
91
98
42
45
44
3 3
I/ Quantity of herbicides applied to other hay is
included in the alfalfa figure.
In Table 2 the same data are shown for insecticide use.
In contrast to the trend for herbicides, insecticide usage
has dropped dramatically since 1976. Most of this decrease
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is attributable to the increased use of more effective
synthetic pyrethroids (chemical analogs of natural insect
hormones), improved application efficiencies, and integrated
pest management. Corn and cotton receive the greatest share
of insecticides accounting for 66 percent of total usage.
TABLE 2
Farm Insecticide Use by Crop, 1971, 1976, and 1982
Crop
Row crops
Corn
Soybeans
Cotton
Grain sorghum
Peanuts
Tobacco
Total
Grain crops
Rice
Wheat
Other
Total
Forage crops
Alfalfa
Other hay
Pasture and range
Total
Total
Pounds of active
ingredient (a.i.)
1971 1976 1982
Proportion of
acres treated
1971 1976 1982
25.5
5.6
73.4
5.7
6.0
4.0
120.2
0.9
1.7
0.8
3.4
2.5
I/
0.2
2.7
126.3
-Million-
32.0
7.9
64.1
4.6
2.4
3.3
114.3
0.5
7.2
1.8
9.5
6.4
I/
0.1
6.5
130.3
30.1
10.9
16.9
2.5
1.0
3.5
64.9
0.6
2.4
0.2
3.2
2.5
0.1
*
2.6
70.7
35
8
61
39
87
77
31
35
7
3
6
8
**
0
**
-Percent-
38
7
60
27
55
76
29
11
14
5
12
13
2
**
1
37
12
36
26
48
85
26
16
3
1
3
7
* *
* *
* *
* = less tha 50,000 pounds (a.i).
** = less than 1 percent.
I/ Quantity of insecticides applied to other hay is included
the alfalfa figure.
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Table 3 summarizes the total amounts of various insecti-
cides and herbicides used in the U.S. for agricultural
purposes,, Although these figures do not precisely represent
relative usage because they are do not consider differences
in application rate, some interesting trends are still evi-
dent. Of the herbicides, alachlor, atrazine and butylate
are the most heavily used. Atrazine has decreased in recent
years while butylate has rapidly increased in importance.
Many herbicide formulations are a mixture of atrazine and
other herbicides. Usage of 2,4-D and propachlor on cropland
has decreased greatly. However, 2,4-D is still widely ap-
plied directly to surface waters for control of aquatic
macrophytes.
Carbofuran, methylparathion, and terbufos were the most
extensively applied insecticides in 1982. Toxaphene dropped
81 percent between 1976 and 1982 with concurrent increases
in synthetic pyrethroid usage. Organophosphorus class com-
pounds made up the majority of usage (55%). Other
pesticides, including dessicants, defoliants, fumigants,
growth regulators and miticides accounted for another 30.2
million pounds or 5.5 percent of pesticide usage.
In planning BMPs for pesticides, information on the ex-
tent of usage for each crop is needed. Corn, soybeans and
cotton account for approximately 82 percent of insecticide
usage and 85% percent of herbicide use. Table 4 shows pes-
ticides applied to corn in terms of acres treated and
amounts applied. 'Acres treated1 is probably a more accu-
rate measure of extent of use than amounts applied because
of differences in application rates. From Table 4 atrazine,
alachlor, butylate and cyanazine account for the majority of
herbicide used on corn. A wide variety of corn insecticides
are applied with terbufos, carbofuran and fonofos the most
predominant.
In Table 5 indicates that trifluralin ( a dinitroaniline),
metribuzen (a triazine), and alachlor (an anilide) are the
most common herbicides on soybeans. Insecticide use on soy-
beans is very limited (12 percent of planted acres). The
major types are methyl parathion, toxaphene, carbaryl and
synthetic pyrethroids.
Table 6, which summarizes pesticide use on cotton, indi-
cates that a wide variety of herbicides are used with
trifluralin, fluometuron (a urea herbicide) and MSMA (an ar-
senical) accounting for two-thirds of cotton acreage. The
most important insecticides include methyl parathion, syn-
thetic pyrethroids and toxaphene.
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TABLE 3
Total Farm Pesticide Use, 1971, 1976, and 1982
Pesticide
Herbicides
Alachlor
Atrazine
Bentazon 3/
Butylate+
Cyanazine 3/
EPTC+
Linuron
Metolachlor 3/
Propachlor
2,4-D
Trifluralin
All materials
Insecticides
Carbaryl
Carbofuran
Chlordimeform
Chlorpyrifos
DDT
EPN
Ethoprop
Fonofos
Methomyl
Methyl
parathion
parathion
Phorate
Synthetic
pyrethroids
Terbufos
Toxaphene
Dessicanta and
defoliants
Fumigants
Fungicides
Growth
regulators
Miticidea
Other
Total
Pounds
(a.i.)
14.0
53.9
5.6
3.4
1.7
22.3
30.5
10.3
207.2
11.2
2.8
-
*
13.5
0.9
0.6
0.6
0.3
27.1
7.0
3.6
-
31.9
17.4
9.1
6.4
5.0
1.1
32.5
405.0
Share
of
total
1971
6.8
26.0
2.7
1.6
0.8
10.8
14.7
5.0
68.4 I/
8.9
2.2
-
*
10.7
0.7
0.5
0.5
0.2
21.5
5.5
2.9
25.2
Pounds
(a.i.)
88.5
90.3
24.4
8.6
8.4
11.0
38.4
28.3
373.9
9.3
11.6
4.5
*
6.2
1.1
5.0
2.5
22.8
6.6
6.3
2.5
30.7
8.6
19.4
8.1
6.3
1.0
35.3
582.9
Share
of
total
1976
23.7
24.1
6.5
2.3
2.2
2.9
10.3
7.6
79.6
7.1
8.9
3.4
A
4.8
0.8
3.8
1.9
17.5
5.1
4.9
-
1.9
23.5
Pounds
of
(a.i.
84.6
76.0
9.9
54.9
16.6
8.3
6.4
37.0
7.8
23.3
36.1
485.3
2.3
7.3
0.7
5.1
1.4
2.2
5.2
1.7
10.7
4.2
4.0
2.6
8.7
5.9
9.4
7.9
6.6
6.0
0.3
__
552.3
Share
) total
1982
18.7
16.8
2.3
12.2
3.8
1.8
1.4
7.6
1.7
5.2
8.0
79.7
3.3
10.3
1.0
7.2
2.0
3.1
7.4
2.4
15.1
5.9
5.7
3.7
12.3
8.3
* none reported
* = less than 50,000 pounds (a.i.).
I/ Numbers in parentheses represent the shares of the
total pounds (a.i.) of the materials listed individually.
2/ Does not include tobacco plant bed applications.
3/ From Agrichemical Age 26(8):1982.
- 7 -
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TABLE 4
Corn Pesticide Use, 1976 and 1982
Pesticide
Acres treated (Million)
1976 1982
Founds (a.i.) (Million)
1976 1982
Herbicides
Alachlor
Atrazine
Butylate*
Cyanazine
Dicamba
EPTC+
Linuron
Metolachlor
Propachlor
Simazine
2,4-D
Other
Total
Insecticides
Carbary.1
Carbofuran
Chlorpyrifos
Dasanit
Diazinon
EPN
Ethoprop
Ponofos
Isofenphos
Methyl parathion
Organoclilorines
Parathion
Phorate
Terbufos
Toxaphene
Other
Total
Fungicides
TOTAL
34.3
56.9
8.2
6.6
4.4
2.6
1.2
4.2
1.8
12.5
1.2
133.9
2.1
9.3
0.7
1.1
0.5
0.2
5.5
0.7
3.2
1.6
6.1
2.2
0.2
0.5
33.9
0.03
167.8
26.4
47.9
14.9
13.1
8.9
1.8
0.4
11.6
1.4
3.3
11.3
2.3
143.3
0.1
5.5
3.4
0.2
0.7
5.6
0.9
0.2
0.2
3.7
7.7
0.3
0.8
29.3
0.1
172.7
58.2
83.8
24.3
10.4
1.4
8.2
1.6
7.7
2.4
8.0
1.1
207.1
2.1
9.9
0.5
0.8
0.1
0.2
5.0
0.2
3.9
0.6
5.8
2.5
0.1
0.3
32.0
0.02
239.1
52.3
69.7
54.9
20.7
2.1
8.3
0.3
21.7
3.5
3.3
5.1
1.5
243.4
0.2
5.2
3.9
0.2
0.7
5.1
1.3
*
0.1
3.8
8.7
0.6
0.3
30.1
0.1
273.6
none reported.
* = less than 50,000 acres.
I/ Includes nematicides.
ft
-------
TABLE 5
Soybean pesticide use, 1976 and 1982"s
Pesticide
Herbicides
Acres treated
1976 1982
Pounds (a.i.)
1976 1982
MILLION
Alachlor
Bentazon
Chloranlben
Dinoseb
Linuron
Metolachlor
Metribuzin
Naptalam
Trif luralin
Other
Total
Insecticides
Carbaryl
Disulfoton
Met homy 1
Methyl parathion
Parathion
Synthetic
pyrethroids
Toxaphene
Other
Total
Fumigants
Fungicides
TOTAL
18.7
5.3
3.7
4.2
10.4
8.5
3.1
24.2
3.9
82.0
2.9
0.2
0.9
0.7
0.4
0.5
0.3
5.9
0.5
1.2
89.6
18.3
11.6
4.4
5.6
8.3
7.1
23.6
3.3
33.6
19.9
135.7
2.0
0.1
1.7
3.4
3.4
1.9
1.3
13.8
-
0.2
149.7
30.7
3.8
4.4
3.7
6.2
5.2
3.9
21.1
3.2
81.1
3.7
0.2
0.5
0.7
0.3
2.2
0.3
7.9
2.0
0.2
91.2
30.7
8.0
5.9
3.5
5.8
12.9
10.2
4.4
30.7
11.9
125.2
1.5
0.1
0.7
2.6
0.6
3.7
1.7
10.9
0.1
136.2
* = less than either 50,000 acres or pounds (a.i.).
= none reported.
- 9 -
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TABLE 6
Cotton Pesticide Use, 1976 and 1982
Pesticide Acres treated (Million)
Herbicides
Cyanazine
Diuron
DSMA
Pluchloralin
Fluometuron
Linuron
MSMA
Norflurazon
Pendimethalin
Prometryn
Trifluralin
Other
Total
Insecticides
Az inphosmethy 1
Chlordimeform
Dicrotophos
Disulfoton
EPN
Met homy 1
Methyl Parathion
Monocrotophos
Sulpofos
Synthetic pyrethroids
Toxaphene
Other
Total
Dessicants and defoliants
Arsenic acid
DBF
Sodium chlorate
Other
Total
Fungicides
Miticides
TOTAL
1976
1.1
1.2
5.2
0.9
2.5
*
0.9
9.1
2.3
23.2
0.4
2.9
0.8
1.4
1.5
0.8
6.2
1.5
3.1
2.2
20.7
0.4
2.3
1.4
0.03
4.1
1.2
0.5
49.8
1982
0.7
0.6
0.6
0.3
3.4
0.4
2.4
0.6
1.0
1.0
5.6
2.1
18.7
1.0
2.3
0.6
*
1.1
0.9
3.8
0.4
0.6
4.7
0.6
0.5
16.5
0.5
1.5
0.9
0.7
3.6
0.5
0.1
39.4
Pounds ( a .
1976
0.4
1.5
5.3
0.4
1.8
*
0.7
7.0
1.2
18.3
0.2
4.4
0.3
1.8
6.1
0.6
20.0
1.5
_._
_«
26.3
2.9
64.1
1.7
3.4
3.3
*
8.4
3.5
0.4
94.7
i. ) (Million
1982
0.6
0.3
0.9
0.3
2.9
0.2
3.6
0.5
0.6
1.0
4.3
2.1
17.3
0.6
0.7
0.2
*
1.4
0.5
7.2
0.3
0.5
2.0
1.2
2.3
16.9
2.2
1.7
2.7
0.4
7.0
0.2
0.2
41.6
s none reported.
* = less than either 50,000 acres or pounds (a.i.)
- 10 -
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1.3 OCCURRENCE AND EFFECTS OF PESTICIDES IN AQUATIC
SYSTEMS
1.3.1 Occurrence
1.3.1.1 Ambient Studies
Since concern about the occurrence of organochlorine in-
secticides in water, sediments and biota was first raised in
the early 1960s, a tremendous amount of monitoring has been
done to determine the distribution of pesticides in aquatic
environments. Much of this information has been associated
with the development of more sophisticated and sensitive
analytical techniques and instrumentation for the determina-
tion of low-level contamination. A search of the literature
identified more than 140 published studies and reviews de-
scribing the results of ambient water monitoring programs
for pesticides since 1972 in the U.S. and Canada. Of these,
approximately 20 addressed field runoff, 30 were concerned
with ambient groundwater concentration, and the remainder
related the occurrence of pesticides in surface waters.
It is difficult to draw overall conclusions on the sig-
nificance of pesticide water pollution from the array of
ambient monitoring studies, but a number of observations can
be made:
1. Banned organochlorine insecticides such as DDT,
dieldrin, and Endrin continue to be detected in agri-
cultural soils, sediment, and aquatic organisms at
levels only somewhat less than those found before re-
striction of their use.
2. The more biodegradable pesticides such as the organo-
phosphorus and carbamate insecticides are found only
sporatically in ambient studies.
3. Those herbicides of higher solubility or less strong-
ly adsorbed to sediment may be generally increasing
in frequency of occurrence in U.S. surface waters.
There is, however, conflicting evidence on the extent
to which their presence significantly disrupts the
aquatic ecosystem. Many of these effects are subtle,
intermittent and/or difficult to monitor.
4. Pesticides, whether from manufacturing waste water,
field runoff loss, accidental spills or improper ap-
plication were the largest single documented cause of
fish kills between 1961 and 1974.
5. The majority of ambient groundwater studies have de-
tected pesticides, particularly herbicides, in areas
where agricultural use is extensive.
