Wildlife and Pesticides: A practical guide to reducing the risk
WL-1017
Terry Messmer, Wildlife Specialist
Greg Dahl, Pesticide Program Specialist
Pesticides are widely used in agriculture today. Producers use
pesticides because they are effective and generally reasonably priced. The benefits
include reduced yield losses and time savings to the producer, and lower food and fiber
costs for consumer.
There are some downside risks to pesticide use. Pesticide poisonings of people,
livestock, and wildlife have occurred when proper care was not exercised. Pesticide
applicators must be very careful to avoid these risks.
Pesticides, when used with good judgement and care in accordance with label
instructions, benefit both agriculture and the environment. Proper use ensures that food
and wildlife production objectives can both be realized.
Every pesticide applicator must accept responsibility to prevent or minimize the
effects of pesticide applications on nontarget organisms. There are several things you as
an applicator can do to reduce the risk of pesticide exposure to nontarget plants, animals
and habitats.
Potential Hazards to Wildlife
In order to better protect wildlife from the risks of pesticide exposure it is
necessary to understand what effects pesticides may have on wildlife.
Several hundred different pesticides are used in agriculture today. Each one of these
products has different characteristics that can affect the risk posed to different types
of wildlife. While a particular pesticide may pose no harm to mammals, it may cause severe
harm to aquatic or bird life. Knowing these differences will greatly assist you in making
the proper pesticide use decision.
There is much documentation showing that wildlife can be harmed by particular
pesticides. The documentation includes laboratory toxicity studies on various types of
wildlife, field trials that must be performed in order to register the pesticide, and
reports of incidents of wildlife poisoning.
In Oregon in the 1970s, aldrin and mercury treated seed grain killed thousands of wild
geese and other wildlife. Thirty-six Canada geese were killed in 1988 as a result of an
application of carbofuran (Furadan) and disulfoton (Di-Syston) in Idaho. Phorate (Thimet)
was involved in the deaths of hundreds of waterfowl and several bald and golden eagles in
South Dakota in 1989.
Many of the incidents involving wildlife kills result from misuse or illegal
applications. One such incident occurred in 1990 when an applicator in North Dakota
illegally applied carbofuran (Furadan) to carcasses for predator control. He was found
guilty of killing several forms of wildlife, possibly including a bald eagle.
Effects of Pesticides on Wildlife
Pesticides' effects on wildlife may be lethal, sublethal, acute, chronic, habitat
related, or there may be no effect. In general the risk a pesticide poses to wildlife is
related to the pesticide type, its toxicity, the proximity of the application to wildlife
habitat, the dose, application rate, number of applications, the persistence of the
pesticide in the environment, and its ability to concentrate in the wildlife food chain.
These factors interact with food habits and behavior of individual wildlife species to
produce a response.
Pesticide Type
In general, insecticides are more toxic to fish and wildlife than herbicides or
fungicides. Some herbicides may harm wildlife by damaging the wildlife habitat.
Many of the insecticides currently used are either the organophosphate or carbamate
type. These insecticides work by interfering with the central nervous system of insects.
The central nervous system of fish or wildlife may be affected the same way. The toxicity
of the various organophosphate and carbamate insecticides ranges from slightly toxic
products to products that are highly toxic. The more toxic products are generally restricted
use pesticides which require applicators to be certified by their state regulatory
agency to purchase and apply products.
Synthetic pyrethroid insecticide use has been increasing. These synthesized
insecticides are based on naturally occurring pesticides, but have been modified to
improve performance and persistence. Synthetic pyrethroids also work by interfering with
the central nervous system. Synthetic pyrethroids are low to medium in toxicity to mammals
and birds because they can quickly detoxify and excrete them. However, fish and aquatic
invertebrates can not quickly detoxify or excrete synthetic pyrethroids, so they are
highly susceptible to poisoning by these products.
Herbicides and fungicides are generally low to moderately toxic to wildlife. Particular
herbicides can have a large impact on the plant life making up the wildlife habitat.
Wildlife can be exposed to pesticides directly by eating contaminated food or water,
breathing pesticides, or by skin absorption.
