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.
                          -  111  -

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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
                           - v

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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).
                          - vi -

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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
                          -  vn  -

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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
                      - vin -

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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%.
                   - ix -

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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

                          - xi -

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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
                            xn -

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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
                         - xni -

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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;
                           -  1  -

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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
                           - 3 -

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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

-------
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 —

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                           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 -

-------
   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  -

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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 -

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                           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 -

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 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 -

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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 -

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 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 -

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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  -

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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 -

-------
 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.

                           -  26  -

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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.
                          - 28 -

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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
                          - 34 -

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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.
                          - 35 -

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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:
                           -  36  -

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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.
                          - 37 -

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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.
                          - 38 -

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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
                          - 39 -

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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
                          - 43 -

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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.
                           -  44 -

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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,
                       - 45 -

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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
                          - 47 -

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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.
                          - 49 -

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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
                          -  50 -

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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).
                          -  51  -

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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.
                          - 53 -

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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.
                          - 54 -

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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.
                          - 55 -

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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.
                           - 56 -

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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,
                          - 57 -

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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).
                           - 58  -

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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.
                          - 59 -

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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.
                           -  60  -

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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.
                          - 61  -

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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.
                           - 62 -

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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.

                          -  63 -

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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.
                          - 64 -

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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).
                          - 65 -

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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-
                          - 66 -

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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.
                       - 67 -

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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-
                   - 69 -

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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.
                       - 70 -

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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.
                       - 71 -

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                      REFERENCES CITED
1.   Huffaker, C. B. and R. F. Smith.  1980.  "Rationale,
     Organization, and Development of a National Integrated
     Pest Management Project."  pp. 1-25.  In: New
     Technology of Pest Control.  C. B. Huffaker ed. John
     Wiley and Sons.  500 p.

2.   Carson, R. A.  1962. "Silent Spring."

3.   Flint, M. L. and R. van den Bosch.  1981.
     "Introduction to Integrated Pest Management."  Plenum
     Press, N.Y. 	240 p.

4.   Valencia, R. M.  "Mutagenesis Screening of Pesticides
     Using Drosoplila."  EPA Report.  EPA 600/51-81-017,
     PB81-160848.

5.   Environmental Protection Agency.  1978.  "Fish Kills
     Caused by Pollution, Fifteen - Year Summary."
     1961-1975.

6.   Van den Bosch, R. 1978. "The Pesticide Conspiracy."

7.   Leonard, R. A., Bailey, G. W. and R.R. Swank Jr.  1976.
     "Transport, Detoxification, Fate and Effect of
     Pesticides in Soil and Water Environments."  Land
     Application of Waste Materials.  Soil Conservation
     Society of America.  Ankeny, Iowa. pp. 48-79.

8.   Shoemaker, C.- A.- and -M. O. Harris. 1979. "The
     Effectiveness of SWCPs in Comparison with Other Methods
     for Reducing Pesticide Pollution.  In:  Effectiveness
     of Soil and Water Conservation Practices for Pollution
     Control."  Haith, D. A. and R. C. Loehr. Eds.
     EPA-600/3-79-106.  pp. 206-234.

9.   Wauchope, R. D. 1978. "The Pesticide Content of Surface
     Water Draining from Agricultural Fields.  A Review."
     Journal of Environmental Quality.  7(4). pp. 459-472.

10.  Anderson, L. W. D. 1981.  "Control of Aquatic Weeds
     with Hexazimone."  Journal of Aquatic Plant Management
     19:9-14.

11.  Plumley, F. G. and D. E. Davis. 1980.  Estuaries
     3(4):271-277.
                          - 73 -

-------
12.  Boyle, T. P. 1980.  "Effects of the Aquatic Herbicide
     2,4-D DMA on the Ecology of Experimental Ponds."
     Environmental Pollution (Series A) 21(1):35-49.

13.  Brower, W. 1980. "Biological and Physical
     Investigations of Bodies of Water Beneath Dense Water
     Hyacinth Populations"Before and After Chemical
     Treatment." University of Florida Ph.D. Thesis. 277 p.

14.  Jones, R. D. and M. A. Hood. 1980. "The Effects of
     Organophosphorus Pesticides on Estuarine Canadian
     Journal of Microbiology 26(11):1296-1299.

15.  Lichtenstein, E. P., Schultz, K. R. and T. W.
     Puhreman. 1971. "Effects of a Cover Crop Verses Soil
     Cultivation on the Fate and Critical Distribution of
     Insecticide Residues in Soil 7 to 11 Years After Soil
     Treatment."'  Pesticides Monitoring Journal
     5(2):761-765.

16.  Ware, G. W., Cahill, W. P., Gerhardt, P. D. and K. R.
     Frost. 1970. "Pesticide Drift IV: On-Target Deposits
     from Aerial Application of Insecticides."  Journal of
     Economic Entomology 63(4):1982-1985.