- 11 -
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A recent study by Baker (157) indicated that herbicide
concentrations in finished Ohio tap water were essentially
the same as in the rivers receiving agricultural runoff used
for water supply showing that conventional treatment does
little to remove these contaminants.
1.3.1.2 Directed Studies
In an effort to determine better the severity of water
pollution by pesticides a considerable number of directed
plot or field studies have been conducted. These differ
from the ambient monitoring studies in that they generally
involve intentionally adding or varying the application rate
of pesticides on crops or forests and observing subsequent
pesticide concentrations in the aquatic ecosystem. The
search of the recent literature identified about 80 such
studies with approximately 40 directed to field runoff, six
to groundwater and 31 to other surface waters.
A definitive review of pesticide concentrations in sur-
face runoff from agricultural fields has been done by
Wauchope (9). From 29 runoff studies involving 30 different
pesticides a range of 0 to 18.3% of the applied pesticides
was lost in runoff depending mainly on the type of pesti-
cide, application method, slope, and application timing with
respect to precipitation. The effects of these variables on
pesticide transport are described in detail in Section II.
For the majority of commercial pesticides the total losses
to runoff were 0.5% or less of the amounts applied.
1.3.2 Effects of Pesticides on Aquatic Systems
1.3.2.1 Toxicity Studies
A tremendous volume of literature has been produced con-
cerning the toxicity of various pesticides to aquatic
organisms. There is an even larger body of research con-
cerning the chronic or sublethal effects of pesticides on
aquatic systems. The most complete source for pesticide
toxicity information is the FDA Surveillance Index (155).
This i'nclex is continuously updated, and is intended to eval-
uate the potential health risk of individual pesticides.
Evaluations of 70 pesticides are currently included with
each evaluation consisting of a summary of past FDA monitor-
ing results as well as chemical, biological and
toxicological data.
- 12 -
-------
1.3.2.2 Effects on Water Quality
In addition to effects on aquatic ecosystems and biota
the presence of pesticides can affect other physical/chemi-
cal water quality parameters. In the case of herbicides,
the most commonly observed effect is a decrease in dissolved
oxygen concentration caused by the decomposition of aquatic
weeds exposed to herbicide-containing water (10,12.13).
The effects of pesticides on aquatic biota has been a
subject of considerable interest. Of significance is the
observation that algal photosynthesis is reduced by the
presence of many herbicides and even some insecticides at
concentrations well below accepted lethal or sublethal lev-
els (11, 13). Herbicides which are more toxic to aquatic
macrophytic plants than to algae may cause excessive algae
growth as nutrients become available from decomposing vege-
tation (12). Many effects of pesticides on aquatic systems
are subtle or indirect. For example, there is evidence that
organophosphorus pesticides adversely affect ammonium oxi-
dizing organisms in estuarine environments (14) allowing a
buildup of ammonia which is toxic to fish.
Over 130 recent studies of effects of pesticides on
aquatic macrobiota were identified. The effects vary widely
with type of pesticide and organism. In many studies ef-
fects on the ecosystem were very subtle (behavior changes,
elimination of ecological niches, creation of predator-prey
imbalance or direct changes in water chemistry).
- 13 -
-------
-------
Chapter 2
MODES OP PESTICIDE TRANSPORT
2.1 SELECTION OF MAJOR AND REPRESENTATIVE PESTICIDES
Pesticide transport mechanisms are highly dependent on
physical/chemical properties of the pesticide. Because
these properties are generally similar within a class of
pesticides, we, therefore, limit discussion to most widely
used pesticides of each class. From an analysis of the data
on pesticide usage presented earlier, combined with informa-
tion_on aquatic system impacts, the following pesticides and
pesticide classes were selected as a focus for reviewing
transport modes.
Insecticides:
1. Organochlorines (emphasis on toxaphene)
2. Organophosphorus (emphasis on methylparathion)
3. Carbamates (emphasis on carbaryl and carbofuran)
Herbicides:
1. Triazines (emphasis on atrazine)
2. Anilides (emphasis on alachlor)
.Some transport information is also included on paraquat (be-
cause of its special role in no-tillage production). In
addition, transport mode similarities with other important
pesticides are noted where appropriate.
- 15 -
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2.2 TRANSPORT TO AQUATIC SYSTEMS
The primary routes of pesticide transport to aquatic sys-
tems are:
1. Direct application.
2. In runoff: either dissolved, granular or adsorbed on
particulates.
3. Aerial drift.
4. Volatilization and subsequent atmospheric deposition.
5. Uptake by biota and subsequent movement in the food
web.
The relative importance of each of these transport routes
depends on many factors including the physical/chemical
properties of the pesticide, the method and timing of its
application, weather and climatic conditions, and the char-
acteristics of the land (soils, slopes, crops etc.). The
extent of soil adsorption and rate of degradation, in par-
ticular, have a strong influence on pesticide transport. A
recent laboratory study by Rao et.al. (156) has determined
adsorption coefficents and degradation rates as a function
of temperature and soil moisture for several of the pesti-
cide classes discussed below (carbamates, organophosphorus
and triazines). For this discussion the physical/chemical
characteristics of the pesticide have been chosen as the ba-
sis for initial consideration.
A thorough understanding of the dynamics of pesticide
transport is an important key for selecting the optimal pes-
ticide management strategy for a given situation. In most
cases proper selection will be highly site-specific. This
generalized review of the factors affecting pesticide trans-
port is therefore intended to serve as a basis for more
specific BMP selection guidelines.
2.2.1 Organochlorine Insecticides
Although most of these compounds have been banned from
use in the U.S., as seen in Table 3 significant amounts of
some materials, particularly toxaphene, are still in use.
The need for selection of BMPs to reduce transport from pre-
viously treated fields is also still a legitimate concern
(15,151).
16 -
-------
2.2.1.1 Volatilization and Drift
In the case of toxaphene there is strong evidence that
the principal mechanisms for field loss are aerial drift and
volatilization. In windspeeds of 5.6 km/hr (3.8 mi/hr) it
was found that only 47 percent of spray-formulated and only
14 percent of dust formulated toxaphene was deposited on
cotton fields from-aerial spraying (16). Dust formulations
of toxaphene are not currently utilized because of this low
delivery efficiency. Willis et. al. (17) observed that 26
percent of toxaphene applied to a mature cotton canopy vola-
tilized within five days. Volatility rates were greatest
during mid-afternoon peak temperatures, but volatility was
also high when leaves were drying after heavy dew or light
rain. Several other studies have shown similar or greater
volatilization losses of organochlorine pesticides (18, 19,
20, 21). These studies indicate that the extent of volati-
lization is affected by air and soil temperature, humidity,
and air circulation rates.
The impact of the volatilization transport route on
aquatic systems has been difficult to document. It has,
however, been estimated that aerial fallout may be a much
greater contributor of toxaphene to aquatic systems than the
more obvious field runoff. A 1976 study in the Mississippi
Delta found high atmospheric concentrations of toxaphene and
other pesticides in cotton growing areas (37). Toxaphene
was present throughout the year with highest concentrations
between June and October. Concentrations as high as
1946ug/m(3) were observed. Willis et. al. (17) estimated
volatile losses were 3 or 4 times as great from a single ap-
plication as runoff losses from the entire year.
2.2.1.2 Runoff and Soil Leaching
In a study of toxaphene washoff from cotton plants it was
found that only an average of 1.3% of applied toxaphene was
washed from the plant canopy by heavy simulated rainfall
(22). This agrees well with Wauchope's estimate (9) that
about one percent of applied organochlorine insecticide is
lost in runoff waters. Within the runoff transport mecha-
nisms -it is generally agreed that most toxaphene is lost in
the sediment phase rather than dissolved in runoff due to
its low solubility (0.4 ppm) and strong soil adsorption
properties (9, 8). Willis et.al. (151) observed that storm
toxaphene yields were linear functions of storm sediment
yields from a 18.7 ha watershed.
Because toxaphene is relatively insoluble and strongly
adsorbed, the potential for groundwater contamination is
- 17 -
-------
low. One field study indicated that nearly all toxaphene
was confined to the top 30cm of a Houston black, clay after
ten years (23). In another study, however, where excessive
(lOOkg/ha) amounts were applied directly to a sandy-loam
soil, toxaphene the underlying groundwater for the entire
year of observation (24). Thus, the potential for toxaphene
movement to groundwater appears to be present at least in
the case of spills, 'improper application or land disposal.
2.2.1.3 Biotic Transport Modes
Uptake and movement through the food web deserves special
mention as a transport mechanism for toxaphene. As with
other organochlorine insecticides, the combination of slow
biodegradability and high fat solubility result in uptake
and biomagnification(increasing concentration with trophic
levelJin both aquatic and nonaquatic organisms. Although
the actual percentage of toxaphene transported to aquatic
systems through this route is not known and may be relative-
ly small, it is this portion which may be most ecologically
significant as nearly 100% of the pesticide transported by
this route will directly impact aquatic biota. There is ev-
idence that toxaphene is less biomagnified in aquatic
ecosystems than other organochlorine insecticides (26).
2.2.2 Organophosphorus (OP) Insecticides
As shown in Table 1 the most common organophosphorus
(OPs) insecticides in use are terbufos, fonofos and methyl
parathion. The chemical structures of all three of these
compounds are fairly similar, each being part of the class
of compounds known as phosphoisothioates. With some excep-
tions, they have been found to have similar modes of
transport.
A primary characteristic which differentiates the OPs
from the organochlorines in terms of transport is their per-
sistence in the environment. While the organochlorines have
half-lives in the environment on the order of years, the OPs
degrade relatively rapidly. Estimates of half-lives for
differ-ent OP compounds, vary as do estimates for the same
compounds, but most are in the range of 1-8 weeks depending
on the contact medium (soil, atmosphere, water) (8, 27, 28).
Thus, the transport of OP insecticides to aquatic systems
and the subsequent impact on these systems are limited by
the relatively short life of these chemicals.
18 -
-------
2.2.2.1 Aerial Drift and Volatilization
As with the organochlorines, the principal modes of
transport of OPs appear to be aerial drift during applica-
tion and volatilization from plant and soil surfaces. Adair
et al. found that when using methylparathion applied aerial-
ly from 1.52 meters, less than 40 to 50 percent of the
applied material was deposited within the target area (29).
Since most OPs are used on cotton which is often aerially
treated, this represents a major transport mode. A review
by von Rumker et. al. (30) indicates that similiar losses
from drift occur from aerial spraying of any insecticide.
Ultimately, however, the percentage of drifted material
which reaches aquatic systems and the resulting aquatic con-
centrations depend on the proximity and morphology of
downwind water bodies.
Volatilization is also a very important transport mecha-
nism for OPs. Reviews by Hague and Freed (21) and Spencer
et. al. (31) indicate that between one-third and one-half
of OPs that reach the target area volatilize. The actual
amount depends on temperature (32), humidity, air circula-
tion, and soil moisture (33). In hot weather regions such
as the cotton growing areas of Mississippi half-lives of me-
thyl parathion on soil and plants have been observed to be
as low as one-half hour (34). Atmospheric OPs may be found
in vapor phase or adsorbed (35). A number of studies have
detected atmospheric concentrations of OPs both in treated
and untreated areas (36, 37, 35). From these it can be con-
cluded that while airborne residues are invariably found
near sprayed areas during the growing season, their presence
also covers large areas remote from treatment. Unlike toxa-
phene, atmospheric methyl parathion was observed at
significant levels only during July, August and September
because of its more rapid biodegradation (37). However,
very high atmospheric concentrations (up to 2060ug/m{3})
were observed during these three months. The impact of OPs
on aquatic systems through the volatilization mode of trans-
port is difficult to assess because of the diffuse nature of
the input. Studies of concentrations in rainfall are neces-
sary to determine whether redeposition is a significant
source of OPs and other pesticides to aquatic and terrestial
ecosystems.
2.2.2.2 Runoff and Soil Leaching
While the amount of OPs available for transport to aquat-
ic systems through runoff and leaching is greatly limited by
drift and volatile losses and by the relatively quick degra-
dation rates of these compounds, runoff losses may be
harmful to aquatic systems because they enter the system as
- 19 -
-------
concentrated pulses. Also, little information is available
on whether some degradation products may also damage aquatic
ecosystems. Wauchope (9) cites a range of 0.008% to 0.25%
of applied methylparathion lost in runoff. A Canadian study
showed high parathion loadings in drainage waters from near-
by agricultural lands where high application rates were used
(38). No attempt was made to quantify what percentage of
material was being lost by this route however. It would ap-
pear that the percentage of materials lost in runoff
(adsorbed or dissolved fraction) is indirectly, but perhaps
strongly, correlated with soil type because soil type has
been shown to affect the persistence of OP compounds in
soil. For example, the persistence of parathion in soils is
increased by the presence of clays, organic matter or low pH
(35). Baker et. al (55) found that the OP, fonofos, was
lost primarily in the adsorbed phase, and losses could be
reduced by erosion reducing tillage methods. Modeling ef-
forts for methylparathion predict that about 90 percent of
runoff losses are in the dissolved phase (143).
2.2.2.3 Leaching to Groundwater
Some information exists on the leaching of OPs through
the soil profile to groundwater. The moderate solubilities
and moderate soil adsorption coefficients for these com-
pounds place them in a low to intermediate range for
groundwater contamination potential. Field studies have
shown leaching of parathion through 12-18 inches of soil
profile (39,40). King and Me Carty (41) have shown that the
leaching of parathion is greatly influenced by soil type
with considerably less leaching occurring on clay soils.
2.2.3 Carbamate Insecticides
As shown in Table 1 the most heavily used insecticides of
this group of chemicals are carbofuran (on corn) and carba-
ryl (on soybeans). These compounds are both
methylcarbamates, and are therefore structurally similar.
However there are some differences in chemical properties
which result in somewhat different modes of transport. One
example is the difference in solubility (42) (carbofuran =
700 ppm,, carbaryl = 40 ppm) which has important implications
for runoff transport. Another is vapor pressure (carba-
ryl>carbofuran) which affects volatile losses.
