B-5094

Most cotton farmers appreciate wildlife. They enjoy seeing wildlife on their farms and some benefit economically by leasing hunting and fishing rights to sportsmen. Cotton fields provide food and cover for several species of wildlife. Quail and other birds, for example, nest along fencerows or in rangeland surrounding cotton fields and enter cotton fields to feed or pick up grit. Pesticides applied to these fields can potentially harm wildlife.

In recent years the public has become more concerned about pesticides and their effects on the environment. From 1987 to 1989, Texas farmers and ranchers treated an average of 15 million acres with insecticides and 20 - million acres with herbicides. As stewards of the land and natural resources, farmers and ranchers should strive to use pesticides properly in order to minimize environmental risks.

The proper use of pesticides helps ensure that Americans have a safe, abundant and inexpensive supply of food and fiber. Pesticides improve crop yields and quality, and help to make farming practices profitable. Sometimes, however, pesticides can threaten wildlife and wildlife habitat.

How Wildlife Are at Risk

Wildlife are directly exposed to pesticides when they eat plants or seeds with chemical residues or when they swallow the pesticide granules themselves. They are exposed indirectly when they eat insects or other animals killed by chemicals. Wildlife that are in fields when pesticides are applied, or that enter fields shortly B afterward, may inhale vapors or get pesticides on their skin or in their eyes. Pesticides on an animal's skin or feathers may be swallowed when the animal grooms or preens itself. Pesticides washed by heavy rains into streams, ponds or other wetlands can harm aquatic animals.

The hazard of a particular pesticide to any species of wildlife is a product of two factors-the chemical's toxicity and an animal's degree of exposure to the chemical. The toxicity of a pesticide is commonly expressed as either its LD₅₀ (lethal dose) or LC₅₀ (lethal concentration). The LD₅₀ of a particular chemical is the dose that kills 50 percent of the animals exposed to it. The LC₅₀ is the concentration of the chemical in the diet, air or water required to kill 50 percent of the animals exposed. LD₅₀s and LC₅₀s vary among different animal species and are determined by laboratory research. However, for any species, the lower the LD₅₀ or LC₅₀, the more toxic the chemical.

Exposure to a highly toxic pesticide can cause sickness and death. Sublethal doses (doses not large enough to kill an animal) may make an animal sick and alter its behavior. The sickened animal may not return to normal health for several weeks following exposure. Animals made sick by a pesticide are more likely to die if they are exposed again. Repeated exposure to some pesticides such as diazinon has reduced egg production in birds and decreased body weight in birds and mammals. Small, repeated doses of parathion can reduce the ability of bobwhites to survive very cold temperatures. Sublethal doses also may make animals more vulnerable to predators.

Besides its toxicity, a pesticide's hazard to wildlife is also based on the way it is used and othercharacteristics, such as its persistence in the environment. For example, methomyl (Lannate®) is highly toxic to birds and mammals. However, because methomyl does not persist in the field, careful use of this chemical presents only a moderate hazard to wildlife. In Tables 1 and 2, pesticides with ratings of "High" may cause wildlife to die or become sick; a "Moderate" rating means a pesticide may cause sickness, but deaths are unlikely; a "Low" rating means the chemical is unlikely to harm terrestrial wildlife when used according to label directions. Hazards may increase for fish or other aquatic organisms.

Using Herbicides Safely

About 70 percent of the pesticides used in the U.S. are herbicides. Most herbicides used on cotton in Texas are only slightly toxic to birds and mammals (Table 1). One exception is paraquat (Gramoxone Extra®, Cyclone®), which is toxic to birds and bird embryos. Some herbicides are highly toxic to fish. These include fluazifop (Fusilade 2000®), fluometuron (Cotoran®), pendimethalin (Prowl®) and trifluralin (Treflan®).

Table 1. Toxicity of Herbicides Used in Cotton.