The type and magnitude of the effect depends on two factors, the pesticide toxicity and
pesticide quantity (dose). If exposure causes the animal's death, it is referred to as a
lethal effect.
Young birds that eat or are fed pesticide treated insects are at great risk of
suffering lethal pesticide exposure effects. Sublethal insecticide effects occur when
damage to the central nervous system causes an animal to behave in a unusual manner. This
behavior may affect the animal's ability to survive or reproduce. Some typical sublethal
responses in birds exposed to pesticides include the inability to sing properly, establish
a breeding territory, or attract a mate. Adults may be unable to care for themselves or
their young properly, resulting in death to the nestlings or increased chance of
predation.
The lethal and sublethal effects of pesticides on wildlife and fish may occur from one
exposure over a short time period (acute) or they may result from exposures to small
amounts over a longer time period (chronic). Pesticides commonly used today do not persist
as long in the environment as pesticides used years ago. The tradeoff is that the acute
toxicity of some of these modern pesticides is higher than the older, more persistent
chemicals.
Wildlife in general, and birds in particular, may also experience lethal or sublethal
effects without being directly exposed to a pesticide. This typically occurs when a
pesticide application destroys or disrupts food sources such as insects. Insects supply
the protein necessary for growing birds. Studies indicate that the growth of young birds
can be stunted in areas where insecticides have been used heavily, resulting in insect
populations too low to meet young bird protein growth demands. Fish that feed on aquatic
insects and animals may also show stunted growth in areas of heavy insecticide use because
their primary food sources are killed. Inadequate diets also can affect fish reproduction
and survival. Herbicides can reduce the amount of cover and make the habitat less suitable
for nesting.
Assessing Pesticide Risk to Wildlife
To properly assess the need for pesticides and the risk to wildlife, information must
be gathered on the condition of the crop, the pest situation, characteristics of candidate
pesticides, present and expected weather, and some knowledge about the kinds and behavior
of wildlife living in the area. The importance of good judgement, practical experience and
common sense cannot be overemphasized. Prior to each and every pesticide application, the
overall situation should be evaluated so that the expected benefits of a pesticide
application are realized and potential hazards are minimized. Good information is
necessary to make good judgements.
Monitor Fields Regularly
Field scouting must be done. It is important to be aware of the status of
the field, the crop stage, general health, and yield potential of the crop, as well as the
number and growth stage of the various pests that are present. Careful scouting will
reveal any wildlife that may also be present. Most pests and most wildlife do not occur
uniformly throughout a field. Drawing a map of the field showing the locations of pest
populations and wildlife along with recognizable landmarks can aid you in developing a
pest control plan that avoids possible effects on wildlife.
Identify Wildlife Signs, Seasons, and Habitats
One way to ensure that wildlife will not be impacted by a pesticide is to make the
application when wildlife are not present. Most wildlife signs can be easily determined
while scouting the field. Virtually all agricultural crops will support some type of
wildlife. A wide assortment of wildlife will likely be visible during most scouting trips.
Areas where wildlife are most likely to be located are field perimeters and other areas
where fields may come into contact with windbreaks, wetlands, livestock watering ponds,
fencerows, abandoned farmsteads, grasslands or odd areas.
Take note of areas where you actually see animals. Other evidence that wildlife are
present and using the area includes signs such as tracks, droppings, or foraging evidence.
If numerous wildlife signs are present, pesticide applicators can reduce potential
impacts to wildlife by marking such areas on a field map or leaving a flag in that area of
a field. When spraying around sensitive areas, leave a buffer zone of at least one-half
the width of a sprayer boom. Another way to minimize potential impacts to wildlife is to
restrict spraying activities in these fields between the hours of 10 a.m. and 4 p.m.
During this period, many wildlife will seek the protective cover of cropland, particularly
taller row crops, as they wait out the day prior to beginning evening and early morning
foraging activities.
Critical Reproductive Periods and Habitats
Most wildlife reproduction occurs from May 1 to late June and early July. This is
perhaps the most critical for many of our resident and migratory wildlife and fish. To
complete this reproduction, animals seek out suitable habitats.