- 20 -
-------
2.2.3.1 Runoff and Soil Leaching
Despite the differences in solubility, research results
indicate that both carbamates are lost almost entirely in
the dissolved phase of runoff (43). Because of its higher
solubility carbofuran is more susceptible to runoff losses.
Over a period of three months covering eight runoff events
only 0.15% of applied carbaryl was lost (43), while other
studies by Caro et. al. (44) have shown seasonal runoff
losses of carbofuran ranging from 0.47 to 1.9 percent on
silty loam soils. Studies on claypan soils showed annual
maximum losses from single runoff events ranging from 1 to
14% of applied .carbofuran (45). Runoff concentrations
ranged from 298 to 600 ppb. Because the 96-hour LC(50)
ranges from 80 to 1180 ppb for ten fish species, runoff
losses of these magnitudes clearly constitute a serious
threat to neighboring aquatic ecosystems (8).
2.2.3.2 Drift and Volatilization
Airborne losses of carbofuran either from drift or vola-
tilization are considered to be quite small. This is due to
both low vapor pressure (6.5x10-5 torr) and the fact that
carbofuran is usually applied to the soil in a granular
form. Even with granules drift losses can be significant
(up to 50%) if application is made under windy conditions
(12 mi/hr) (8). There is no evidence of volatile losses of
carbofuran when applied for agricultural purposes regardless
of application method or timing.
Airborne losses of carbaryl can be quite high. Its vapor
pressure of 2.1x10-5 torr makes it about 3 times as volatile
as carbofuran. Stewart et. al. (46) classified carbaryl as
only slightly less volatile than methyl parathion or toxa-
phene, indicating that volatile losses in the range of 10-30
percent might be expected. In addition, carbaryl is fre-
quently applied as a dust formulation which makes it
susceptible to large drift losses whether applied by aerial
or ground equipment.
The carbamates are fortunately very short-lived in the
environment, a consideration which lessens the effect of
their acute toxicity to aquatic organisms. Carbaryl has
been shown to persist for up to three weeks in soil (47) and
one - two weeks in aquatic systems (28), Carbofuran is
longer-lived in soil systems (16 weeks) but is degraded as
rapidly as carbaryl in aquatic systems (48)
Movement through the food web is not considered an impor-
tent transport mechanism for carbamates because of their
rapid biodegradation and fat insolubility. Another study
- 21 -
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showed that the aquatic degradation of carbaryl by
hydrolysis is very pH and tejnperature (Q{lO}=2.9) dependent.
Little hydrolysis occurs at pH 6, whereas the half-life var-
ies from 10.5 days at pH 7 to 1.3 days at pH 8 (142).
2.2.4 Triazine Herbicides
Triazine herbicides include such products as atrazine, cya-
nazine, metribuzin, prometryn, propazine, secbumeton,
simazine, and terbuthylazine. Of these atrazine is by far
the most extensively used on cropland, and thus will be em-
phasized in this discussion of transport modes.
2.2.4.1 Runoff and Soil Leaching
Runoff losses of triazine herbicides from cropland have
been a major concern and have been studied under a wide va-
riety of conditions. Wauchope (9) cites a range of 0.2 to
16% of applied atrazine lost in runoff depending on condi-
tions. The most important factors affecting runoff losses
appear to be topography and soils (49,50), land management
practices (51,52,53), rainfall, intensity (53), application
rates, and, perhaps most importantly, the time interval be-
tween application and subsequent runoff events (54,51).
There is evidence that other factors such as soil pH and or-
ganic matter content may also influence runoff losses by
affecting the partitioning between adsorbed and dissolved
phases (50). Atrazine is more strongly bound by organic
matter and acidic soils.
Although the concentration of atrazine is invariably
higher in the adsorbed phase of runoff, there is general
agreement that the majority of atrazine is lost in the dis-
solved phase due to the high ratio of water to sediment in
runoff from cropland (54,49,52). Hall (54) observed that
eight times more atrazine was lost in the soluble phase than
in the adsorbed phase of runoff at a 2.2 kg/ha application
rate and over four times more at a 4.4 kg/ha rate. In these
field studies about 90% of the runoff loss of atrazine oc-
curred during the first month after application. Studies by
Baker "and Johnson (53) indicate that seasonal losses can be
kept under 5 percent in years when the application-runoff
interval is greater than two weeks. Losses were 16 percent
when a storm occurred immediately after application.
Ritter et. al. (51) noted that much more atrazine was
lost from surface-contoured fields than from ridge-contoured
fields. Baker et. al. (55) found that cyanazine losses were
virtually identical from either conventionally tilled plots
- 22 -
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or from a series of plots in various forms of conservation
tillage (till-plant, chisel plow, disk-plant, ridge-plant
and fluted coulter). The decreases in runoff volume and
soil loss from the conservation tillage systems were negated
by the increased cyanazine runoff concentrations. This was
attributed to the effect of surface residue intercepting the
herbicide spray before it could reach the soil surface, thus
preventing soil adsorption. This is substantiated by the
work of Martin et. al. (148), who found that 32 to 43 per-
cent of triazines or anilides were washed from corn residue
by 5mm (0.2 in) of simulated rainfall. Other studies
(56,57) have noted greater atrazine losses from no-till
plots versus conventional tillage for the same reasons. In
contrast Triplett et. al. (52) observed somewhat lower loss-
es from no-till corn. Triplett et. al. (52). surmised that
this was due to moderate intensity storms which produced no
runoff from several of the no-till plots. The other studies
used high intensity simulated rainfall. Likewise, in a re-
cent three year natural rainfall plot study, Hall et.al.
(149) found that cyanazine runoff losses were reduced be-
tween 85 and 99 percent from no-till verses conventionally
till corn. In this case, the large reduction were attribut-
ed to the use of a "living mulch" surface of crownvetch and
birds foot trefoil which minimized the residue interception
problem. The effect of surface residue on herbicide runoff
is further clouded by a more recent plot study by Baker et.
al. (126) which showed that herbicide runoff losses were
consistently less from plots with surface corn residue.
There was no significant difference in runoff loss between
plots where atrazine and alachlor were applied over the
residue or where the herbicides were applied first and then
covered with residue.
A recent discussion by Baker and Laflen (147) explains
these seemingly conflicting results. They note that, if
herbicide application on crop residue is followed by a light
rainfall, herbicides washed off the crop residue infiltrate
into the soil making them less susceptible to loss in future
runoff events than herbicides applied to bare soil. If, on
the other hand, an intense runoff-producing storm is the
first event after the herbicide application, then more her-
bicides will be lost from reduced tillage than from
conventional tillage because the free herbicides washed from
the crop residue will be very readily carried in surface
runoff.
In one of the very few actual watershed studies on atra-
zine inputs to aquatic systems Wu et. al. (145) found annual
atrazine stream loading rates ranging from 1.2 to 2.7 g/ha
for seven 16 to 254 ha watersheds. These loading rates rep-
resented 0.05 to 2.0 percent of the amounts applied. In
contrast to several of the field and plot studies atrazine
was detected in stream flow from runoff events throughout
-------
the year. In fact, in the drought year of 1977 the majority
of stream input occurred during the following winter and
spring (i.e. 6 to 9 months after application). Also of sig-
nificance was the finding that daily flow weighted mean
concentrations in' the streams never exceeded 40 ug/1 during
the three years of study, and monthly flow weighted means
ranged from <0.01 ug/1 to 8 ug/1, much lower concentrations
than generally observed from plot and field studies.
A summary of atrazine runoff losses is shown in Table 7.
Of particular significance is the range of runoff water her-
bicide concentrations observed in these studies. While
atrazine is considered only moderately toxic to fish, con-
centrations in the 0.02 to 0.5 mg/1 range have been shown to
disrupt aquatic ecosystems by eliminating phytoplankton and
submerged macrophyte species (58,150).
The potential .for groundwater contamination by triazines
has also been a major research concern in recent years.
Several groundwater monitoring studies have revealed the
widespread presence of these compounds at detectable levels
(59,60). The extent to which leaching occurs depends on
several factors including the application rate, soil compo-
sition, soil moisture, plant uptake, and management
practices (8).
In soil column leaching experiments atrazine penetrated
six to eight inches in two days with maximum movement occur-
ring in light textured sandy loams at high pH (61).
A field study (97) with well-drained sandy loams in Ne-
braska found atrazine levels ranging from 0.01 to 8.29 ug/1
in groundwater 5 to 10 meters below irrigated corn. Season-
al fluctuations indicated some soil dissipation of atrazine.
Laboratory studies ruled out microbial degradation as a sig-
nificant dissipation mode.
The adsorption of atrazine is maximized by the presence
of soil organic material and acidic clay soils (50). Scott
and Phillips (62) determined that the movement of atrazine
through a silty clay loam increased by a factor of four as
soil moisture content was increased from 25 to 38% indicat-
ing the strong influence of soil moisture on leaching
potential.
2.2.4.2 Drift and Volatilization
Drift losses of atrazine depend almost entirely on the
application method, ranging from negligible for incorporated
ground equipment application to about 40 percent when aeri-
ally applied (8, 30). Even applications by ground equipment
- 24 -
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TABLE 7
Atrazine Runoff Losses Summary
Amount
Applied Type
(Kg Al/ha) Application
3.361 surface with
simulated
rainfall3
2.22 surface13
1.681 Incorporated
rainfall
3.361
3.361
2.22 surfaced
4.52
3.36' surface6
2.24* surfacef
1.12-3.362 incorporated9
2.092 surface (0)"
2.092 with (375)"
2.092 simulated (750)"
2.092 rainfallh (1500)"
3.36s incorporatedi
3.81s
1.54s
3.36s
4.03s
1.45s
1.7s surface-]'
1.0s
1.0s
1 Duration of experiment was 1
Duration of experiment was 5
1 Duration of experiment was 58
* Kg/ha corn residue.
5 Duration of experiment was 90
s Duration of experiment was 1
a White et al. (1967).
b Hall eFYT (1972).
c Bailey et al. (1974).
d Hall (1974TT
e Ritter et al. (1974).
f Baker and" 3ohnson (1977).
9 Triplett et al. (1978).
h Baker et aT.~Tl982).
i Leonard et al. (1982).
j Uu et al. (1983).
Average Loss in Runoff
Slope (%) (% Application)
6.5
14
2.2
3.6
2.5
5.7
14
10-15
12-18
8-22
5
5
5
5
4
4
4
3
3
3
5
5
5
hour on
months
2
(2 - 7.3)
2.5
6.44
12.47
13.3
10.18
5.0
4.8
2.7-16.0
>5
0.02-5.7
5.71
3.37
2.54
0.97
1.9
0.2
0.7
0.8
0.2
0.3
0.37
0.18
0.14
fallow lands.
on corn crop.
Concentration
in Runoff
Water (ppm)
0.16-8.08
0.0-0.8
0.0-3.3
0.0-7,9
0.0-11.1
0.0-4.0
0.0-2.3
0.05-4.6
1.17-4.91
0.10-0.48
0.14
.10
0.09
0.09
0-0.20
0-1.90
0-0.10
0-0.16
0-0.33
0-0.04
^
-
days on corn crop.
days on corn crop.
year on
_
corn crop.
25 -
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can lead to drift losses of 50 percent under windy
conditions (53).
Little information exists on volatile losses of triaz-
ines. The greatest amount of volatilization appears to
occur when application is to the surface rather than incor-
porated and when application is made to dry, warm soils (8).
The extent of volatilization appears to be very temperature
dependent. One study measured losses of 40 percent and 80
percent at soil temperatures of 35 c and 45 c respectively
(64).
Atrazine and other triazines kill weeds by inhibiting
photosynthesis. This mode of action creates the potential
for subtle aquatic ecosystem effects by eliminating sensi-
tive algal and macrophytic species (160). Atrazine has been
shown to be toxic to fish in the 0.5 to 10 ppm range (65)
within which fall runoff concentrations observed under worst
case conditions.
The persistence of atrazine in the environment depends on
several of the factors previously mentioned in connection
with transport routes including: method of application
(surface applied or incorporated), soil conditions and ap-
plication rate. Hague and Freed (21) have noted persistence
in soil of four months to a year. Greater persistence was
noted when the material was incorporated in acidic or organ-
ic soil. Persistence increases with the clay content of the
soil and serious carryover problems can occur from one crop
season to the next when the clay content is greater than 30
percent (70). Recent work by Gressel et. al. (66) has shown
that N-dealkylaton by triazine resistant plants may be a
primary degradation route. Little information on persis-
tence in aquatic systems is available, although as opposed
to soil systems photodecomposition and hydroxylation are be-
lieved to be the major degradation mechanisms (67). There
is evidence that significant decomposition of atrazine oc-
curs by hydrolysis reaction in acidic waters (68). There is
general agreement that triazines are not biomagnified to any
appreciable degree, with the greatest accumulation noted in
certain species of triazine resistant algae (8, 69).
In summary, the persistence and degradation of atrazine,
and to some extent other triazines, in agricultural soils
are fairly well understood, but less is known about their
persistence in aquatic environments. The degradation rate
in aquatic environments has important implications for de-
signing management practices to control pollution by
triazines. Based on the frequent detection of atrazine in
surface and groundwaters, there is little reason to believe
that it is less persistent in aquatic systems than in soil
systems. Therefore, management practices to control triaz-
ine inputs to aquatic systems need to be effective through
entire seasons.
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2.2.5 Anilide Herbicides: Alachlorr Propachlor
As noted in the discussion on pesticide usage, alachlor
has become a major herbicide on both corn soybeans and its
use appears to be increasing rapidly on both crops (71). In
contrast usage of propachlor has dropped by almost 75 per-
cent since 1971 (Table &3.). A search of the literature
revealed very little research information on alachlor trans-
port mechanisms.
Alachlor's solubility in water is 242 ppm or nearly eight
times higher than atrazine. On this basis it would be ex-
pected that, like atrazine, most runoff losses would be in
the dissolved rather than the adsorbed phase. Research by
Baker et. al. (55) has verified this assumption. Bulk (dis-
solved plus adsorbed) runoff concentrations ranged from 75
to 184 ug/1 with sediment concentrations of about one mg/1
from small plots with simulated rainfall. An average of 7.9
percent of the applied amounts were lost. Tillage practices
had no significant effect on runoff losses. Baker et. al.