The greatest risk to wildlife from herbicides is the affect they may have on habitat. Many birds and mammals nest or feed in or near cotton fields, especially when fields border rangeland. Wildlife rely on the trees, brush or grass near fields for food and cover. Fencerows, turnrows, borrow ditches, field borders and shelterbelts are important habitats for gamebirds such as quail, pheasants and mourning doves, as well as many species of songbirds and small mammals. Many "weeds" to the farmer (pigweed, sunflower), are important food sources for birds.

Farmers can provide wildlife habitat near crop areas by planting filter strips. These are strips of land planted to permanent grasses that separate croplands from streams or other wetlands. Filter strips also help to protect water quality by keeping rainfall from washing pesticides and soil into streams. Filter strips should Q be at least 30 feet wide, and preferably up to 100 feet, to make them useful to g wildlife. Cost-sharing programs may be available for developing filter strips. Contact E your local Soil Conservation Service office for details.

Using Insecticides Safely

Insecticides are typically much more toxic to wildlife than herbicides. Insecticides commonly used in cotton are classified into five main groups:

• organochlorines

• organophosphates;

• carbamates;

• synthetic pyrethroids; and

• microbials.
  

One way to reduce the effects of insecticides on wildlife is to use the least toxic product possible. The toxicities of some common cotton insecticides to wildlife are listed in Table 2. Organochlorines, the family of insecticides that contained DDT, dieldrin and aldrin, are rarely used today. Most were banned because of their persistence in the environment and their tendency to biomagnify, or increase in concentration in animals at each higher level of the food chain. Some of the less persistent organochlorine insecticides are still used in cotton production in the U.S.

Table 2. Toxicity of Common Insecticides and Nematicides Used on Cotton to Birds, Mammals amd Fish.

They include lindane used as a seed treatment, endosulfan (Thiodan® or Phaser®), dicofol (Kelthane®) and propargite (Comite®) used as foliar sprays.

Organophosphate and carbamate insecticides are commonly used on cotton. These are much less persistent in the environment than organochlorines. However, they are more acutely toxic and even small doses of some may cause immediate and severe poisoning.

There is a wide range in the toxicity of organophosphates ranging from less toxic products such as malathion (Cythion®) to much more toxic products such as disulfoton (Di-Syston®) or methyl parathion. Carbamates also range from less toxic products such as carbaryl (Sevin®) to highly toxic products such as oxamyl (Vydate®) and aldicarb (Temik®).

Synthetic pyrethroids are the newest class of insecticides commonly used in cotton. Examples include cyfluthrin (Baythroid®), cyhalothrin (Karate®), esfenvalerate (Asana XL®) and cypermethrin (Ammo®). They are generally less hazardous to wildlife than organophosphates or carbamates. However, synthetic pyrethroids are extremely toxic to fish and aquatic invertebrates.

Microbial insecticides are another relatively new group of insecticides. The only one currently in use is Bacillus thuringiensis (Bt), a bacterium that kills certain insects but does not harm other animals or plants. Other microbial insecticides containing bacteria, fungi or viruses are expected to be labelled in the near future. In addition, genetically engineered cotton plants containing Bt genes should be registered for use by the mid-1990s. Substituting microbial insecticides for chemical insecticides, where practical, will reduce hazards to wildlife. One way to reduce the effects of insecticides on wildlife is to use the least toxic product possible.

Insecticides can be applied as sprays, granules, dusts or baits. Spray and granular formulations are most common in cotton production. Sprays are usually applied to growing plants, while granules are generally applied at planting time.

Granular Insecticides

Granular insecticides are often applied as cotton is planted to protect the crop from thrips, aphids and other pests. The granules are dropped into the seed furrow and covered with soil. As the plants grow, the roots take in the insecticide from the soil. This helps control insects.

Granular insecticides used in cotton include acephate (Payload®), aldicarb (Temik®), disulfoton (Di-Syston®) and phorate (Thimet®). Most granular insecticides are highly toxic to wildlife, especially birds. Birds may eat exposed granules, mistaking them for food or grit. Swallowing just a few granules may kill a small bird.