17.  Willis, G. H., McDowell, L. L. , Smith, S., Southwick,
     L. M. and E. R. Lemm.  1980.  "Toxaphene Volatilization
     from a Mature Cotton Canopy."  Agronomy Journal
     72:627-631.

18.  Farmer, W. J., Igue, K., Spencer, W. F. and J. P.
     Martin.  1972. "Volatility of Organochlorine
     Insecticides from Soil:  I.  Effect of Concentration,
     Temperature, Airflow Rate and Vapor Pressure."  Soil
     Science Society of America Proceedings 36:443-447.

19.  Guengi, W.TD.-and W. E. Beard. 1974. "Volatilization of •
     Pesticides."  In:  W.  D. Guengi (ed.) Pesticides in
     Soil and Water.  Soil Science Society of America Inc.
     p. 107-122.

20.  Nash, R. G., Beall, M. L.  Jr. and W. G. Harris. 1977.
     "Toxaphene and l,l,l,-trichloro-2,2-bis(p-chlorophenyl)
     Ethane (DDT) Losses from Cotton in an Agroecosystem
     Chamber."  Journal Agricultural and Food Chemistry
     25(2):336-341.

21.  Hague, R. and V. H. Freed. 1974. "Behavior of
     Pesticides in the Environment: Environmental
     Chemodynamics."  Residue Reviews 52:89-116.
                          - 74 -

-------
22.  Willis, G. H., McDowell, L. L. and L. D. Meyer. 1979.
     "Toxaphene Washoff from Cotton Plants by Simulated
     Rainfall."  ASAE Paper No. 79-2507.  St. Joseph,
     Michigan.

23.  Swoboda, A., Thomas, G. W., Cady, F. B., Baird, R. W.
     and W. G. Knisel. 1971.  "Distribution of DDT and
     Toxaphene in Houston'Black Clay on Three Watersheds."
     Environmental Science and Technology. 5(2):141-145.

24.  La Fleur, K. S., Wojeck, G. A. and W. R. McCaskill.
     1973.  "Movement of Toxaphene and Fluometuron through
     Dunbar Soil to Underlying Groundwater."  Journal of
     Environmental Quality 2(4):515-518.

25.  Willis, G. H., McDowell, L. D., Parr, I. F.   and C. E.
     Murphree. 1976.  "Pesticide Concentrations and Yields
     in Runoff and Sediment from a Mississippi Delta
     Watershed."  Proc. --Third. Federal. Interagency
     Sedimentation Conference, Denver, Colorado.

26.  Sanborn, J. R., Metcalf, R. L., Bruce, W. H.  and P. Y,
     Lu. 1976.  "The Fate of Chlordane and Toxaphene in a
     Terrestial-Aquatic Model Ecosystem."  Environmental
     Entomology 5(3) : 533-538.

27.  Sanborn, J. R., Francis, B. M., and R. L. Metcalf.
     1977.  "The Degradation of Selected Pesticides in Soil:
     Review of the Published Literature."  EPA-9-77-022.
     U.S. Environmental Protection Agency. Washington, D.C.

28.  Eichelburger, J. W.  and J. J. Lichtenberg. 1971.
     "Persistence of Pesticides in River Water."
     Environmental Science and Technology 5:541-544.

29.  Adair, H. M., Harris, F. A., Kennedy, M. V.   Laster, M.
     L. and F. D. Threadgi'll. 1971.  "Drift of Methyl
     Parathion Aerially Applied Low Volume and Ultra Low
     Volume."  Journal of Economic Entomology 64(3):718-721.

30.  von Rumker, R., Kelso, G. K. Horay, F. and K. A.
     Lawrence. 1975.  "A Study of the Efficiency  of the Use
     of Pesticides in Agriculture."  EPA-9/75-025. U.S.
     Environmental Protection Agency, Washington, D.C.

31.  Spencer, W. F., Farmer, W. J. and M. N. Cliath.  1973.
     "Pesticide Volatilization."  Residue Reviews 49:1-47.

32.  Spencer, W. F., Shoup, T. D., Cliath, M. M., Farmer, W.
     J., and R. Hague.  1979. "Vapor Pressure and Relative
     Volatilitity of Ethyl and Methyl Parathion."  Journal
     of Agricultural Food Chemistry 27:273.
                          - 75 -

-------
33.  Spencer, W. F. and M. M. Cliath. 1973. "Pesticide
     Volatilization as Related to Water Loss from Soil."
     Journal of Environmental Quality.  284 pp.  27s273.

34.  Quinbyf G. E., Walker, K. C. and W. F. Durham. 1958.
     "Public Health Hazards Involved in the Use of Organic
     Phosphorus Insecticide in Cotton Culture in the Delta
     Area of Mississippi."  Journal of Economic Entomology
     51x831-838.

35.  Mulla, M. S., Mian, L. S. and J. A. Kawecki.  1981.
     "Distribution Transport and Fate of the Insecticides
     Malathion and Parathian in the Environment." Residue
     Reviews 81:1-72.

