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.
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 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 other characteristics, 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 I 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.
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®).
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 be at least 30 feet wide, and preferably up to 100 feet, to make them useful to wildlife. Cost-sharing programs may be available for developing filter strips. Contact your local Soil Conservation Service office for details.
Insecticides are typically much more toxic to wildlife than herbicides. Insecticides commonly used in cotton are classified into five main groups:
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.
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 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 he 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 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:
A major concern when using a spray is that the pesticide may drift from the crop field to other areas nearby, and come in contact with wildlife. It is important to minimize drift by:
Pesticides also can move into streams or ponds when heavy rainfall causes runoff. Filter strips (see Herbicide section) can reduce pesticide movement from croplands to sensitive habitats such as wetlands.
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.
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.
Nematicides are used to control nematodes, microscopic roundworms which are 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.
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.
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 of 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.
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 posts. 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 Posts in Wheat."
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 he 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.
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 goose 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.
Every pesticide applicator has a legal duty to use the chemical according to label directions. Using pesticides contrary to label directions jeopardizes wildlife and exposes users 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.
Comments: Dr. Dale Rollins, Associate Professor and Extension Range Specialist, or