(126) observed alachlor losses in surface runoff ranging
from 1.0 to 8.6 percent from heavy simulated rainfall with
losses decreasing with increasing crop residue. Percentage
losses were somewhat greater for alachlor than for atrazine
on the same plots. The solubility of propachlor is 580 ppm
giving it even greater potential for loss in the dissolved
phase and leaching to groundwater. Hitter et. al. (51)
found that 3.1 percent of applied propachlor was lost in
runoff in the first month following application. Bulk run-
off concentrations were as high as. 1.7 ppm.
The small watershed studies by Wu et. al. (145) showed
very small watershed losses of alachlor (<0.1 percent).
Overall stream loadings were lower than for atrazine even
though alachlor was used at higher rates in the watershed.
Stream concentrations of alachlor seldom exceeded lug/1.
Alachlor is normally applied.either in granular form or as
an emulsion applied to the soil surface. No information was
found on drift or volatile losses of alachlor or on its soil
leaching behavior.
2.2.6 Bipyridylium Herbicides: Paraquat
Paraquat deserves special mention because of its role in
conservation tillage and no-till corn production since the
acreages under these practices are large and are projected
to increase dramatically in the near future. Paraquat's
role in conservation tillage systems is to destroy either
cover crops or growing annual weeds at crop planting or pri-
or to emergence.
- 27 -
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A series of field experiments by Smith et. al. (72)
showed a range from 0.9 to 18.3 percent of applied paraquat
lost in runoff. This is probably a large overestimation of
runoff losses because the application in these experiments
was directly to soil, while in agricultural use,, application
is primarily to foliage. Another study revealed runoff
losses of 1.28 percent (73). All losses were in the sedi-
ment bound phase, because as a positively charged ion,
paraquat is strongly bound to the negatively charged soil
particles.
Paraquat is usually ground applied with water or liquid
fertilizer at 30 to 50 gal/acre. Large droplet sprayers are
used to minimize the amount of drift (8). Byass and Lake
(74), however, have shown that drift losses of paraquat of
only 0,1 percent of the applied amounts could cause damage
to down-wind plants. Paraquat is essentially nonvolatile,
and volatilization losses from agricultural fields are neg-
ligible (75).
The complex question of whether paraquat adversely im-
pacts aquatic systems has been well addressed by Shoemaker
and Harris (8). Although paraquat in its free form is high-
ly toxic to both plants and animals, it is rapidly and
apparently permanently bound to clay materials in soil or
sediments. There is strong evidence that clay-adsorbed pa-
raquat is not biologically available. With the exceptions
of soils with very high organic or sand content even the
least adsorptive soils can strongly bind many years of para-
quat applications (76). Erosion and transport of such
paraquat containing soil particles to aquatic systems could
cause contamination until the available paraquat was redis-
tributed onto deactivating clays. Although runoff losses of
paraquat are substantial, no documented cases of adverse im-
pacts of paraquat in aquatic systems have been reported. It
has been assumed that leaching of paraquat through the soil
column can not occur because of the strong soil adsorption.
However, recent work by Vinten et. al. (125) shows that pa-
raquat can move a considerable distance through the soil if
adsorbed to mobile clay colloids. The researchers suggest
that this same transport mechanism is also possible for oth-
er soil adsorbed pesticides.
Thus/ field losses of paraquat appear to be relatively
innocuous to aquatic systems providing little incentive for
control. The greatest hazard from paraquat use appears to
be to farm workers and to applicators who might be exposed
to unbound paraquat from handling and drift.
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Chapter 3
BEST MANAGEMENT PRACTICES FOR REDUCING PESTICIDE
DELIVERY TO AQUATIC SYSTEMS
Having established the modes by which various classes of
pesticides are lost from agricultural lands and reach aquat-
ic systems, and having discussed the subsequent impact on
these systems, it is possible to consider the agricultural
options available for protecting water quality. Agricultur-
al options for pesticide pollution control fall into four
general categories:
1. Soil and Water Conservation Practices (SWCPs);
2. Increasing efficacy of pesticide application tech-
niques;
3. Integrated Pest Management systems which minimize the
amounts of pesticides needed (IPM);
4. Substitution of less biotoxic and/or less persistent
pesticides where effective alternatives exist.
The remainder of this section provides a brief discussion
of how each of the four classes of pesticide pollution con-
trol options listed above can function to reduce pesticide
losses to aquatic systems. With this background, an analy-
sis of optimal best management system approaches will be
presented for some major U.S. agricultural crops (corn, soy-
beans, cotton, tobacco, alfalfa and tree fruits).
3.1
SWCPS
3.1.1 Non-structural Practices
3.1.1.1 Conservation tillage
The largest and most important controversy regarding the
pesticide pollution control effectiveness of SWCPs has cen-
tered around conservation tillage systems. There appears to
be agreement that into the near future these systems may re-
quire somewhat greater pesticide usage (particularly
herbicides) than conventional tillage systems (78). Coun-
teracting the greater pesticide usage are the reductions,in
- 29 -
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soil loss and often in runoff volume which accompany these
practices. A recent review of sediment control practices
(77) indicates that conservation tillage systems reduce soil
loss by 60 to 99 percent depending on such factors as per-
cent surface coverage, soil type, slope, and crop. No-till
reductions normally range between 85 and 99 percent. Thus,
strongly bound pesticides such as paraquat and toxaphene,
which are lost primarily in the sediment-adsorbed phase of
runoff, should be sharply reduced by conservation tillage.
As with other sediment-bound materials such as phosphorus,
loss reductions are predicted to be less than soil loss re-
ductions because the soil particles which are lost from
SWCPs are the finer fractions which have relatively greater
amounts of adsorbed materials (77,151).
Runoff volume is usually reduced by conservation tillage
systems. Changes have been reported to range from -89 per-
cent to +10 percent. No-till systems reduce runoff volume
less than other conservation tillage systems, and in a few
cases no-till runoff volumes have been greater than from
conventional tillage (77). On this basis it would be ex-
pected that runoff losses of pesticides that are primarily
in the dissolved phase, such as carbamates, triazines and
anilides, would usually but not always be significantly re-
duced. However, as noted earlier, in several studies equal
or greater amounts of triazines were lost from conservation
tillage than from conventional tillage (55,56,57). The ex-
pected control of pesticide loss from control of runoff and
soil loss is often negated by higher concentrations in the
runoff. Surface residue may intercept a portion of the pes-
ticide application before it reaches the soil surface,
thereby rendering it more susceptible to runoff loss. Also,
in these experiments application rates were identical for
conventional and conservation tillage plots whereas recent
work shows that for corn and soybeans more herbicides may be
used in conservation tillage systems, particularly notill
(Table 8) (78).
These data show that, while no-till herbicide usage is con-
siderably greater than conventional, there are no
significant differences in overall herbicide use between
other reduced tillage systems and conventional systems for
corn or soybeans. As noted earlier, conservation tillage
systems necessitate different herbicide use patterns (use of
contact herbicides and broad spectrum herbicides). Also,
conservation tillage systems often preclude the possibility
of incorporating pesticides into the soil. Therefore, the
pesticides are more readily available for transport in run-
off. Higher application rates may be necessary to achieve
proper pest control. This latter effect is seen in the con-
trol of root-worm infestation in corn where insecticide
application rates are considerably higher for no-till sys-
tems.
- 30 -
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TABLE 8
Per-Acre Herbicide Cost for Corn and Soybean Production By
Tillage System
Corn: Ten Major Producing States
No-till
Reduced-till
Conventional-till
3.50
3.38
3.00
Soybeans
No-till
Reduced-till
Conventional- till
Midwest
3.23
1.86
2.03
Midsouth
2.00
1.74
1.45
Southeast
1.68
1.46
1.38
3.1.1.2 Contouring
Contour farming reduces soil erosion by slowing water
movement and allowing increased infiltration. It is most
effective on fields of moderate (<8%) slope which are free
of depressions and gullies. Runoff volumes may be reduced
15 to 55 percent depending on crop and soil type (83). Sim-
iliar reductions of dissolved pesticides would be expected,
however, a study in western Iowa found that nutrient reduc-
tions relative to noncontoured fields were somewhat less
than runoff reductions (80). This suggests that the degree
of runoff reduction may constitute an upper limit for sur-
face runoff reduction of pesticide transported in the
aqueous phase of surface runoff. Another study (51) found
that atrazine loss was greatly reduced by both surface and
ridge contoured fields relative to noncontoured fields.
Greater reductions were noted for ridge-contoured fields
which allowed more "ponding" of runoff between rows with
subsequent increases in infiltration. The increased infil-
tration from contouring may increase the potential for
groundwater contamination for those pesticides which are
relatively mobile in soil.
- 31 -
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3.1.1.3
Stripcropping
Stripcropping has potential advantages for reducing pes-
ticide runoff losses by reducing erosion and runoff volumes.
The extent of reduction is dependent on soil type, slope,
types of crop and the presence of complementary SWCPs. In
addition, there is evidence that Stripcropping can reduce
insect, nematode, and weed problems, thus affecting the
amounts of pesticides required (114).
3.1.1.4 Grassed Waterways
Grassed waterways can be considered either structural or
nonstructural depending on how much earth-moving is required
for construction. The primary function of grassed waterways
is to prevent the formation of gullies in natural or con-
structed field depressions which transport surface runoff
from the field. In this capacity they should have little
effect on pesticide losses because pesticides are generally
not directed to the waterway. A secondary function of
grassed waterways is to slow runoff velocity allowing sedi-
ment deposition within the field and to otherwise filter
sediment particles from runoff (77). In this capacity some
reduction in sediment-adsorbed pesticides would be expected.
3.1.1.5 Cover crops
The purpose of cover crops is to provide vegetative cover
and erosion control during the nongrowing season. The ex-
tent of erosion control obtained depends on the
precipitation patterns of a particular region during the
nongrowing season and on the amount of cover crop establish-
ment before winter freeze. In northern areas or after late
crops like soybeans, little fall growth occurs and cover
benefits may be negated by the additional fall tillage often
necessary. Large-scale studies in the Black Creek, Indiana
project (81) documented some erosion reduction from cover
crops in this region. A Missouri study found that a rye
cover crop with no-till corn reduced soil loss by over 95
percent compared to conventional- till continuous corn (82).
This probably represents the upper limit of possible erosion
reductions from the practice. Runoff volumes should also be
reduced both as a function of increased infiltration and
evapotranspiration by the cover crop, although no quantita-
tive data are available. A search of the literature found
no actual field studies which determined effects of cover
crops on runoff losses of pesticides; however, from the dis-
cussion above it would be expected that losses could be
somewhat reduced for pesticides lost either in the sediment-
- 32 -
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adsorbed or runoff phase which are sufficiently persistent
to still be available for loss into the nongrowing season.
3.1.1.6. Filter Strips
Filter strips have little or no effect on erosion but can
reduce the sediment delivery ratio to aquatic systems by
slowing runoff velocity and filtering sediment. Karr and
Schlosser (42) found that vegetative filters could effec-
tively filter sediment from both sheet and shallow channel
runoff. Their sediment holding capacity is very limited and
thus must be used in conjunction with erosion-reducing prac-
tices to be effective. Variables which affect their utility
include: filter width, degree and homogeneity of slope, veg-
etative type, sediment size distribution and concentration,
and runoff application rate (83). On this basis filter
strips could be expected to reduce the delivery of sediment-
bound pesticides to aquatic systems.
3.1.2 Structural Practices
3.1.2.1 Terraces
Terraces are structures consisting of a combination ridge
and channel constructed across the slope (83). They can be
divided into two general classes: graded terraces which di-
vert water to a grassed waterway or to some other nonerosive
drain; and level terraces which hold water on the field in-
creasing infiltration and allow eroded soil to be
redeposited. The range of soil loss control achievable by
terracing has been observed to be 50 to 98 percent depending
on climate, slope and soil type (77). Similar reductions in
runoff volumes have been observed with greatest reduction
occurring in drier areas with level terraces. It has been
noted that terraces should reduce losses of strongly ad-
sorbed pesticides such as paraquat and organochlorine
insecticides and that the degree of .sediment reduction
should be an upper limit (72). A study in western Iowa on
pesticide loss from terraces and contoured fields produced
results which suggest that less discharge of moderately ad-
sorbed pesticides such as atrazine and organophosphorus
insecticide occurred from terraced watersheds than from con-
tour planted watersheds (84). Most terracing is constructed
on long, moderately steep slopes where much of the infiltra-
tion reappears as stream baseflow. Therefore, while edge of
field dissolved pesticide losses may be reduced concomitant
with runoff volume reductions, the extent to which actual
pesticide inputs to nearby aquatic systems are reduced is
unknown.
- 33 -
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The increased infiltration accomplished by terracing
greatly increases the potential for pesticide leaching to
groundwater, particularly in more humid regions such as the
Northeast, Southeast and Pacific Northwest.
3.1.2.2 Sediment Basins
Sediment basins have no effect on edge of field soil loss
but have been shown to be highly effective in trapping sedi-
ment particles before they can reach water resources of
ecological, economic or recreational importance. The Black
Creek Indiana project (81) showed that sediment basins could
effectively trap fine particles which are the most difficult
to control on the field (less than 50 microns in diameter).
Several other studies have found a range of 65 to 98 percent
efficiency in sediment trapping (85,86,87) depending on mean
flow velocity, particle size distribution and reservoir ge-
ometry.
Clearly, sediment basins primarily affect sediment ad-
sorbed pesticide inputs. Their effect on dissolved
pesticide transport will depend on the relative magnitude of
the basin detention time and the aquatic half-life of the
pesticide. Some additional pesticide removal may occur as a
result of uptake and/or degradation by biota within the sed-
iment basin (89,90). A search of the literature found no
studies on the pesticide removal efficiencies of sediment
basins receiving cropland runoff. Sweeten and Drire (88),
however, observed that evaporation ponds adjacent to Texas
feedlots effectively reduced pesticide loss in feedlot run-
off.