36.  Gunther, F. A., Iwatar, Y., Carman, G. F. and C. A.
     Smith. 1977. "The Citrus Reentry Problem:  Research on
     its Causes and Effects, and Approaches to its
     Minimization.'.1 -Residue Reviews 67:pl.

37.  Arthur, R. D., Cain, J. D. and B. F. Barrentine.  1976.
     "Atmosphere Levels of Pesticides in the Mississippi
     Delta."  Bulletin of Environmental Contamination and
     Toxicology 15(2):129-134.

38.  Miles, J. R. and C. R. Harris. 1978.  "Insecticide
     Residue in Water Sediment and Fish of the Drainage
     System of the Holland Marsh, Ontario, Canada,
     1972-1975." Journal of Economic Entomology 71:p. 125.

39.  Nicholson, H. P., Webb, H. J., Laver, G.  J., O'Brien,
     R. E., Grzenda, A. R. and D. W. Shanklin. 1962.  and
     Duration."  Transactions of the American Fisheries
     Society 91:213-217.

40.  Harris, C. R. and J. R. W. Miles. 1975.  "Pesticide
     Residues in- the Great-Lakes Region of Canada." Residue
     Reviews 57:27-34.

41.  King, P. H. and P. L. McCarty. 1968.  "A
     Chromatographic Model for Predicting Pesticide
     Migration in Soils." Soil Science 106.  p. 248-268.

42.  Karr, J. R. and I. S. Schlosser. 1977.  "Impact of
     Nearstream Vegetation and Stream Morphology on Water
     Quality and Stream Biota."  EPA-600/3-77-097.

43.  Caro, J. H., Freeman, H. P. and B. C. Turner.  1974.
     "Persistence in Soil and Losses in Runoff of Soil-
     Incorporated Carbaryl in a Small Watershed."  Journal
     of Agricultural Food Chemistry 22:860-863.
                          - 76 -

-------
44.  Caro, J. H., Freeman, H. P., Glotfelty, D. W., Turner,
     B. J. and W. M. Edwards. 1973. "Dissipation of Soil-
     Incorporated Carbofuran in the Field."  Journal of
     Agricultural Food Chemistry 21:1010-1015.

45.  Smith, E. G., Whitaker, F. D. and H. G. Heinemann.
     1976.  "Losses of Fertilizers and Pesticides from
     Claypan Soils."  EPA 660/2-74-068. U.S. Environmental
     Protection Agency.  Athens, Georgia.

46.  Stewart, B. A., Woolhiser, D. A., Wischmeier, W. H.,
     Caro, J. H. and M. H. Frere. 1975. "Control of Water
     Pollution from Cropland." Vol. 1. EPA-600/2-75-026a.
     U.S. Environmental Protection Agency.  Washington, DC.

47.  yon Rumker, R., Lawless, E. W., Meiners, A. F. 1974.
     "Production, Distribution, Use and Environmental Impact
     Potential of Selected Pesticides."  EPA-1/74-001, U. S.
     Environmental Protection. Agency, Washington, D.C.

48.  Mather, S. P., Hamilton, H. A., Greenhalgh, R.,
     MacMillian, K. A. and S. U. Khan. 1976. "Effect of
     Microorganisms on Persistence of Field Applied
     Carofuran and Dyfonate in a Humic Mesisol."  Canadian
     Journal of Soil Science 56:89-96.

49.  Bailey, G. W., Barnett, A. P., Payne, W. R. and C. N.
     Smith.  1974. "Herbicide Runoff from Four Coastal Plain
     Soil Types."  EPA-660/2-74-017. U. S. Environmental
     Protection Agency.  Washington, D. C.

50.  Paulson, D. 1981. "Effect of pH, Organic Matter and
     Soil Texture on Herbicides." Solutions, p. 40-54.

51.  Ritter, W. F., Johnson, H. P., Lovely, W. G. and M.
     Molnau.  1974. "Atrazine, Propachlor, and Diazinon
     Residues on Small Agricultural Watersheds: Runoff
     Losses, Persistance and Movement." Environmental
     Science and Technology 8(1):38-42.

52.  Triplett, G.  B.,  Conner, B. J. and W. M. Edwards. 1978.
     "Transport of Atrazine and Simazine in Runoff from
     Conventional and No-Tillage Corn." Journal of
     Environmental Quality 7(l):77-84.

53.  Baker, J. L.  and H. P. Johnson. 1977. "Tillage System
     Effects on Runoff Water Quality:  Pesticides."  ASAE
     Paper No. 77-2594B. American Society of Agricultural
     Engineers, St. Joseph, Mich.

54.  Hall/ J. K. 1974. "Erosional losses of s-Triazine
     Herbicides."   Journal of Environmental Quality
     3(2):174-180.
                          - 77 -

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 55.  Baker, J. L.,  Johnson, H.  P. and J. M. Laflen. 1976.
     "Completion Report:  Effect of Tillage Systems on Runoff
     Losses of Pesticides: A  Simulated Rainfall Study."
     Transactions of  the  ASAE 21:886-892.