Granules spilled at the ends of rows as applicator boxes are filled, or as equipment is raised, are particularly hazardous since birds often feed near field edges. The best way to reduce the hazard is to be sure granules are completely disked under and covered with soil. Recent "closed system" handling technology (Fig. 2) helps to eliminate spills of granules.

To reduce the risk of granular insecticides to wildlife:

• use the least toxic insecticide that will control the pest;

• completely cover granules with soil;

• disk turnrows after insecticide application; and

• use equipment designed to prevent spills.

Liquid Insecticides

Liquid formulations are usually sprayed on growing plants. Several are highly toxic to wildlife, including dicrotophos (Bidrin®), dimethoate (Cygon®, Dimate®), methomyl (Lannate®), methyl parathion and others. Minimize the risks of sprays by selecting the least toxic product that will control the target pest, especially when it is necessary to apply an insecticide more than once. Making multiple applications of insecticides increases the hazard. Wildlife that survives a single application may be more susceptible to repeated exposure. Therefore, it is very important to use the least toxic chemical possible.

A major concern when using a liquid spray is that the pesticide may drift from the crop field to other areas near by, and come in contact with wildlife. It is important to minimize drift by:

• using ground rigs rather than aerial applications, especially near sensitive habitats;

• using nozzles and spray pressures designed to produce large droplets;

• using a drift-control agent;

• not spraying when wind speeds are more than 8 to 10 mph;

• not spraying when the direction of the wind might carry the chemical away from the field to other areas;

• avoiding ultra-low volume sprays which produce small droplets; and

• checking for leaks, replacing worn parts and calibrating equipment carefully.

Do not apply pesticides if heavy rainfall is expected soon after application. Runoff from heavy rains can move pesticides into streams and ground water. Filter strips (see Herbicide section) can reduce pesticide movement from croplands to sensitive habitats such as wetlands.

When mixing pesticides, be certain to mix the correct concentration. Read and follow label directions carefully.

Using Fungicides Safely

Fungicides, used to control diseases, are only slightly toxic and most do not present a hazard to birds and mammals. However, some fungicides, including captan and PCNB (Terrachlor®), are highly toxic to fish.

Fungicide use can be reduced by controlling seedling diseases with cultural practices such as proper crop rotation and planting dates, and the selection of disease-resistant plant varieties.

Using Nematicides Safely

Nematicides are used to control nematodes, microscopic roundworms which are F parasites of plants. Commonly used nematicides such as aldicarb (Temik®) and fenamiphos (Nemacur®) are highly toxic and are known to have killed wildlife. Nematicide use can be reduced by rotating crops and applying chemicals only when nematode populations justify treatment. Granular nematicides should be disked under and completely covered with soil.

Integrated Pest Management

Reducing pesticide use is one of the best ways to protect wildlife. However, pesticide reduction must be coupled with good pest management practices so that crop yields and profits do not suffer. Integrated pest management (IPM) is the most effective method of accomplishing this objective. IPM is a system that monitors pest populations and uses biological, cultural and chemical controls to keep insect pests below economically damaging levels. In an IPM program, pesticides are used only after other tactics have failed to keep pest numbers or damage below levels which cause economic crop loss.

Cultural Controls

Cultural controls are especially effective in cotton production in Texas. The manipulation of planting dates on more than 1 million acres of cotton in the Rolling Plains helps manage the boll weevil and reduce the need for insecticide. Mandatory plowup dates on more than 500,000 acres of cotton in south and west Texas help control the boll weevil and\or pink bollworm.

Most cotton in Texas is grown in a short season production system. This means that varieties are selected for their ability to mature quickly, before insects can do severe damage. Decreasing the length of the growing season reduces the need for pesticides. Varieties that are resistant or tolerant to plant diseases and insects also should be used when available.