These habitats can include wetlands, windbreaks and shelterbelts, fencerows,
rangelands, and croplands. Wildlife typically nest, birth, feed, and rear their young in
areas that provide not only some type of protective cover from the elements and potential
predators, but also sources of food.
The transition zones between habitat types, where one plant community changes to
another, are preferred. These edges usually produce the greatest variety of food plants,
insects and seeds. This allows wildlife such as grouse, pheasants, and deer to feed
without venturing too far from protective cover. For this reason, most upland gamebird
nests can be found in or near such edges.
Wetlands are important feeding and brood rearing habitats for waterfowl. Insecticides
applied near wetlands by ground sprayers or aircraft can enter the habitat through drift
or runoff and contaminate these areas. Depending on the insecticide type, food sources may
be destroyed, causing sublethal effects or a direct loss of young wildlife.
Similarly, shelterbelts and windbreaks are important habitats for many songbirds.
Herbicide drift that results in injury to trees and other vegetation can impair the
ability of such habitats to provide safe, secure nesting sites. Insecticide drift can kill
nestlings and adult birds, as well as contaminate important insect food sources.
Reducing Pesticide Exposure Risk
Regular field scouting and a pest control plan should be a part of every producer's
operation. Pests are best controlled by manipulating cropping conditions to put pests at a
disadvantage to the crop or beneficial organisms. Man and his crops are in competition
with pests, and ALL available methods for controlling pests should be considered, not just
pesticides.
Eliminate Unnecessary Pesticide Applications Through IPM
Few applicators knowingly apply unnecessary pesticides because pesticides cost money.
Every applicator should ask, will this application pay for itself? Growers should not
substitute pesticides for good management. Pesticides are necessary but should only be
part of a total pest control program, not the entire program.
The best method of reducing risks to wildlife is to use integrated pest management
(IPM) practices. IPM incorporates cultural methods such as crop rotation, date of
planting, variety choices, and seeding rates with other methods of pest control to
maintain pest populations at tolerable levels. Under IPM, pesticides are used only when
other methods are not successful and pest damage to crops might otherwise exceed the cost
of control.
Many pest management practices can help reduce the need for pesticides. Some additional
control methods include crop competition, crop rotation, tillage and cultivation,
sanitation, planting resistant varieties, planting weed and disease free seed, and using
the natural controls present when possible.
A good example of non-pesticide control is a competitive crop. An early established,
well developed crop can do much to help control weeds. Plants emerging first have a
competitive advantage over later emerging plants. Anything done to get quick crop
emergence that evenly covers the ground early will have a big impact on weeds. Later
emerging weeds are at a tremendous disadvantage and may not cause yield and quality
losses. The competitiveness of weeds and crops differs between species. Weeds such as wild
oats, wild mustard, and kochia are very competitive, while others, such as redroot pigweed
and foxtails are generally less competitive. Some crops ranked in order of decreasing
competitiveness are rye, barley, conventional height wheat, semidwarf wheat, and flax.
Choose the Pesticide Least Toxic to Non-target Organisms
Choose the least toxic pesticide that will control the pest. Often more than one
pesticide is registered for control of a particular pest in a particular crop. Take time
to compare pesticides and make sure you choose the one BEST suited for the job. Many times
the best choice will be the least expensive treatment, but that is not always the case.
Sometimes the best choice would be a higher priced pesticide with fewer risks for
nontarget plants and animals.
Pesticide Toxicity to Wildlife
Pesticide applicators can plan a pesticide application that is less toxic to wildlife
by examining pesticide toxicity and potential for environmental injury to wildlife and
wildlife habitats. This information can be found in tables presented in the back of this
publication.
When an applicator has identified the specific crop pest situation and checked local
crop production guides, a pesticide can be selected that minimizes risk to nontarget
plants and animals and still achieves the desired level of control.
If the selected pesticide still poses a high threat to wildlife, the applicator would
at least be aware of the risk and can take the steps to minimize any potential threats by
following recommendations in this publication.