3.1.3 Summary of Effect of SWCPs on Pesticide Inputs to
Aquatic Systems
A summary of the effects of various SWCPs on surface runoff
volume, soil erosion and sediment delivery ratio is shown in
Table 9. Practices which reduce sediment inputs to aquatic
systems either by reducing erosion or reducing the sediment
delivery ratio will decrease aquatic inputs of strongly
bound pesticides. Adsorbed pesticide reductions will gener-
ally be somewhat less than sediment reduction because of the
enrichment of pesticides in the finer sediment fractions
which are less effectively controlled by most SWCPs.
Pesticides which are lost primarily in the soluble phase
of surface runoff can be controlled by runoff reducing prac-
tices. The extent of pesticide loss reduction should be
proportional to the reduction in runoff volume. Possible
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exceptions to the above are conservation tillage systems
where decreases associated with runoff reductions can be
offset by increased availability of pesticides applied _ to
sod or crop residue. Research results conflict on this is-
sue with some showing significant pesticide loss reductions
from conservation tillage systems while others have observed
similar or even greater losses from conservation tillage
versus conventional tillage. The degree of rainfall inten-
sity appears to be the primary factor producing these
conflicting results.
The persistence of a given pesticide is critical to the
effectiveness of SWCPs in controlling its loss. Because
most. SWCPs function best for small to moderate size storm
events and are often overwhelmed by the most major storm
events, their long term effect is largely to retard the
movement of pesticides from field to aquatic system. Hence,
the degradation rate or soil leaching rate will greatly af-
fect surface runoff and groundwater loadings.
For weakly to moderately adsorbed pesticides which are
transported primarily in solution, there is generally an in-
herent trade-off between controlling surface runoff losses
and increasing leaching through the soil profile to ground-
waters. Management decisions to minimize overall
environmental impacts should consider the persistence of the
pesticide in relation to the rate of downward movement
through the soil, the relative importance of and potential
for use impairment by pesticides of neighboring surface and
groundwater resources, depth to the water table, and adsorp-
tive capacity of subsoils.
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TABLE 9
Effects of Soil and Water Conservation Practices
Effect on
Runoff Volume
Type of Practice
Structural Practices
Terraces
level
graded
Subsurface drainage 0
Sediment Ponds 0
Nonstructural Practices
Conservation Tillage
chisel plow -
ridge-plant -
no-till
Contouring
Stripcropping -
Grassed waterways 0
Diversions 0
Cover crops
Filter strips 0
Effect on
Soil Erosion
Effect on
Delivery
Ratio
0
0
0
0
0
*
0
1. "-" = Reduction, "+" = increase, "0" = Little or no effect.
"*" = Unknown, situation dependent or conflicting research results
Information taken from Maas et. al. (77).
3.2 PESTICIDE FORMULATIONS AND APPLICATION METHODS
,3.2.1 Formulations
As d5.scussed earlier under pesticide transport modes the
formulation can have a considerable effect on the loss by
various transport routes. Among the -most common formula-
tions for herbicides and insecticides are wettable powders,
dusts, concentrated emulsions, granules, liquid concen-
trates, soluble powders, aqueous solutions and flowable
solids. Although the appropriate formulation is often dic-
tated by the mode of action and the physical/chemical
properties of the pesticides, where a choice exists, the
following generalizations might aid selection:
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Wettable powders and micro granules are considered
the most susceptible for runoff losses (9);
Dusts, wettable powders and fine liquid sprays exhib-
it the greatest drift losses (30);
Aqueous solutions, liquids and liquid concentrates,
especially when applied as fine sprays, show the
greatest potential for volatile losses (17);
Formulations such as granules, pellets and emulsions
generally reduce volatile and drift losses (8).
3.2.2 Application Methods
As shown earlier in the review of transport mechanisms,
the application method can have a tremendous effect on pes-
ticide loss by all transport routes. Matthews (111) has
presented a detailed discussion of pesticide application
methods emphasizing advantages, disadvantages, and specifi-
cations. Table 10 shows some of the major application
options available for minimizing pesticide loss and indi-
cates which transport routes are most affected. Only direct
effects are included; i.e. an application technique which
increases efficiency of use and thereby allows a lower ap-
plication rate reduces the total amount of material
available for transport but may not affect the percentage of
applied material lost. For example, conversion from aerial
to ground spraying: The direct effect is a reduction in
drift losses, while the indirect effect might be that appli-
cation rate is reduced, thus decreasing runoff and volatile
losses.
3.2.2.1 Aerial Application
Indeed, as indicated earlier, the most effective single
management practice for reducing pesticide field losses may
be switching from aerial to ground application wherever pos-
sible. As noted by von Rumker et. al. (30) drift losses of
any pesticide will be substantial with aerial spraying. In
many eases, however, such conversion is not physically or
economically feasible. Large fields where rapid pest out-
breaks may occur or where application must be scheduled
around other field operations may necessitate aerial spray-
ing on the basis of timeliness. Crops which may require
application at advanced growth stages often preclude the use
of ground based equipment.
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TABLE 10
Options for Reducing Pesticide Application Losses
Option
Mechanical
ground vs. aerial
application 0
controlled droplet
applicators 0
computer controlled
equipment 0
drift shielded ground
sprayers 0
direct nozzles 0
ultra-low volume
(ULV) equipment
electrostatic sprayers 0
Physical
granules vs dust
formulations 0
oil emulsion
formulations -
ultralow volume
formulations
soil incorporated vs
surface application
optimal choice of
granular size 0
Management - timing
spraying only on
calm days 0
spraying late in day 0
using time release
formulations +
restrict application
before precipitation
night spraying 0
Effect on
Runoff Losses
Effect on
Drift Losses
Effect on
Volatilizatiol
Losses
0
0
0
0
0
"-" 3 Reduction, "+" = Increase,
= Little or no effect.
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For situations where a conversion to ground application
equipment is not practical, there are a variety of methods
for increasing the efficiency of aerial application. One of
the most important steps is to assure that the aircraft is
providing an even' distribution of pesticide to the target.
This procedure, known as swath analysis, has recently begun
using computer analysis of spray patterns to optimize the
settings of application nozzles for maximum efficiency (91).
Unlike ground-rig sprayers, uniform pesticide distribution
patterns result from very uneven placement of nozzles on the
spray boom because of air turbulence caused by the prop and
wings of the aircraft itself. An increase in application
efficiency of about 75% was observed for one test cited
(91). Hydraulic nozzles on aircraft produce smaller drops
than land machines because of the greater airspeed. This
problem can be compensated to some extent by facing the jets
backwards. The importance of highly even distribution be-
comes even more critical when using ultra-low volume
application (92). Other methods for minimizing losses from
aerial application include releasing pesticides as low above
the target as possible as well as timing and formulation
considerations. These latter include using granules, oil
emulsion, or larger droplets as opposed to dusts and fine
sprays and restricting applications to windless days when no
heavy precipitation is forecast.
3.2.2.2 Ground Application
The pesticide application machine (applicator) must sim-
iltaneously disperse and aim the application to an extent
that varies with mode of action, formulation and type of
crop. It has been noted that dispersal and aiming necessar-
ily conflict to some extent particularly when uniformity is
considered an aspect of aiming. Very fine particles dis-
perse better but their trajectory is more easily influenced
by air movement (93). Thus, in at least a conceptual sense,
all application equipment represents a compromise between
these two functions. Put another way, most equipment ad-
vances in recent times have centered on reducing drift while
still providing adequate and uniform dispersal. The mea-
surement of drift itself is subject to large experimental
error with the fall-out on sampling plates often poorly cor-
related with actual field and crop catchment (94).
Equipment which optimizes drop size can greatly reduce
drift losses. Recent developments in rotating-disc sprayers
have proven valuable for such controlled drop application.
Drops of 500 um or greater will produce little drift, and
except in extremely dry conditions, drop size can be reduced
to 100 or 200 um with minimal drift. As important as the
median drop size is the ability to produce drops within a
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narrow size range, reducing the output of small drops. One
recently developed machine reduces drift by transmitting the
spray horizonally at such a height that the horizontal com-
ponent of drop movement has ceased before the crop is
reached so that drops are falling vertically under calm con-
ditions (94). The importance of drop size is illustrated by
the work of Ware et. al. (95) who found that drift was twice
as large for a ground based mist blower applying 100 um
drops as from an aerial application with 140 um drops.
Equipment and formulations which use spray thickeners
have also been shown to reduce drift. These are usually wa-
ter-pesticide or oil-pesticide emulsions. The high
viscosity reduces small drop formation in the nozzle (93).
Oil emulsions can also reduce volatilization losses. Recent
studies with a controlled drop applicator using a soybean
oil carrier showed that with a median drop size of about 300
um. only 0.64 to 1.07% of the total volume was released as
droplets of less than 100 mm diameter (158). Electrostatic
sprayers have recently added a method for using small
(30-50u) easily dispersible drop sizes while minimizing
drift. A negative charge is added to the spray droplet by
a small electrode charging cap embedded near each nozzle
tip. The negatively charged drop is attached to the posi-
tively grounded plant (93f 96). Preliminary studies
indicate less drift and better foliar coverage for insecti-
cides than with conventional spraying equipment (96). A
variation of the electrostatic sprayer is the recirculating
sprayer in which droplets which are not deposited on plant
or soil surfaces are electrostatically recaptured by the
sprayer. Machinery costs are high at this time, however,
this innovation may prove very useful for ultra-low volume
application. At the present time ULV techniques are becom-
ing more popular because of reduced carrier expenses and
because more acreage can be treated with fewer refilling
stops (92): However, the potential for drift losses is cor-
respondingly increased by the small droplet sizes employed.
Wick applicators are a recent innovation for applying con-
tact herbicides with maximum efficiency. The
herbicide-saturated rope wick is drawn through the field
just above the level of the crop.
3.2.2."3 Management - Timing
Considerations for management decisions which can reduce
pesticide losses are shown in Table 10. These can be
grouped by the way they affect various pesticide transport
mechanisms.
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3.2.3 Reducing drift losses
As discussed previously the major factor influencing
drift losses are application method, pesticide formulation
and wind velocity. Investigations by several researchers
have shown wind velocity to be the most important factor af-
fecting drift losses (30, 8, 53) with drift loss ranging
from 0 to 50 percent depending on wind velocity. On this
basis the BMP for reducing drift is to restrict applications
to windless days or to periods of the day ( for example:
early morning, early evening or night) when wind velocity is
minimized. Spraying in windspeeds above 5 mi/hr should be
avoided in all cases. A recent statistically based study
has shown that night spraying would actually be the most ef-
fective means of minimizing both drift and volatilization
because of reduced windspeeds and evaporation potential
(112).
3.2.3.1 Reducing volatilization losses
Volatilization losses increase with pesticide volatility,
air temperature, soil temperature, and wind velocity and de-
crease in humidity. Losses of triazines and organochlorines
are particularly dependent on soil and air temperatures (20,
21, 23,152). Thus, it can be concluded that in terms of
timing decisions the BMPs for reducing volatile losses in-
volve applying pesticides on windless, humid and cool days
to the extent possible. Spraying should also be done late
in the day or at night to reduce volatile losses and in-
crease the time of contact between plant or insect and
pesticide. This is particularly important for pesticides
such as organophosphorus and organochlorine insecticides
where the half-life on foliage or soil may be on the order
of a few hours or less under hot, dry conditions (8).
3.2.3.2 Reducing runoff losses
For all the pesticide classes previously discussed in
Section II it is apparent that by far the greatest runoff
losses occur when a significant runoff event occurs shortly
after 'application. The shorter the interval between appli-
cation and runoff, the greater the pesticide runoff losses
(9). For this reason, in terms of application timing op-
tions, avoiding application when the probability of
significant precipitation is high is a BMP for reducing run-
off losses. Careful attention should be paid to local
weather forcasts in application decision making.
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-------
Chapter 4
INTEGRATED PEST MANAGEMENT (IPM) SYSTEMS
4.0.4 Basic Principles
Some of the individual non-chemical options for reducing
pesticide usage are shown in Table 11. These, together with
use of pesticides and the various application techniques,
form the basis of integrated pest'management. IPM has been
defined as an interdisciplinary approach to pest control in-
corporating the judicious application of ecological
principles, management techniques, and biological and chemi-
cal methods to maintain pest populations at tolerable levels
(98).
After several decades of almost exclusive reliance on
chemical strategies for controlling agricultural pests, IPM
has received wide support in recent years. This support has
increased because of the high cost of pesticides and a per-
ception that the negative effects of chemical pesticide
reliance have continued to magnify. These apparent negative
effects include increasing pest resistance which continually
reduce pesticide effectiveness; emergence of new pests due
to disruption of ecological controls; extensive contamina-
tion of water, air, and soils; widespread human health
hazards (over 40,000 reported cases of pesticide poisoning
in 1980) (98); and increasing pesticide costs. This growing
support for IPM is perhaps best exemplified by the 1979
Presidential .Directive, to .federal .agencies .to "modify as
soon as possible existing pest management/ research and con-
trol education programs to support and adopt IPM strategies"
(99). At the farm level many farmers receive most of their
information on pesticide selection and use from the local
distributor whose livelihood is tied to the quantity of pes-
ticides sold (6, 3, 101). Rapid progress has been made in
addressing obstacles to the adoption of a sound ecological
approach to pest control. An excellent summary of federal
and state actions in recent years to encourage IPM had been
published by Allen and Bath (100).