 56.  Harvey, R. G., Peterson,  A. E., Higgs, R. L. and H. W.
     Paulson. 1976.   "Influence of Tillage and Planting
     Practice on Erosion  and  Atrazine Runoff."  Weed Science
     Society of America Abstracts, p. 5.

 57.  Smith, G. E., Whitaker,  F. D. and H. G. Heineman.
     1974. "Lossses of Fertilizers and Pesticides from
     Claypan Soil. Environmental Protection Technology
     Series." EPA-660/2-74-068.

 58.  deNoyelles, F. and D. Kettle. 1980. "Herbicides in
     Kansas Waters -  Evaluations of the Effects of
     Agricultural Runoff  and  Aquatic Weed Control on Aquatic
     Food Chains."  -Kansas Water Resources Research
     Institute Report No. 219.  48 p.

 59.  Richard, J., G.  Junk, M. Avery, N. Nehring, J. Fritz
     and H. Suec. 1975. "Analysis of Various Iowa Waters for
     Selected Pesticides: Atrazine, DDT and Dieldrin -
     1974."  Pesticides Monitoring Journal 9(3):117-123.

 60.  Gerhart, J. 1983. U.S. Geological Survey, Harrisburg,
     PA.  "Personal Communication."

 61.  Liu, L. C. and H. R. Cibes-Viade. 1970.  "Leaching of
     Atrazine, Ametryne and Prometryne in the Soil."
     Journal of the Agricultural University of Puerto Rico
     54:5-18.

 62.  Scott, H. D. and R. E. Phillips. 1972. Diffusion of
     Selected Herbicides  in Soil."  Soil Science Society of
     America Proceedings  36:714-719.

 63.  U.S., Department of Agriculture,  Economic Research
     Service. 1983.    "Pesticides, Supply and Use." Inputs
     Outlook and Situation:   3 - 13.

 64.  Kerney, P. C.,  T. J. Sheets and J. W.  Smith.  1964.
     "Volatility of Seven S-Triazines. Weeds 12:83-86.

 65.  Pimentel, D. 1971. "Ecological Effects of Pesticides on
     Non-Target Species." Office of Science and Technology,
     U.S., Government Printing Office, Washington,  D.C.

66.  Gressel, J., Shimabukuro, R. H.  and M. E. Duysen. 1983.
     "N-Dealkylation of Atrazine and Simazine in Senecia
     vulgaris Biotypes: A Major Degradation Pathway."
     Pesticide Biochemistry and Physiology 19:361-370.
                          - 78 -

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67.  Jordan, L. S.f Farmer, W. J., Goodin, J. R. and B. E.
     Day.  1970.  "Nonbiological Detoxification of the S-
     Triazine Herbicides."  Residue Reviews 32:267-286.

68.  Khan, S. 1978. "Kinetics of Hydrolysis of Atrazine in
     Aqueous Fulvic Acid Solution." Pesticide Science 9:
     39-43.

69.  Hague, R., Kearney, P. C. and V. H. Freed. 1977.
     Dynamics of  Pesticides in Aquatic Environments."  In:
     Mohammed Khan ed.  Pesticides in Aquatic Environments.
     Plenum Press, New York, pp. 39-52.

70.  Smika, D. E. and E. D. Sharman. 1983. "Atrazine
     Carryover in Conservation Tillage Systems." Journal of
     Soil and Water Conservation 36(3): 239.

71.  Eichers, T. R. and W. S. Serletis. 1982. "Farm
     Pesticide Supply-Demand Trends, 1982."  .Economic
     Research Service, U.S. Dept. of Agriculture,
     Washington, D.C.

72.  Smith, C. N., Leonard, R. A., Langdale, G. W. and G.  W.
     Bailey.  1978.  "Transport of Agricultural Chemicals
     from Small Upland Piedmont Watersheds." Environmental
     Protection Agency. Athens, Georgia.

73.  Baker, J. L., Johnson, H. P., Borcherding, M. A. and W.
     R. Payne. 1977. "Nutrient and Pesticide Movement from
     Field to Stream: A Field Study." In:  R. C.  Loehr, D.
     A., D. A. Haith, M. F. Walter, and C. Martin, eds. Best
     Management Practices for Agriculture and Silviculture.
     Ann Arbor Science. Ann Arbor, MI.   pp. 213-246.

74.  Byass, J. B. and J. R. Lake. 1977. "Spray Drift from a
     Tractor-powered Field Sprayer." Pesticide Science
     8:117-126.

75.  Calderbank, A. and P. Slade. 1976. "Diquat and
     Paraquat."   In: P. C. Kearney and D.D. Kaufman, eds.
     Herbicides:  Chemistry Degradation, and Mode of Action.
     Volume 2.  Marcel Dekker, Inc. New York.  pp.  501-540.