Read the Pesticide Label
Certain pesticides pose a risk to wildlife or the environment. Some products are
classified as RESTRICTED USE PESTICIDES because of environmental hazards. Restricted use
pesticides should only be applied by a certified applicator who has been properly trained.
Pesticides that pose environmental risks are labeled to warn the applicator what the
risks could be and what steps should be taken to protect people, animals and the
environment. These warnings can be found in the "Precautionary Statements"
section of the label. The precautionary section is divided into subsections dealing with "Hazards
to Humans or Domestic Animals," Environmental Hazard" and "Physical
or Chemical Hazard." The risks to wildlife and the environment may be found in
the "Environmental Hazard" section. It is a violation of federal law to apply
pesticides in any way that is not consistent with label instructions.
If a particular pesticide is especially hazardous to wildlife, it will be stated on the
label. For example:
- This product is highly toxic to bees.
- This product is toxic to fish.
- This product is toxic to birds and other wildlife.
The label may indicate that the product causes undesirable effects in the environment.
In this case, the precautionary statement may tell what to avoid doing. Labeling may
indicate limitations imposed to protect wildlife, including endangered species. These
limitations may include reduced rates, restrictions on types of application, or a ban on
the pesticide's use within the species range. The label also may indicate additional
sources of information on proper application methods to reduce hazards.
These statements explain special hazards that the pesticides may pose. They should help
when choosing the safest product for a particular job and serve as a reminder to take
extra precautions.
General Environmental Statements
General environmental statements appear on nearly every pesticide label as reminders of
common sense actions needed to avoid contaminating the environment. The absence of any or
all of these statements DOES NOT change the requirement to take adequate precautions.
Sometimes the statements will follow a "specific toxicity statement" and
provide practical steps to avoid harm to wildlife.
Examples of general environmental statements include:
- Do not apply when runoff is likely to occur.
- Do not apply when weather conditions favor drift from treated areas.
- Do not contaminate water when cleaning equipment or disposing of wastes.
- Keep out of any body of water.
- Do not allow drift on desirable plants or trees.
- Do not apply when bees are likely to be in the area.
- Do not apply where the water table is close to the surface.
Note: It is the responsibility of every pesticide applicator to read and follow the
label directions.
Use the Lowest Effective Rate
Many times the label will allow a range of rates to control a particular pest.
Differences in pest size or stage, pest populations and environmental conditions can
affect the amount of pesticide needed. Often pesticide rates at the lower end of the rate
range can be used when pests are in sensitive growth stages, at lower populations and the
weather and growing conditions are favorable.
An area between the area sprayed and a sensitive area is called a buffer zone. This
area can be a grass strip or may even be part of the crop that is not treated. This buffer
area will help trap pesticides and prevent them from entering sensitive areas by spray
drift or by runoff.
Spot Spraying
Many times a pest is located only in a portion of the field. Spraying only the area
where the pest is found, leaving the rest of the field untreated, reduces potential risks
and saves time and money.
Begin Spraying In the Middle of the Field
Most wildlife will be present near the edges of a field. Spraying the field by starting
in the middle of the field will allow wildlife time to escape or move out of the field
area.
Some farmers are experimenting with the use of trap areas. Farmers will seed these
areas with an early maturing crop variety ahead of normal planting dates. These areas may
attract pests and if pest populations develop in the trap area, a pesticide application
can be made. Controlling pests in this manner can reduce chances that pesticides will be
required on the rest of the field.
Check Weather Conditions
A good applicator always checks the weather conditions before spraying. Weather
conditions can greatly affect the pesticide exposure through spray drift or runoff. Don't
apply pesticides just before rains because pesticides could run off the treated field with
excess rainwater and potentially contaminate sensitive areas. Avoid spraying when weather
conditions could cause spray drift into sensitive areas.
Avoid Spray Drift
Spray drift can cause damage to wildlife or wildlife habitat. The following measures
are available to greatly reduce drift.
Avoid spraying on windy days
Check the wind speed and direction. If conditions could cause spray drift into
sensitive areas, don't spray. If an application must be made you must take every
precaution you can to prevent drift from entering sensitive areas.