One of the basic tenants of IPM is that optimal pest con-
trol systems are highly situation-specific and depend on
extensive knowledge of the ecology of the system of inter-
est. Several excellent books have recently been published
which give detailed explanations of the IPM tools shown in
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TABLE 11
Major Components of Integrated Systems for Reducing
Pesticide Usage
a. more efficient application methods (see Table 10)
b. pesticide application based on economic thresholds
c. use of resistant crop strains
d. timing of field operations - planting, cultivating
harvesting
e. researching crop-pest ecosystem
f. scouting
g. use of biological controls
1) introduction of natural enemies
2) preservation of predator habitats
3) release of sterilized male insects
h. use of pheromones
1) for monitoring populations
2) for mass trapping
3) for disrupting mating behavior of pests
m. crop rotation
n. destruction of pest breeding, refuge and overwintering
sites
o. use of "trap" crops
p. habitat diversification
q. use of botanicals
Table 11. Among these are An Introduction to Integrated
Pest Management, Flint and van den Bosch (6); The least is
Best Pesticide Strategy, Goldstein (101); New Technology of
Pest Control, Huffaker (102); Plant Protection: An Integrat-
ed Interdisciplinary Approach, 'Sill (103); Integrated Pest
Management, Apple and Smith (109); and Integrated Pest Man-
agement: Rationale, Potential, Needs and Implementation,
Glass (104). The remainder of this section is devoted to
describing briefly some IPM concepts and to highlighting
some recent information which has been published subsequent
to the above-noted references. Case studies involving spe-
cific IPM systems will be included as part of major crop
pest control system discussions and recommendations in Sec-
tion IV.
Flint and van den Bosch (6) suggest the general guide-
lines for setting up IPM programs which are summarized
below.
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1. Understand the biology of the crop, and how .it: is^ in-
fluenced by the surrounding ecosystem. Important
considerations include the type of life cycle (annu-
al, biennial, perennial); growth initiation factors
(temperature, moisture, photoperiod); how the crop
plant responds to stress such as drought, nutrient
deficiencies and temperature; and how environmental
conditions affect growth rates and cycles.
2. Identify the key pests; know their biology; recognize
the kind of damage they inflict; and initiate studies
on their economic status. Key pests are organisms
which cause significant yield or quality reductions
regularly in the absence of pest management action
and usually there are only one or two key pests in a
given managed resource system.
3. Identify the key environmental factors that impinge
(favorably or unfavorably) upon pest and potential
pest species in the system. These are factors which
limit the survival, development and reproduction of
key pests and usually include natural enemies (para-
sites, predators and pathogens), availability of food
sources, temperatures, water availability, photoper-
iod, shelter and overwintering sites.
4. Consider concepts, methods and materials that indi-
vidually and in combination will help suppress
permanently or restrain pest species. Examples in-
clude introducing and establishing new natural
enemies to the system or permanently altering the
pests' physical environment to reduce reproduction
and/or survival.
5. Structure IPM programs so they will have the flexi-
bility needed to adjust to ecosystem changes.
Variations in pest situations may be observed between
neighboring fields and between years.
6. Anticipate unforseen developments; expect setbacks;
move with caution, and remain aware of the ecosystem
8,
complexity.
Seek the weak links in the
in the key
-i ~ , *"
jest life
rcle and
narrowly direct control practices at these weak links
avoiding broad ecosystem impacts. This includes ap-
plying control when the pest is more vulnerable with
tools that include pesticides or natural enemies.
Whenever possible use methods which preserve, comple-
ment and augment biotic and physical mortality
factors of the pest. Examples include providing sup-
plemental food sources for parasites and predators,
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adjusting planting times, and properly timing the use
of selective pesticides.
9. Whenever feasible, attempt to diversify the ecosys-
tem. Managed ecosystems have much less diversity in
terms of genetics, age, species and physical charac-
teristics than natural ecosystems. While this is
generally necessary for maximizing production effi-
ciency, it generally decreases the system's ability
to resist new stresses. Small changes to increase
diversity such as the addition of an alternative food
source shelter area, or pest host can make the dif-
ference between effective and ineffective pest
control (6, 102, 103).
4.0.5 Monitaring
Together, the above guidelines provide a strong conceptu-
al framework for how any IPM system should be designed. It
is clear from the above discussion that scouting and moni-
toring (surveillance) are perhaps the most important
ingredients of an IPM system. All decisions and actions for
pest control should be based on accurate timely information
on pest dynamics. Scouting or monitoring involves sample
collection in the field to determine pest levels and life
cycle stages. Among the sampling schemes used are random
sampling (4 or more counts of pest numbers and/or damage per
field); point sampling (detailed monitoring of pests, natu-
ral enemies and crop maturity in one area per field); traps
(light traps, sticky traps, pheromone attractant traps
(106)) which usually only determine pest presence rather
than density; and sequential sampling, a low cost method us-
ing economic thresholds to determine whether further
sampling is needed (6). It should be noted that economic
thresholds are a very "dynamic quantity which respond to fac-
tors both internal and external to the agroecosystem.
In practice, scouting or field monitoring for weeds have
proven easier than for insects because weeds are less tran-
sient. Two or three detailed scoutings and mappings per
season have generally been found to be sufficient (105).
4.0.6 Control Action Thresholds
The basic reason for determining thresholds is to differ-
entiate the mere presence or innocuous levels of a pest from
densities which will cause significant damage. In many cas-
es a crop can tolerate large numbers of insects or
considerable weed competition without significant yield
- 46 -
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losses. The principal of economic injury levels is based on
the concept that pest control is not justified until crop
injury reaches the level where the cost of control is less
than the cost the farmer would incur if control action were
not taken. Recent IPM models utilize this concept by deter-
mining optimal pest management systems on the basis of
profits to the producer rather than on maximization of
yields (130f131). In fact, most IPM studies have found that
maximum net returns are realized from management alterna-
tives which do not maximize crop yield but rather optimize
between pest-induced yield reductions and reductions in pes-
ticide costs (127,130,131,141).
As noted earlier, the interaction between the growth
stages of crop and pest species has a great effect on the
economic injury level of a crop. Most pests are able to
cause economic injury only during limited periods of the
plant or pest life cycle. An example is the tobacco budworm
which causes damage by feeding on tobacco leaf buds. How-
ever, by mid-summer all the leaves have emerged from their
buds so that the budworm regardless of density level cannot
cause economic damage for the remainder of the plants' life
cycle. Natural enemies also have an effect on economic in-
jury levels. Untreated cotton in California has an economic
threshold of 15 first or second instar bollworm larvae per
100 plants. In insecticide treated fields this threshold
drops to 8 larvae per 100 because of destruction of natural
bollworm enemies (6).
4.0.7 Biological Controls
1. natural enemies.
The role of natural enemies has already been men-
tioned. Control by natural enemies is generally
cheap, effective, permanent and nondisruptive, and
thus should be a paramount consideration in pest con-
trol strategies. Unfortunately, it is also the
factor most likely to be disrupted by the employment
of other control tactics particularly chemical pesti-
cide use.
2. host resistance.
This involves the genetic manipulation or selec-
tion of plant varieties which have pest resistant
qualities. Resistance may be due to physiological
factors (e.g. toxic compound produced by plant),
morphological factors (e.g. a cuticle which is too
thick for penetration by the pest) or increased tol-
erance in which case pests continue to feed on the
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host but damage remains below economic injury
thresholds.
autocidal control.
These are tactics which cause the pest to contrib-
ute to the reduction of its own population. The most
common tactic is to release sterile males which are
equally competitive with wild varieties thus reducing
reproduction success. Theoretically this technique
can reduce a given pest population almost to zero;
however this assumes that the release area is geo-
graphically isolated and that sterilized males are
easily reared and remain sexually competitive (6).
Such repetitive releases are also quite expensive.
4.0.8 Cultural Controls
Cultural controls are modifications of management prac-
tices that make the environment more unfavorable for
survival, movement and reproduction of pests. Cultural tac-
tics include timing of planting and harvesting, timing of
other field operations, field sanitation, tillage, trap
crops, cultivating, habitat diversification, and crop rota-
tion.
Crop planting can often be timed to give the crop a com-
petitive advantage over the pest. This has proven effective
for both insects and weeds. Harvesting practices such as
early harvest before occurrence of economically injurious
levels of pests which feed directly on the marketable por-
tion of the plant have proven effective for a wide variety
of pests including sugar cane borer, sweet potato weevil,
potato tuberworm and cabbage looper (6). Tillage practices
destroy both insect and weed pests by mechanical injury.
Trap crops have proven especially effective in cotton grow-
ing areas where a small portion of the field can be planted
in an early fruiting crop which attracts the majority of
pests. This area can then be sprayed with very high killing
efficiency while not impacting natural enemies in the rest
of the area. Crop rotation has long been shown to reduce
pest problems especially for pests which cannot survive over
one or" two seasons without host contact.
A majority of the IPM control tactics discussed in this
section have either implicitly or explicitly referred to in-
sect as opposed to weed control. The reason is that insect
control IPM programs have been under development longer and
have a considerably higher knowledge base than weed IPM pro-
grams which are still in their relative infancy. However,
several concepts, theories and techniques for non-chemical
- 48 -
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weed control systems are developing and deserve special
mention. Several of the IPM tactics discussed above are
used for weed control as well as insect control. These in-
clude tillage, crop rotations, and monitoring. In addition,
nonchemical weed control tactics have included mulching (on
intensively grown crops) and use of natural weed enemies
(parasites, pathogens, and especially insects) (107). Re-
cent work has focused on weed habitat modification
procedures that disturb weed growth or change competitive
patterns. Such measures include optimizing row spacings,
adjusting time of planting and fertilization patterns to
give the crop the maximum competitive advantage (105).
There is also extensive evidence that using weed-free seed
is a cost-effective BMP for weed control (107).
4.0.9 Evaluating IPM Programs
Evaluating the success of IPM has proven to be a diffi-
cult task. Pest problems vary widely on an annual basis as
a function of climatic and other environmental conditions.
This limits the reliability of 'before and after1 evalua-
tion. _ Even the traditional approach of comparing IPM
participants with non-program cooperators is of limited use
because of the farm to farm variation of pest dynamics and
the influence of adjacent pest control systems on each oth-
er. In several areas where long term comparisons have been
attempted the control group has become smaller with time, to
the point where all producers of a given commodity and geo-
graphic area have adopted some level of IPM (108). The
methodology being used by Boutwell and Smith (108) involves
the correlation of the percentage of recommended IPM tactics
being used by individual producers with their crop yields
and net returns.
Very little evaluation of IPM programs has been done in
regard to their effect on water quality. The assumption
generally made is that the reduction in field loss of pesti-
cides will be proportional to the reduction in application
rate. This assumption can be in error in either direction
depending on the pesticide, soil type and other field char-
acteristics.
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4.1 SUBSTITUTION OF MORE SELECTIVE OR LESS PERSISTENT
PESTICIDES
The fourth major group of techniques, substitution of
more selective/less persistent pesticides, also reduces
aquatic pollution by reducing the amount that can reach the
aquatic system. These may also augment the effects of the
preceding three groups of BMPs. SWCPs can increase the res-
idence times of certain pesticide classes on the field
before they are washed off to aquatic systems. Less persis-
tent pesticides sometimes have the agronomic disadvantage of
requiring more frequent application. If less persistent
pesticides are substituted, then SWCPs can be a more effec-
tive means of reducing pesticide runoff impacts on aquatic
systems. The same principal applies for reducing the impact
of drift and volatilization losses by modifying application
techniques. Although little is known about the atmospheric
residence time of volatilized pesticides, it is clear that
effective redeposition fluxes will be lower for more atmos-
pherically degradable materials. The use of highly
selective pesticides plays a vital role in the effectiveness
of IPM systems. Selective pesticides which minimize disrup-
tion of natural enemy dynamics ultimately increase the
efficiency of pest control on a long-term basis.
The greatest advance in the selectivity of pesticides has
come in the area of natural and synthetic pyrethroid devel-
opment. Natural pyrethroids represent the ideal insecticide
because of their selective action against a single insect
species, their lack of toxicity to humans, their rapid deg-
radation, their high efficacy (low application rates), and
their low potential for promoting resistance among pest
species. However, the identification, extraction and puri-
fication of biologically active pyrethroid isomers is very
costly and has only been accomplished for a few insect spec-
ies. Unfortunately, there is limited economic incentive for
research or development because the high selectivity limits
the market to a. single pest.
Synthetic pyrethroids basically are chemical analogs of
natural pyrethroids that work in the same manner as natural
pyrethroids. They are less expensive to produce; and in some
cases are effective on more than one group of related pests.
Synthetic pyrethroids have practically revolutionized insect
control in cotton, replacing toxaphene and organophosphorus
insecticides on the majority of insecticide treated cotton
acreage (63). In fact, the cotton acreage treated with tox-
aphene has declined by 81 percent since 1976. Synthetic
pyrethroid usage has also increased dramatically on soybe-
ans, and is now used more extensively than any other
insecticide on this crop. A recent USDA report indicated
that substitution of synthetic pyrethroids has resulted in a
significant decrease in overall U.S. insecticide demand
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(71). This is due to a combination of their low application
rates, infrequent need for application, and particularly be-
cause their light damage to beneficial insects and predators
reduces overall insecticide needs. One drawback from the
standpoint of water quality impacts is the fact that the
most commonly used synthetic pyrethroids are very highly
toxic to fish with 96hr LC(50) values in the low or sub
part-per billion range (113,153).
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Chapter 5
PESTICIDE BMP SYSTEMS BY CROP AND REGION
As noted earlier the most effective pest management
strategies for optimizing agricultural production and water
quality concerns are highly situation specific. In fact,
pest population and pesticide transport dynamics vary year
to year, farm to farm and even between fields. For this
reason flexibility must be built into any pest management
program to maximize effectiveness. With these concepts in
mind this section examines case studies of pest management
systems for major 'crops "and regions, and. attempts to inte-
grate these case studies with other information on pest
management practices for reducing water quality impacts.
The results are general guidelines for pest management in
major crops and areas with an added emphasis on the reduc-
tion of pesticide losses to aquatic systems. Some regions
of the U.S. have important economic crops which are not con-
sidered major crops on a national scale. BMP systems for
these locally important crops will also be mentioned where
information is available. Unfortunately, as will become ap-
parent in the following discussions, many BMP systems have
been designed for one class of pest (i.e. insects, weeds,
nematodes) without adequate consideration of the overall
system. This results in recommendations which do not take
into consideration other production necessities, or in the
worst cases, recommendations which conflict. In each exam-
ple an attempt is made to estimate the reductions in
pesticide inputs to aquatic systems possible for various
combinations of BMP systems relative to traditional produc-
tion practices.- In a few cases, these estimates are based
on quantitative research results. However, for most cases
these estimates are based at least partially on an intuitive
and conceptual consideration of the pesticide loss reduc-
tions possible through the combination of SWCPs, application
improvements and IPM.