76.  Riley, D.,  Wilkerson, W.  and B. V. Tucker. 1976.
     "Biological Unavailability of Bound Paraquat Residues
     in Soil."  In: Bound Conjugated Pesticide Residues.  D.
     Kaufaman, ed.  American Chemical Society. Washington,
     D.C. pp.  301-353.
                          - 79 -

-------
77.  Maas, R. P., Dressing, S. A., Kreglow, J. M., Koehler,
     F. A. and F. J. Humenik. 1982. "Best Management
     Practices for Agricultural Nonpoint Source Control:
     III." Sediment.  North Carolina Agricultural Extension
     Service, Biological and Agricultural Engineering Dept.
     N.C. State University Raleigh, N.C. 49 p.

78.  Hanthorn, M. and M. Duffy. 1983. "Corn and Soybean Pest
     Management Practices for Alternative Tillage Systems."
     Economics Research Service, U.S. Dept. of Agriculture.
     Inputs Outlook and Situation: 14 - 23.

79.  Johnson, G. S. and J. A. Moore. 1978. "The Effects of
     Conservation Practices on Nutrient Loss." Dept. of
     Agricultural Engineering, University of Minnesota.

80.  "Seasonal Runoff Losses of Nitrogen and Phosphorus from
     Missouri Valley Loess Watersheds."  Journal of
     Environmental. Quality 7(2): 203-207.

81.  Lake, J. and J. B. Morrison. 1977. "Environmental
     Impact of Land Use on Water Quality - Final Report on
     the Black Creek Project (Technical Report)." EPA
     905/9-77-007-B.  280 p.

82.  Kramer, "L. A. and R. E. Burwell. 1980. Land Use
     Treatment Effects on Claypan Soil Runoff and Erosion."
     ASAE Paper No. 80-2016. American Society of
     Agricultural Engineers.  St. Joseph, Mich.

83.  USDA - Soil Conservation Service. 1980. "Benefits/Costs
     of Soil and Water Conservation Practices for Erosion
     and Sediment Control."

84.  Burwell, R. E., Schuman, G. E., Piest, R. F. and R. G.
     Spomer. 1974. "Quality of Water Discharged from Two
     Agricultural-Watersheds in Southwestern Iowa."  Water
     Resources Research 10(2): 359-365.

85.  Dencly, F. E. 1974. "Sediment Trap Efficiency of Small
     Reservoirs." Transactions of the ASAE 17:898-908.

86.  Rausch, D. L. and J. D. Schreiber. 1981. "Sediment and
     Nutrient Trap Efficiency of Small Flood-Detention
     Reservoir." Journal of Environmental Quality
     10(3):288-293.

87.  Brown, M. J., Bondurant, J. A. and C. E. Brockway.
     1981.  "Ponding Surface Drainage Water for Sediment
     Phosphorus Removal." Transactions of the ASAE
     24(6):1478-1480.
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88.  Sweeten, J. M. and J. D. Price. 1974.  "Evaporation
     Ponds for Feedlot pesticide Reduction on the Texas High
     Plains Water Pollution." Texas Agricultural Experiment
     Station Publication No. 1126. lip.

89.  Bingham, S. W. 1973. "Improving Water Quality by
     Removal of Pesticide Pollutants with Aquatic Plants."
     Springfield, Va. 97 p.

90.  Valentine, J. P. and S. W. Bingham. 1974.  "Influence
     of Several Algae on 2-4-D Residues in Water."  Weed
     Science 22(4):358-363.

91.  Agrichemical Age. 1982. "California Applicators Fine-
     Tune Aircraft." Vol. 26(4):30-31.

92.  Agrichemical Age. 1983a. "ULV Technique has Multi-crop
     Future." Vol. 27(4):25.

93.  Hartley, G. S. and I. J. Graham-Bryce. 1980.  "Physical
     Principles of Pesticide Behavior, Vol. 2, Chapter 14:
     Application and Formulation." pp. 764-870.

94.  Yates, W. E. and N. B. Akesson. 1973. "Pesticide
     Formulations" W. van Valkenburg ed. Marcel Dekker, New
     York. p. 275.

95.  Ware, G. W., Apple, E. J., Cahill, W. P.  1982 Mist
     Blower vs Aerial Application of Sprays."   Journal of
     Economic Entomology 62(4):844-846.

96.  Boyd, J. D. 1979. "Better  Pests Control with Half the
     Chemical." Farm Journal 10:24.

97.  Wehtje,  G. R., Spalding, R. F., Orvin, C. B., Lowry, S.
     R.  and J. R. Leavitt. 1983.  Weed Science 31:610-618.

98.  U.S.  Environmental Protection Agency. 1980. "Research
     Summary, Integrated Pest Management." Washington D.C.
     EPA-600/81-80-044.  29 p.