Another weather condition to avoid is a temperature inversion. Temperature inversions
occur when cooler air is near the ground and is beneath warmer air. Very small spray
droplets will remain suspended in the air and can move some distance.
Use a nonvolatile formulation
Some pesticides are volatile and can form vapors, usually on warmer
(greater than 70 F) days, which can drift into susceptible areas. If there is an
alternative pesticide or formulation that is not volatile and will control the pest, it
should be used instead.
Increase Droplet Size
Spray nozzles produce spray droplets of many different sizes. Larger
droplets are heavier and drift less. Practices that increase droplet size will reduce
drift, such as increasing nozzle size or water volume, reducing spray pressure or using a
drift retardant.
Use Larger Nozzle
Larger nozzles allow you to apply the same volume of spray with less spray
pressure. Spray droplets will be larger than those produced by a smaller nozzle with
higher pressure.
Increase Water Volume
Increasing the water volume will decrease drift because water droplets
will be larger and will tend to drift less.
Use the Lowest Practical Pressure
Lower spray pressure will result in larger spray droplets that drift less
than smaller droplets. If spray pressure is reduced too much the spray pattern that
results will not be uniform. Newer nozzles such as the "LP" or "XR"
type are designed to produce uniform spray patterns with pressures of 15 to 20 pounds per
square inch.
Use a Drift Retardant
A drift retardant will help reduce spray drift by increasing the size of
spray droplets. Larger droplets tend to drift less than small droplets.
Reduce Spray Boom Height
Set spray booms at the lowest height that will give uniform coverage. The
closer the boom is to the spray target the less chance there is for drift.
Use a Shielded Sprayer
Using a shielded sprayer will help reduce spray drift by protecting the spray from wind.
Shielded sprayers allow a wider selection of spraying times during the day and more total
spraying time per day. These time savers can be used to more precisely target crop areas
and avoid sensitive areas. More information on spray drift can be found at your state's
Cooperative Extension Service county office.
The responsibility to prevent or minimize the effects of pesticide applications on
nontarget organisms rests with every pesticide applicator. Information concerning the
proper use and application of a pesticide can be found on the product label.
Reducing the risk of pesticide exposure to nontarget organisms requires applicators to
incorporate crop scouting and IPM techniques with a knowledge of wildlife life cycles and
habitats in developing a farm pesticide application plan. Development of such a plan will
insure not only the most cost effective means for controlling crop pest situations, but
also result in the greatest reduction of risk of pesticide exposure to wildlife.
Resource Material
Apply Pesticides Correctly: A Guide for Commercial Applicators, U.S. Department
of Agriculture and U.S. Environmental Protection Agency.
Commercial and Private Applicator Core Manual: Initial Certification, September
1989, Cooperative Extension Service, Michigan State University.
Dexter, A. Herbicide Spray Drift. 1986. NDSU Extension Service. A-657 revised.
Extoxnet Cooperative Extension Offices, Cornell, U of Calif., Michigan State, Oregon
State Univ.
Facemire, F. Charles, 1991. Impact of agricultural chemicals on wetland habitats and
associated biota with special reference to migratory birds. B 780, SDSU, Brookings,
SD. 65 pp.
Herbicide Handbook of the Weed Science Society of America. Sixth Ed., 1989, Weed
Science Society of America, Champagne, Illinois, 61820.
McBride, D.K., D.E. Peterson, H.A. Lamey, 1988, Persistence and Mobility of
Pesticides in Soil and Water, NDSU Extension Service. E-49, NDSU Fargo, ND 58105
Pesticide Applicator Training Manual: Core Manual, 2nd Ed., Chemicals-Pesticides
Program, Cornell University, 1990. D. Rutz, Director, R. Gardner, W. Smith.
Pesticide Education Manual: A Guide to Safe Use and Handling, College of
Agriculture, Pennsylvania State University.
Smith, G.J., 1987. Pesticide use and toxicology in relation to wildlife: Organ
phosphorus and carbamate compounds. Res. Publ. 170, U.S. Fish and Wildlife Service,
Washington D.C. 171 pp.
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WL-1017
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