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5.1
PESTICIDE BMPS FOR CORN
Corn is the largest single cash crop in the United
States. In 1982, almost 82 million acres were planted (63).
Of this acreage about 95 percent was treated with herbicides
and about 37 percent with insecticides. In spite of this
vast acreage and the large associated pesticide use, corn
has lagged behind several other major crops in the develop-
ment of biological and other nonchemical pest control
strategies. Both herbicide and insecticide treatments to
corn are generally made very early in the growing season
when the potential for erosion and runoff losses are great
due to the lack of vegetative cover and high precipitation
probability. In addition a larger percentage of corn is
grown on land classified as highly erosive by the 1977 Na-
tional Resources Inventory than any other crop except
tobacco (161). Hence, at a national level, the application
of SWCPs to corn acreage can make a significant contribution
to reducing impacts of .pesticides-on aquatic systems.
Most pesticide application to corn is made by ground-
based equipment and much of this material is in granular
form. Thus, the potential for reducing pesticide inputs to
aquatic systems through improvements in application tech-
niques Is less for corn than for some other major crops.
5.1.1 Insecticide Reduction through IPM
5.1.1.1 Scouting
Current insect control practices in corn are very depen-
dent on chemical insecticides, primarily carbofuran and
various organophosphorus compounds, with other controls usu-
ally subordinate. Replacement of prophylactic soil
treatments for .corn rootworms with better scouting programs
is one way that insecticide use can be reduced. It appears
that extensive treatment for corn rootworm takes place in
fields with little or no potential for rootworm damage. A
four-county Illinois study found that in 1974 and 1975, 19
and 11 percent respectively of corn acreage actually needed
insecticide treatment, while in fact, 67 and 57 percent re-
spectively were treated (115). A three-year study in the
Midwest showed that only 9 percent of corn fields even con-
tained wireworms, and only 1.2 percent actually had wireworm
damage (114). This illustrates the potential for reducing
corn insecticide use through the substitution of appropriate
scouting and monitoring accompanied by IPM education pro-
grams.
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5.1.1.2
Crop Rotation
It has been known for some time that the most effective
management practice for controlling corn insect pests is
crop rotation. The largest insect pests of corn are the
various species of corn rootworm. The corn rootworm is una-
ble to survive over a year when another crop is planted, and
thus corn rootworm populations are dramatically reduced by
rotations that skip corn on consecutive years. In the
short-term, the practice often suffers some economic disad-
vantage compared to rotations with successive corn planting.
However, in many cases alternating corn with some other an-
nual row crop such as soybeans, grain sorghums, forage
sorghams, or alfalfa at least partially and sometimes com-
pletely compensates for the loss of the corn rotation
because of reduced fertilizer applications, increased yields
during corn growing years and decreased insect problems.
For farmers heavily reliant on corn production on a majority
of fields, Luckman (115) proposes .a compromise which takes
advantage of both scouting and crop rotation. The concept
is to monitor corn fields at the end of the growing season
for rootworm beetle population. Fields with high infesta-
tion levels should be rotated to another crop the following
season while fields with lesser populations may be replanted
to corn the following spring. An extensive economic analy-
sis of corn cropping in the Midwest by Lazarus and Swanson
(154) produces a similar recommendation. Other non-chemical
management tactics for corn insect control involve adjusting
planting and harvesting dates to minimize damage or substi-
tution of of insect-resistant crop strains.
As presently practiced insecticide usage is only approxi-
mately 16 percent higher in no-till as compared with
conventionally tilled corn (78). This increase is reflected
in both higher application rates and increased acreage of
treatment. The increased insecticide requirement is a re-
sult of the lack of tillage to destroy or disrupt soil
insects and resistant weeds. The surface residue may also
result in cool, damp, early season soil conditions which in-
crease seedling susceptibility to insect damage (117).
Thus, crop rotation becomes even more important for insect
control in reduced-tillage systems. The effect of reduced
tillage on runoff losses of applied insecticides (carbofu-
ran, OPs) is unclear from the research conducted to date.
Table -12 summarizes the estimates of pesticide loss reduc-
tions from various BMPs and BMP combinations for corn.
These estimates are made at the field level as compared with
a hypothetical field utilizing conventional, traditional or
typical cropping practices realizing that these practices
may vary considerably between geographic regions.
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5.1.2 Possible Herbicide Reductions through IPM
IPM programs for weed control in corn are not well devel-
oped. ' Again, crop rotations somewhat reduce herbicide
requirements because some perennial weeds are more easily
controlled by competition or different herbicides in other
crops.
The growing use of no-till and other reduced tillage sys-
tems for corn has important implications for both herbicide
and insecticide application and loss. Although Hanthorn and
Duffy (78) have shown that herbicide usage is not signifi-
cantly greater for reduced tillage systems, the potential
for weed problems from the reduction in cultivation does not
lend optimism for significantly reducing herbicide usage in
reduced tillage systems (116). Furthermore, there is con-
flicting evidence on whether reduced tillage systems
actually reduce the percentage of applied herbicide lost in
runoff.
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TABLE 12
Estimates of Potential Reductions in Field Losses of
Pesticides for Corn Compared to a Conventionally and/or
Traditionally Cropped Field (1)
Management Practice
Transport Route(s)
Affected
Range of Pesticide
Loss Reduction
(Percent)(2)
SWCPs
Terracing
Contouring
No-till
Other Reduced
Tillage
Grassed Waterways
Sediment Basins
Filter Strips
Cover Crops
Optimal Application
Techniques (4)
Nonchemical
Methods
Adequate Monitoring
Crop Rotations
SR and/or SL(f)
SR and/or SL
SR and/or SL
SR and/or SL
SR and/or SL
SR
SR
SR
SR and/or SL
All Routes $
All Routes
All Routes
All Routes
40-75AB (25*)
15-55AB (20*)
-10 - +40B
60 - +10A (10*)
-10 - +60B
-40 - +20A (15*)
-10-20AB
0-10AB
0-10AB
0-20B(3)
10-20
20-40B
40-65A
40-70A
10-30B
* Refers to estimated i-ncreases--in* movement through soil
profile.
# SR = Surface Runoff
SL = Soil Leaching
$ Particularly drift and volatilization
1. The hypothetical field used as the basis for compari-
son utilizes the following management system: a)
Conventional tillage without other SWCPs. b) Ground
application with timing based only on field operation
convenience, c) Little or no pest monitoring; spray-
ing on prescribed schedule. d) Corn grown in 3 out
of 4 years.
2. Assumes field loss reductions are proportional to ap-
plication rate reductions. A = insecticides
(carbofuran and O.P.s) B = Herbicides (Triazine,
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Alachlor, Butylate, Paraquat) Ranges allow for varia-
tion in climate, slope, soils and types of pesticides
used. Ranges for No-till and Reduced-till are de-
rived from a combination of increased application
rates and decreased runoff losses.
Cover crops only will affect runoff and leaching
losses for pesticides persistent enough to be avail-
able over the non-growing season. In the case of
pesticides used on corn only the triazine and anilide
herbicides will generally meet this criteria.
Defined here for corn as ground application using op-
timal droplet or granular size ranges, with spraying
restricted to calm periods in late afternoon or eve-
ning.
5.2 PESTICIDE SMPS FOR SOYBEANS
Annual soybean acreage has increased steadily during the
past decade to where in 1982 it was only slightly less than
total corn acreage (81.9 million vs 72.2 million acres)
(63). Of the total acreage, 93 percent receives herbicide
treatment but only 12 percent is treated for insects. The
major herbicides used are metribuzin (triazine), trifluralin
(dinitroaniline) and alachlor. Primary insecticides are
carbaryl, various OPs, synthetic pyrethroids and toxaphene.
Definitive research has shown that all three of the above
herbicides are lost almost entirely in the dissolved phase
of runoff (8). Of the insecticides, only toxaphene is lost
primarily in the sediment bound phase. Thus, reductions in
herbicide losses should be roughly proportional to runoff
reductions for SWCPs, again with the exception of surface
residue effects that may result from reduced tillage.
Soybean pest problems vary considerably between regions.
The main soybean producing regions of the U.S. are the Corn
Belt, the South and the Southeast. Traditional production
has been confined to the Corn Belt and North Central regions
and at- the present time there are no major soybeans insect
pests in these regions (118). Much of the Corn Belt is also
relatively free of serious weed infestations although some
herbicidal control is needed on most fields (119). In the
Mid-South and Southeast, on the other hand, where production
acreage has increased dramatically in recent years, soybeans
are subject to attack by a large complex of insect pests
(120,121). Weeds are also a very difficult problem often
requiring multiple applications of both pre- and post-emer-
gence herbicides (122).
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5.2.1 Possible Reduction in Insecticide Use Through IPM.
The use of IPM systems for insect control in soybeans has
not been given much attention until recently as production
increased and expanded into new areas. However, several ex-
tensive studies have recently been conducted
(118,120,121,123,124). The largest effort has been the NSF/
EPA/USDA "Integrated Pest Management Project on the
Principles, Strategies, and Tactics of Pest Population Regu-
laton and Control in Major Crop Ecosystems" (123).
The most common IPM tactics for soybean include: 1) ade-
quate monitoring and scouting, 2) optimal planting dates, 3)
use of natural control agents, 4) Resistant varieties, 5)
trap crops, 6) selective use of insecticides, and
7)treatments based on economic injury levels.
In relation to economic injury levels, the soybean has a
remarkable ability to compensate for injury by insects with-
out loss of yield or quality (118). Hence, in its
traditional production regions, control by natural agents
has generally been sufficient.
In contrast to the Corn Belt, the new production regions
of the south-central and southeast U.S. have serious poten-
tial for insect pest problems as insects become adapted to
the new ecological niches available in soybean cropping.
The major challenge is to prevent the escalation of secon-
dary pests, the development of resistance and the loss of
natural predator controls, all of which are fostered by the
improper use of chemical insecticides (121).
In North Carolina and some other southeast states the
corn earworm, Heliothis zea, has historically been the major
soybean insect pest (120). Non-chemical control methods em-
phasize early planting so that a plant canopy is formed
before the flight of second generation moths. Related to
this are the use of narrow rows, plant varieties which form
an earlier canopy and other tactics to insure adequate crop
health. The earworm may be controlled by low rates of car-
baryl, based on larval populations to minimize disturbance
of natural biological control complexes.
The velvetbean caterpillar is the most important soybean
pest in Florida and Southern Texas. Wilkerson et. al. (124)
describe a spraying decision model based on insect scouting
information, crop growth stage, and economic threshold which
effectively minimizes the amount of pesticide application
for this pest.
In much of the rest of the South, various species of
stinkbugs are the major pests. Stinkbugs feed directly on
soybean pods and can cause considerable economic damage.
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The most effective non-chemical control technique has been
the use of trap crops, generally small areas (less than 5%
of the total), planted to varieties that mature one to two
weeks before the remainder of the crop. The early maturing
variety attracts the vast majority of stinkbugs as the pods
begin to fill and can be very efficiently sprayed with lit-
tle predator damage and minimal selective pressure (121).
5.2.2 Possible Reduction in Herbicide Use
Annual weeds, particularly giant foxtail, are the major
weed problem in the Corn Belt. These can be controlled to a
large extent by crop rotation (119). Extensive cultivation
is also considered a major factor in reducing herbicide re-
quirements on soybeans. Hanthorn and Duffy (78), however,
found that herbicide usage was not significantly greater for
most reduced tillage.--.systems-;, -than .for .conventional ..tillage
(Table 9). No-till systems used significantly more herbi-
cides only in the Midwest. Herbicide treatment in the Corn
Belt generally consists of using preplanting and pre-emer-
gence herbicides. No-till systems often require
post-emergence herbicides as well. Present efforts to re-
duce herbicide use focus on precise calculation of required
rates on the basis of soil organic content and pH as well as
using spot applications within fields (119).
Soybeans grown in the South-Central and Southeast regions
are subject to severe annual and perennial weed infestations
due to favorable climatic conditions (121). Post-emergence
as well as pre-plant and pre-emergence herbicides are often
required to maximize return. As in the Corn Belt, crop ro-
tation and precise application rates are BMPs. Early
planting, in addition to reducing corn earworm problems,
also reduces weed problems by providing an early crop cano-
py. It is clear that much more research on non-chemical
means of soybean weed control is needed in the South.
5.3 PESTICIDE BMPS FOR COTTON
Cotton has more proven potential than any other major
U.S. crop for achieving reductions in pesticide usage and
loss to aquatic systems through IPM, improved application
efficiency, and pesticide substitution. The percentage of
cotton acreage treated with herbicides rose from 82 to 97
percent between 1971 and 1982. However, actual amount of
herbicides used decreased by more than 10 percent during the
same period (63). A wide variety of herbicides are used,
but trifluralin and fluorometuron are the most predominant.
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f Insecticide use on cotton has been reduced substantially
since 1976. The percent of acreage treated with insecti-
cides has decreased from 60 to 36 percent in this period and
the amount by weight has dropped by almost three-fourths
(from 64.1 to 16.9 million pounds) (63). The majority of
this decrease can be attributed to the replacement of rou-
tine methylparathion and toxaphene treatment by IPM and
synthetic pyrethroids in addition to the adoption of early
maturing varieties to avoid late season pest problems.
Table 13 summarizes estimates of potential pesticide loss
reductions from various BMPs and BMP systems at a field lev-
el as compared with a hypothetical field utilizing cropping
practices which were typical until the late 1970s. The un-
certainty of the estimates-, is a function of the rapid
transitions in production method described above coupled
with the variance among regions and seasons. SWCPs in par-
ticular are not as effective on cotton as with corn and
soybeans because much cotton is grown on relatively flat
land with little or no water erosion problems (161).
Considerable potential exists in the case of cotton for
reducing aquatic pesticide inputs from drift because a high
percentage of treatment is made by aerial equipment.