99.  Council on Environmental Quality. 1980.  "Report to the
     President.  Progress Made  by Federal Agencies in the
     Advancement of Integrated  Pest Management prepared by
     the Interagency IPM Coordinating Committee."

100. Allen, G. E. and J. E. Bath.  1980. "The Conceptual and
     Institutional Aspects of Integrated Pest  Management."
     Bioscience 30(10):658-664.

101. Goldstein, J. and R. A. Goldstein. 1978.  "The Least is
     Best  Pesticide Strategy."  The J. G. Press,  Emmaus, PA.
     205 p.
                          - 81 -

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102. Huffaker, C. B. 1980. "New Technology of Pest Control."
     Wiley - Interscience. New York. 500 p.

103. Sill, W. H. Jr. 1982. "Plant Protection: An Integrated
     Approach." Iowa State University Press. 297 p.

104. Glass, E. H. 1975. "Integrated Pest Management:
     Rationale, Potential, Needs and Implementation."
     Entomological Society of America Special Publication
     75-2. 141 p.

105. Baldwin, F. L. and P. W. Santelmann. 1980. "Weed
     Science in Integrated Pest Management."  Bioscience
     30(10):675-678.

106. Agrichemical Age. 1983b. "Pick the Right Time to Spray
     Insects." Vol. 27(5):19E-20.

107. Day, B. E. 1-972. "Nonchemical Weed Control. In:  Pest
     Control Strategies for the Future."  Natural Academy of
     Science, Washington, D.C.  pp. 330-341.

108. Boutwell, J. L. and R. H. Smith. 1981. "A New Concept
     in Evaluating Integrated Pest Management Programs."

109. Apple, J. L. and R. F. Smith. 1976. "Integrated Pest
     Management." Plenum Press, New York. 200 p.

110. Hooper, N. K., Ames, B.  N., Saleh, N. M. and J. E.
     Casida.  1979. Science 205:591.

111. Matthews, G. A. 1979. "Pesticide Application Methods."
     Longman Inc. New York. 334p.

112. Smith, D. B., Goering, C. E., Leduc, S. K. and S. D.
     McQuigg. 1974.  ASAE Paper No. 74-1010. American
     Society of Agricultural Engineers. St. Joseph, Michigan
     49085.

113. Jolly, A. L. Jr. 1978. "Acute Toxicity of Permethrin to
     Several Aquatic Animals." Transactions of the American
     Fisheries Society 107(6):825-827.

114. National Science Foundation. 1975. "Integrated Pest
     Management:  the Principles, Strategies and Tactics of
     Pest Population Regulation and Control in Major Crop
     Ecosystems." Progress Report.  Volume 1.

115. Luckman, W. H. 1978. "Insect Control in Corn-Practices
     and Prospects."  In: Smith, E. H. and D. Pimentel. Eds.
     Pest Control Strategies,  pp. 137-155.
                          - 82 -

-------
116. Lewis, W. M. and A. D. Worsham. 1981. "Weed Management
     in No-Till."  In: No-till Crop Production Systems in
     North Carolina—Corn, Soybeans, Sorghum and Forage.
     N.C. Agricultural Extension Service.  Publication
     AG-273 p. 10.

117. Van Duyn, I. W. 1981. "Insect Problems in No-till
     Soybeans and Corn." N.C. Agricultural Extension
     Service. Publication AG-273 pp. 12-13.

118. Newsom, L. D. 1978. "Progress in Integrated Pest
     Management of Soybean Pests." In: Pest Control
     Strategies.  F. H. Smith and D. Pimentel, eds. Academic
     Press. N.Y.  pp. 157-180.

119. Slife, F. W. 1979. "Weed Control Systems in the Corn
     Belt States." In: Proceedings of the International
     Soybean Conference, pp. 393-398.

120. Bradley, I. R. and J. W. Van Duyn. 1979. "Insect Pest
     Management in North Carolina Soybeans." In: Proceedings
     of the International Soybean Conference, pp. 343-354.

121. Newsom, L. D., Kogan, M., Miner, F.D., Rabb, R. L.
     Turnipseed, S.G. and W. H. Whitcomb. 1980.  "General
     Accomplishments Toward Better Pest Control in Soybean."
     In: New Technology of Pest Control. C. B. Huffaker, ed.
     John Wiley and Sons. New York. pp. 51-98.

122. Frans, R. 1979. "Weed Control Systems in Southern U.S."
     In: Proceedings International Soybean Conference,  pp.
     399-407.

123. Rudd, W. G., Revsink, W. G., Newsom L. D., Herzog,
     D.C., Jensen, R. L. and N.F. Marsolan. 1980. "The
     Systems Approach to Research and Decision Making for
     Soybean Pest Control."  In: New Technology of Pest
     Control, C. B. Huffaker, ed.  John Wiley and Sons. New
     York. pp. 99-122.