Crop rotation is another important cultural control which can be used to suppress certain disease and insect pests.

Biological Control

Increasing emphasis is being placed on biological control of cotton pests in Texas. Biological control is the use of natural enemies such as parasites, predators and pathogens to control insect pests. Biological control is most effective when used with cultural control practices in an integrated pest management program.

Conserving beneficial insects such as ladybeetles, green lacewings, damsel bugs and parasitic wasps is one component of IPM (Fig. 4). It is important to recognize beneficial insects in the field and know how they help control pests. Most insecticides kill beneficial as well as harmful insects, so they should be used only when necessary.

Another kind of biological control involves the use of biological insecticides, sometimes referred to as microbial insecticides. There are nearly 2,000 naturally occurring microorganisms, including bacteria, viruses, fungi, protozoa or their by-products, that could potentially help control major pests. The most commonly used biological insecticide is Bacillus thuringiensis, or Bt as it is usually called.

For more information on biological controls, refer to Extension publication B-5044,"Biological Control of Insect Pests in Wheat."

Endangered Species

Certain wildlife species are protected by state and/or federal laws under the Endangered Species Act. Texas currently has about 128 species (or subspecies) on its Threatened or Endangered Species list. Also, 28 species (or subspecies) of threatened and endangered plants are found within the state. Some wildlife populations may have declined because of the misuse of highly toxic and persistent pesticides, especially organochlorines such as DDT. Birds such as brown pelicans, bald eagles and peregrine falcons were particularly affected. Populations of these endangered birds have increased in recent years.

Two other species that are often mentioned on pesticide labels include the Attwater's prairie chicken and the Aplomado falcon, both residents of south Texas. These birds feed in or near croplands where pesticides are often used, and may be harmed by pesticide exposure. Aplomado falcons feed primarily on birds, some of which are migrants that may be exposed to illegal pesticides outside the U.S. The selective use of herbicides has helped prairie chickens by slowing the growth of brush on prime prairie chicken habitat.

There may be pesticide restrictions to protect endangered or threatened species in your area. Contact your county Extension office or the Texas Department of Agriculture to find out.

Interpreting Pesticide Poisoning

Most wildlife poisonings have involved either organophosphate or carbamate insecticides. Both of these chemical groups affect the nervous system; respiratory paralysis is the immediate cause of death. Animals can be exposed by swallowing or inhaling a chemical, or by getting it on the skin.

The clinical signs of pesticide poisoning vary with the particular chemical, but usually include respiratory distress, incoordination, tremors, paralysis and convulsions. Usually the animal either dies within a short time or recovers completely. Finding several sick and/or dead animals in an area within a short time is a sign of possible pesticide poisoning.

Birds appear to be the most susceptible terrestrial wildlife to insecticide poisoning. Waterfowl such as ducks and geese and passerine birds such as sparrows, blackbirds, robins, cowbirds and grackles have been the most common species involved in the poisoning incidents investigated.

According to a U.S. Fish and Wildlife Service report, the insecticides most often implicated in bird poisonings during the 1980s included the organophosphates diazinon, parathion, famphur and monocrotophos. In 18 incidents linked to carbamate insecticides, carbofuran was responsible for 16 cases.

Agricultural applications were implicated in about one-third of the die-offs investigated. Parathion has been the most common cause of pesticide related wildlife deaths in Texas. Most incidents involved geese feeding on wheat fields treated with parathion.

To Protect Fish and Wildlife

• Use IPM practices in your cotton production.

• Choose the pesticide least toxic to fish and wildlife.

• Protect field borders and other noncrop habitats from pesticide.

• Completely cover pesticide granules with soil, especially spilled granules at the ends of rows.

• Minimize chemical spray drift by using low-pressure sprays and nozzles that produce large droplets, and properly calibrating and maintaining spray equipment.

• Don't spray over ponds and drainage ditches.

• Never wash equipment or containers where rinse water could enter ponds or streams.

• Properly dispose of chemical containers.