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TABLE 13
Estimates of Potential Reductions in Field Losses of
Pesticides for Cotton Compared to a Conventionally and/or
Traditionally Cropped Field (1)
Transport Route(s)
Range of Pesticide
Loss Reduction
(Percent) (2)
SWCPs
Terracing
Contouring
Reduced Tillage
Grassed Waterways
Sediment Basins
Filter Strips
Cover Crops
Optimal Application
Techniques (3)
Nonchemical
Methods
Scouting Economic
Thresholds
Crop Rotations
Pest Resistant Varieties
Alternative Pesticides
SR and SL#
SR and SL
SR and SL
SR and SL
SR
SR
.SR and SL
All Routes($)
All Routes
All Routes
All Routes
All Routes
All Routes
0-(20*)
0-(20*)
-40 - +20 AB
0-10AB
0-10AB
0-10AB
0-10A
-20 - +10B
40-80A
30-60B
40-65A
0-30B
0-20A
10-30B
0-60A
0-30B
60-95A
0-20B
* Refers to estimated increases in movement through soil profile,
# SR = Surface Runoff
SL = Soil Leaching
$ Particularly drift and volatilization
1. The hypothetical traditionally cropped comparison field
utilizes the following management system:
a) Conventional tillage without other SWCPs.
b) Aerial application of all pesticide with timing based
only on field operation convenience.
c) Ten insecticide treatments annually with a
total application of 12 kg/ha based on
prescribed schedule.
d) Cotton grown in 3 out of 4 years.
e) Long season cotton varieties.
2. Assumes field loss reductions are proportional
to application rate reductions.
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3.
A = insecticide (toxaphene, methylparathion,
synthetic pyrethroids).
B = Herbicides (trifluralin, fluometron).
Ranges allow for variation in production region,
climate, slope and soils.
Defined for cotton as ground application using
optimal droplet or granular size ranges with
spraying restricted to calm periods in late
afternoon or at night when precipitation is not
imminent.
5.3.1 Potential Insecticide Reductions Through IPM
It is widely recognized that further reductions in insec-
ticide use on cotton will occur as IPM programs expand and
their combined effects stabilize and reduce the pest status
of various species. This should also lessen selective pres-
sures towards producing insecticide-resistance in pest
species (127).
A number of studies on the substitution of IPM and syn-
thetic pyrethroids for the hazardous and persistent
toxaphene suggest that this pesticide can be eliminated from
cotton production systems entirely (8, 127, 128). As a re-
sult of the cotton IPM effort spearheaded by the
NSF/EPA/USDA IPM project, functional integrated systems have
been developed for all major cotton producing regions of the
U.S. In Arkansas, implementation of the suggested IPM sys-
tem resulted in an 80 percent reduction in the number of
sprayings for the bollworm (129). California IPM projects
through emphasis on scouting and economic thresholds have
dramatically reduced insecticide needs in this important
production region without reducing -yields or profits
(128,130). IPM efforts in Texas have emphasized using short
season cotton to eliminate late season insect problems and
reducing spraying for flea hoppers (127,129,131). In a Mis-
sissippi study insecticide costs were cut in half simply by
using a cotton crop model to key insecticide treatments to
economic thresholds (128).
It 'is currently very difficult to assess what further re-
ductions in cotton insecticide use are presently feasible
because of the rapid transition presently underway. The
current trend in cotton production involves pesticide sub-
stitution by materials that require lower application rates
and have less adverse effect on natural control agents, a
reduction in aerial spraying, and use of pest resistant crop
varieties. However, given the short time during which these
advances have been under development, further developments
are nearly certain.
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5.3.2 Potential Herbicide Reductions
Almost no attention has been given to weed IPM systems
for cotton in the published literature. The focus of con-
cern has understandably been on developing insect IPM
programs. The heaviest cotton herbicide use is in the Mid-
South growing region where hot, humid weather contributes to
prolific weed growth. Reductions in herbicide use have come
about primarily through improved application efficiency,
more effective herbicides, crop rotation (primarily with
soybean (115)), and increased scouting activity. Additional
improvements in these have the potential to somewhat further
reduce herbicide usage without adversely affecting economic
returns.
5.4
TOBACCO
Herbicides and insecticide use has steadily increased
over the past decade on tobacco lands. Treatment reached 71
percent (herbicides) and 85 percent (insecticides) of total
acreage in 1982 (63). The tobacco IPM program for North
Carolina developed by Rabb et. al. (132) addresses the two
major N.C. tobacco insect pests, The tobacco budworm and the
tobacco hornworm; nematodes, particularly the root knot nem-
atodes; and the three common plant pathogens, tobacco mosaic
virus, bacterial wilt and "black shank", a fungal disease.
Four natural predators, the stilt bug, paper wasps, a
parasitic wasp and a parasitic tachnid fly have proven ef-
fective for control of the hornworm and budworm such that
there is
only occasional need for an insecticide application. Cul-
tural controls for nematodes and pathogens include crop
rotation and use of resistant varieties. Field sanitation
including rapid post-harvest removal of crop stubble is es-
pecially important for control of all three pest classes.
This is one area where considerable improvement is still
needed although post harvest sanitation has become standard
recommended practice. Significant reductions in insecti-
cide, nematocides and multipurpose pathogen. control
chemicals should be possible as these systems are used more
widely in tobacco production.
Tobacco lands are very significant from a water quality
perspective. The sensitivity of the crop to excess soil
moisture means that surface drainage systems are generally
required which increases the delivery ratio of applied pes-
ticides to nearby aquatic systems. Also, a large percentage
of tobacco lands are classified as highly erosive. Hence,
tobacco acreage represents a small but potentially intense
pesticide source.
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5.5 DECIDUOUS TREE FRUITS
The major deciduous tree fruits in the U.S. include ap-
ples, peaches, pears, cherries, and plums. Of these, apples
are by far the largest and most widespread crop and have re-
ceived the most attention in IPM program development.
Nearly 12 million pounds of pesticides were used on ap-
ples in the U.S. in 1978 (98) ranking this crop in the top
six in pesticide use. Of this amount over 7 million pounds
were fungicides. Research efforts (133,134,135,136) in sev-
eral areas of the country have developed IPM technology for
apples and other deciduous tree fruits which should reduce
pesticide use by 50 to 80 percent, depending on region and
the current level of IPM practiced. Excessive and often un-
necessary state and federal "cosmetic" standards for grading
and marketing fruit continue to pose a major barrier to the
adoption of IPM and subsequent pesticide use reduction
(6,137).
5.6 OTHER CROPS WITH HIGH PESTICIDE USAGE
IPM programs have been developed or are under development
for many other crops of national or regional significance
including alfalfa, potatoes, citrus and peanuts. Implemen-
tation of these programs can complement the potential
pesticide reductions described thus far. Regionally, these
may be of even greater importance since they may represent
the major crop and source of pesticide contamination for a
region.
An example is the development of IPM programs for pota-
toes which are a dominant crop in areas of Maine, Colorado,
and Idaho. Research in each of these areas (138,139,140)
shows that fungus- and -insect problems and the associated
need for chemical treatment can be reduced substantially by
IPM programs which employ antagonistic fungal species (135),
blight and insect resistant cultivars, crop rotations, dis-
ease-free seed, and soil pH manipulation (139). In Colorado
the use of a tachnid fly as a predator on the potato beetle
has been shown to have potential to greatly reduce use of
the insecticide aldicarb (140).
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5.7 SUMMARY OF PESTICIDE BMPS FOR MAJOR CROPS
1. Corn
The greatest potential for reduction in pesticide
losses from this crop involves reducing insecticide
use. The major BMPs for accomplishing this include
crop rotation to maintain insect pest populations at
low levels, and adequate field monitoring so that
pesticide applications are not made to fields which
do not have pest problems. Crop rotation will also
reduce herbicide needs to some extent. SWCPs have
potential for significantly reducing pesticide losses
from corn cropping because of the types of pesticides
used and the fact that two-thirds of this crop is
grown on moderately to highly erosive land (161).
Improvements in pesticide application technique can
reduce losses somewhat, but the potential is less
than for some other .major crops. Gross .pesticide in-
puts to aquatic systems from this crop can be reduced
between 60 and 80 percent using current technology.
2. Soybeans
The greatest challenge . relating to insecticide
contamination from soybean cropping is to prevent the
emergence of new pest complexes as soybean production
continues to spread into the South-east and South-
central U.S. This can be accomplished by
well-researched IPM programs. Reducing herbicide us-
age is accomplished most effectively by crop
rotation, early planting, and precise application
rates. Much more research on controlling soybean
weed pests is needed.
An increasing amount of soybean acreage, especial-
ly in the south-central U.S., is being aerially
sprayed, indicating potential for reducing field
losses through application method improvements.
SWCPs have some potential to augment pesticide loss
reductions from IPM and improvements in application
methods. Overall pesticide use and subsequent losses
to aquatic systems are in danger of increasing over
current levels. However, using current knowledge and
anticipated advances in weed IPM, reductions in pes-
ticide inputs to surface waters of 20-40 percent
should be attainable.
3. Cotton
Dramatic reductions have been made in cotton in-
secticide usage through IPM programs. Further
reductions are feasible through expanded IPM imple-
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mentation. Significant reductions in drift and
volatilization losses of pesticides can be accom-
plished most effectively by improvements in
application method and timing. Weed IPM programs for
cotton are still largely undeveloped. Herbicide use
reductions at the present time are most effectively
accomplished by crop rotation and precise application
rate.
SWCPs have very limited potential compared to IPM
and application improvements for reducing pesticide
runoff losses because a majority of cotton is grown
on fields with little slope and low erosion rates.
Pesticide pollution of groundwater aquifers is the
major water resource impairment in many cotton-grow-
ing areas; runoff-reducing SWCPs may exacerbate this
problem depending on soil type, pesticide mobility,
and depth to groundwater. Further overall reductions
in pesticide use and field loss in the range of 50 to
75 percent are possible with current IPM and applica-
tion technology.
4. Tobacco
Tobacco lands represent potentially intense sourc-
es of aquatic pesticide contamination because of the
combination of intensive pesticide usage and the need
for extensive surface drainage. Reducing pesticide
use through expanded implementation of IPM programs
appears to be the most effective and agronomically
practical means of reducing pesticide inputs from
this source. Overall reductions in pesticide inputs
to aquatic systems should be almost directly propor-
tional to reductions in application rates, estimated
to be in the range of 40 to 60 percent with current
knowledge and present economics of tobacco produc-
tion.
5. Decidious Tree Fruits
Reduction in pesticide aquatic inputs (primarily
fungicides) of 50 to 80 percent are attainable prima-
rily through IPM.
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Chapter 6
CONCLUSIONS
In some cases, there may be inherent tradeoffs be-
tween controlling pesticide loss and other
agricultural pollutants. An example is no-tillage
systems which reduce sediment losses but increase
pesticide use and subsequent losses of volatile, and
in some cases, runoff-carried pesticides.
For weakly to moderately bound pesticide types, man-
agement- practices which reduce losses from surface
runoff, drift or volatilization may increase the po-
tential for groundwater contamination depending on
soil type, topography and depth to water table.
Volatilization and drift with subsequent deposition
appear to be the largest pathways by which pesticides
reach aquatic systems. However, this input is dif-
fuse relative to surface runoff leaving the relative
importance unclear in terms of aquatic system im-
pacts .
Even in cases where eliminating aerial application of
pesticides is not feasible, options exist for improv-
ing the efficacy of such application methods; most
notably, swath analysis, and timing based on meteoro-
logical conditions.
IPM and improved-application efficiencies appear to
be more effective than SWCPs in reducing pesticide
inputs to aquatic systems. In some situations, how-
ever, such as on steeply sloping cropland directly
adjacent to water courses, SWCPs will be the most ef-
fective means of reducing aquatic impacts.
Management techniques, such as avoiding runoff-prone
formulations (wettable powders, microgranules) and
restricting application when storm events are antici-
pated, may be more cost effective than SWCPs for
controlling runoff losses of pesticides.
Losses of pesticides which are transported almost en-
tirely in the sediment phase of runoff, such as
toxaphene, other organochlorines, and paraquat can be
reduced by sediment control BMPs. However, the ex-
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tent of reduction is somewhat less than the sediment
reduction because of the disproportionate amounts ad-
sorbed on small sediment particles which are less
controlled by sediment control BMPs.
8. Recent pest control trends indicate that the most
cost effective method of reducing environmental im-
pacts of toxaphene is the substitution of synthetic
pyrethroids, especially on cotton.
9. For pesticides such as the carbamates, organophosp-
hates, triazines and anilides which are lost
primarily in the dissolved phase of runoff, losses to
surface waters will be decreased by the use of run-
off-reducing practices including terraces,
contouring, and in some cases, reduced tillage.
10. Conservation tillage systems as runoff-reducing prac-
tices do ,not always result in reduction of pesticide
losses in runoff. The decrease in runoff volume is
at least partially, and in some cases completely,
negated by the increased availability of pesticides
on surface residue. If the first runoff event after
application is very large, greater losses are usually
observed from conservation tillage systems; if the
first event is small, conservation tillage systems
usually exhibit much lower pesticide losses than con-
ventional systems.
11. In terms of gross amounts, application efficiency im-
provements can probably reduce pesticide field losses
more than SWCPs or IPM. However, drift and volatili-
zation losses are generally more diffuse, and further
research is-needed to evaluate their relative signif-
icance to aquatic systems.
12. The potential of- I-PM programs to reduce chemical pes-
ticide usage and subsequent loss to the surrounding
environment- continues to be great. Use reduction po-
tential based on current and developing technology,
however, varies greatly with crop. Tremendous reduc-
tion are feasible for corn and deciduous fruits,
while only moderate reductions can be expected for
soybeans.
13. Cotton pesticide use has fallen 75-80% since 1976.
Further reductions are anticipated but will be less
dramatic.
14. The trend of increasing use of ultra-low-volume (ULV)
pesticide formulations should be discouraged as these
formulations contribute to an increase in drift loss-
es of pesticides.
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15. From the viewpoint of minimizing environmental losses
of pesticides aerial spraying is uniformly undesira-
ble, and alternative methods should be used whenever
possible.
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*U.S. Government Printing Office: 1992648-003/40764
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