124. Wilkerson, G. G., Mishoe, J. W., Jones, J. W., Boggess,
     W. G. and D. P. Swaney. 1983.  "Within-Season Decision
     Making for Pest Control in Soybeans.  ASAE Paper No.
     83-4044.  American Society of Agricultural Engineers.
     St. Joseph, Michigan. 18p.

125. Vinten, A. J., Yaron, B. and P. H. Nye. 1983. "Vertical
     Transport of Pesticide into Soil when Adsorbed on
     Suspended Pesticides." Journal of Agricultural and Food
     Chemistry 31:662-664.
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126. Baker, J. L., Laflen, J. M. and R. O. Hartwig. 1982.
     "Effects of Corn Residue and Herbicide Placement on
     Herbicide Runoff Losses." Transactions of the ASAE
     25(2):340-343.

127. Casey, J. E.f Lacewell, R. D. and W. Sterling. 1975.
     "An Example of Economically Feasible Opportunities for
     Reducing Pesticide Use in Commercial Agriculture."
     Journal of Environmental Quality 4(l):60-64.

128. Phillips, J. R., Gutierrez, A. P. and P. L. Adkisson.
     1980. "General Accomplishments towards Better Insect
     Control in Cotton." In: New Technology of Pest Control.
     C. B. Huffaker, ed. John Wiley and Sons. New York.
     Chapter 5. 123-153.

129. Gutierrez, A. P., De Michele, D. W., Wang, Y., Curry,
     G. L., Skeith, R. and L. G. Brown. 1980. "The Systems
     Approach 'to Research"and Decision Making for Cotton
     Pest Control."  In: New Technology of Pest Control. C.
     B. Huffaker, ed. John Wiley and Sons. New York. Chapter
     6. 155-186.

130. Hall, D. C. 1977. "The Profitability of Integrated Pest
     Management:  Case Studies for Cotton and Citrus in the
     San Joaquin Valley."  Entomological Society of America
     Bulletin 23(4):267-274,

131. Lacewell, R. D., Spratt, J. M., Niles, G. A., Walke, J.
     K.  and J. R. Gannaway. 1976. "Cotton Grown with an
     Integrated Production System." Transactions of the ASAE
     19(5):815-818.

132. Rabb, R. L., Todd, F. A. and H. C. Ellis. 1976.
     "Tobacco Pest Management." In: Integrated Pest
     Management. Apple, J. L.  and R. F. Smith, eds. Plenum
     Press, N.Y. pp. 71-102.

133. Croft, B. A. 1978. "Potentials for Research and
     Implementation of Integrated Pest Management on
     Deciduous Tree-Fruits."  In: Pest Control Strategies.
     E. H. Smith and D. Pimentel. eds.  Academic Press, New
     York. pp. 101-116.

134. Eisher, G. C. and R. Weinzierl. 1981. "Integrated Pest
     Management and Its Potential Application in Small
     Fruits Production." Annual Report-Oregon Horticultural
     Society 72:95-99.

135. Hoyt, S. C. and J. D. Gilpatrick. 1976. "Pest
     Management on Deciduous Fruits: Multidisciplinary
     Aspects." In: Integrated Pest Management. J. L. Apple
     and R. F. Smith Eds. Plenum Press, New York. pp.
     133-147.

                          - 84 -

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 136.  Brunner,  J.  1981 "New Tactics for Apple IPM."
      Washington State Horticultural Association Proceedings
      of Seventy-Seventh Annual Meeting:  145-150.

 137.  Willey, W. R.  1978.  "Barriers to the Diffusion of IPM
      Programs  in  Commercial Agriculture." In:  Pest Control
      Strategies.  E.  H.   Smith and D.  Pimentel,  eds.  Academic
      Press, New York.  pp.  285-308.

 138.  Murdock,  C.  W.,  Leach, S.  S.  and L.  J.  Potaro.  1982.
      "Integrated  Pest  Management-Biological  Control  of
      Potato Pathogens." Maine Agricultural Extension
      Service,   pp.  98-100.

 139.  Thurston,  D. H.  1978.  "Potentialities for  Pest
      Management in  in  Potatoes."  In:  Pest Control
      Strategies." E. H. Smith and  D.  Pimentel,  eds.  Academic
      Press, New York.  pp.  117-135.

 140.  U.S. Dept. of Agriculture, Agricultural Research
      Service.   1983. "Better  Biocontrol,  Less Insecticide."
      Agricultural Research  31(10):15.

 141.  Tew, B. V., Wetzstein, M.  E.,  Epperson, J. E.,  and J.
      D.  Robertson. 1982.  "Economics  of Selected Integrated
      Pest Management Production Systems in Georgia."
      University of Georgia."  Experiment Station. Research
      Report 395. 12p.

 142.  Aly, O. M. and M. A. El-Dib 1971. "Hydrolysis of  Sevin,
      Baygon, Pyrolan and Pimetilan  in Waters." Water
      Research 5(2):1191-1205.