• Read and follow pesticide label directions.

User Ethics

Every pesticide user has a legal duty to use the chemical according to label directions. Using pesticides contrary to label directions jeopardizes wildlife and exposes the user to criminal prosecution. It may ultimately result in further restrictions on pesticides. Please do your part to see that pesticides are used in a responsible fashion according to label directions.

Glossary

Biomagnification. The increase in the concentration of a chemical in organisms at eachhigher level of the food chain.

Direct effects. The adverse effects of coming into contact with a pesticide, specifically when an animal is exposed to a pesticide at a dose high enough to cause toxic effects. Dose. The amount of exposure an organism receives.

Exposure. Contact with a pesticide. Hazard. The inherent potential for a pesticide to harm fish or wildlife in a particular environment. A product of toxicity times exposure.

Indirect effects. When pesticide use decreases the quantity or quality of wildlife food supply or habitats.

Lethal dose 50 (LD₅₀). The amount of a chemical expressed as mg/kg of body weight) that kills 50 percent of a test group; this dose is often referred to as the "acute" toxicity of a pesticide.

Lethal concentration 50 (LC₅₀). The concentration of a chemical in the diet expressed as kg/mg of body weight) or in the aquatic environment of a species that kills 50 percent of the individuals over a specified period of time.

Persistence. The length of time a pesticide remains in the environment.

Pesticide formulation. The combination of a pesticide's active ingredient with solvents, carriers and other inert ingredients that form the pesticide product. Risk. The probability that the application of a pesticide will cause some harm.

Routes of exposure. The pathways by which wildlife are exposed to pesticides: skin contact, oral (through feeding, pruning, feeding and drinking) and inhalation.

Secondary poisoning. When a predator or scavenger becomes poisoned by feeding on contaminated prey.

Sublethal exposure. Exposure to a pesticide at levels that don't kill an animal but that may reduce its chance of survival or harm its ability to reproduce.

Toxicity. The capacity of a substance to harm a specific living organism.

This publication is one of a series on reducing risks of pesticides to wildlife. Others in the series are:

• "Reducing Pesticide Risks to Wildlife in Small Grains and Sorghum," B-5093.

• "Reducing Pesticide Risks to Wildlife on Rangeland," B-5096.

• "Reducing Pesticide Risks to Wildlife," B-5095.
  

For Additional Information

• "Pesticides and wildlife: a guide to reducing impacts on animals and their habitat." Virginia Department of Game and Inland Fisheries, publication 420-004.

• "Pesticide use and toxicology in relation to wildlife: organophosphorus and carbamate compounds." U.S. Fish and Wildlife Service, resource publication 170.

• "Wildlife and agricultural pesticide use: a review for natural resource managers." North Carolina Cooperative Extension Service, publication AG475.

• "Management of Cotton Insects." Texas Agricultural Extension Service, publications B-1204A, 1209A and 1210A.
  

• "Biological Control of Insect Pests in Wheat." Texas Agricultural Extension Service, publication B-5044.
  

• "Suggestions for Weed Control in Cotton." Texas Agricultural Extension Service, publication B-5039.
  

• "Minimizing Wildlife Risks from Agricultural Pesticides." Texas Agricultural Extension Service, video.
  

This publication was adapted from "Pesticides and Wildlife: Cotton," bulletin AG4634, published by theNorth Carolina Cooperative Extension Service and written by William E. Palmer and Peter T. Bromley, and also from "Pesticides and Wildlife - A Guide to Reducing Impacts on Animals and Their Habitat," published by Virginia Cooperative Extension and authored by Elizabeth R. Stinson and Peter T. Bromley. Gerrit Cuperus, Billy Higginbotham, Ron Howard, Allen Knutson and Roy Parker provided critical reviews of the text.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.

7.5M - 8-94, New
WM, CHEM 4

Return to top of page

Return to Departmental Home Page

Last modified: June 23, 1997 by Edgar Cross