 143.  Beyerlein, D. C. and A.  S. Donigian  Jr. 1979. "Effects
      of Soil and Water Conservation Practices on Runoff and
      Pollutant  Loss from Small Agricultural Watersheds: A
      Simulation- Approach."  In:. Effectiveness of Soil and
     Water Conservation Practices for Pollution Control. EPA
      600/3-79-106. pp. 385-473.

 144. Johnson,  D. D., Kreglow, J. M., Dressing, S. A., Maas,
     R. P.,  Koehler, F. A. and F.  J. Humenik. 1981.
      "Annotated Bibliography of Source Documents."
     Biological and Agricultural Engineering Department.
     North Carolina State University, Raleigh, NC.

145. Wu, T.  L., Correll, D. L. and H. E.  Remenapp.  1983.
      "Herbicide Runoff from Experimental Watersheds."
     Journal of Environmental Quality 12:330-336.

146. Leonard,  R. A., Langdale, G.  W. and W. G. Fleming.
     1979.   "Herbicide Runoff from Upland Piedmont
     Watersheds-Data and Implications for Modeling Pesticide
     Transport." Journal of Environmental Quality 8:223-229.

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147. Baker, J. L. and J. M. Laflen.  1983 "Water Quality
     Consequences of Conservation Tillage." Journal of Soil
     and Water Conservation 38(3):186-193.

148. Martin, C. D., Baker, J. L., Erbach,  D. C. and H. P.
     Johnson.  1978. "Washoff of Herbicides Applied to Corn
     Residue." Transactions of the ASAE 21:164-168.

149. Hall, J. K., Hartwig, N. L. and L. D.  Hoffman.  1984.
     "Cyanazine Losses in Runoff from No-Tillage Corn in
     'Living'and Dead Mulches vs. Unmulched, Conventional
     Tillage." Journal of Environmental Quality 13:105-110.

150. Jones, T. W. and L. Winchell.  1984. "Uptake and
     Photosynthetic Inhibition by Atrazine and its
     Degradation Products on Four Species of Submerged
     Vascular Plants." Journal of Environmental Quality
     13(2): 243-247.

151. Willis, G. H., McDowell, L. L., Murphree, C. E.,
     Southwick, L. M. and S. Smith Jr. 1983. "Pesticide
     Concentrations and Yields in Runoff from Silty Soils  in
     the- Lower Mississippi Valley." Journal of Agricultural
     Food Chemistry 31: 1171-1177.

152. Harper, L. A., McDowell, L. L., Willis, G. H., Smith,
     S.  and L. M. Southwick. 1983. "Microclimate Effects on
     Toxaphene and DDT Volatilization from Cotton Plants."
     Agronomy Journal 75: 295-302.

153. Hansen, D. J., Goodman, L. R., Moore, J. C. and P. K.
     Higdon. 1983. "Effects of the Synthetic Pyrethroids AC
     222, 705, Permethrin and Fenvalerate on Sheepshead
     Minnows in Early Life Stage Toxicity Tests."
     Environmental Toxicology and Chemistry 2: 251-258.

154. Lazarus, W. F. and E. R. Swanson, 1983. "Insecticide
     Use and Crop Rotation Under Risk: Rootworm Control in
     Corn." American Journal of Agricultural Economics 65:
     783-747.

155. Food and Drug Administration. 1984. "Surveillance Index
     for Pesticides Update." NTIS - PB84 -  913200,
     Washington, DC

156. Rao, P. S., Berkheiser, V. E. and L. T. Ou. 1984.
     "Estimation of Parameters  for Modeling the Behavior of
     Selected Pesticides and Orthophosphate."  EPA  -
     600/3-84-019. 181p.

157. Baker,  D. B.  1983.  "Herbicide Contamination, in
     Municipal Water Supplies of Northwestern  Ohio."   Final
     Report  to EPA Heidelburg College, Tiffin, Ohio.  33p.
                           -  86  -

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158. Gebhardt, M.R., Bouse, L. F.  and  C.  L.  Webber.  1984.
     "Herbicide Application With  the Controlled Droplet
     Applicator When Using Soybean Oil."  ASAE Paper  No
     83-1509.  ASAE, St. Joseph,  Michigan,  lip.

159. Maas, R. P., M. D. Smolen, S.  A.  Dressing 1984.
     Selection of Critical Areas  for Control of Nonpoint
     Source Pollution.  Journal of Soil  and Water
     Conservation - (In Review).

160. Kosinski, R..J. and M. G. Merkle  1984.   The Effect of
     Four Terrestial Herbicides on the Productivity  of
     Artifical Stream Algal Communities.   Journal of Quality
     13(1): 75-82.

161. Heimlich, R.E. and N. L. Bills. 1984.   An Improved Soil
     Erosion Classification for Conservation Policy.
     Journal of Soil and Water Conservation.  39(4):
     261-267.
                           - 87 -
                                             *U.S. Government Printing Office: 1992—648-003/40764

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