Dale Rollins, Thomas W. Fuchs, and Judy Winn
How Wildlife Are at Risk | Types of Insecticides | Using Insecticides Safely | Fungicides | Herbicides | Integrated Pest Management | Endangered Species | Interpreting Pesticide Poisoning | User Ethics | To Protect Fish and Wildlife Resources
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.
Pesticides are an integral part of modern farming practices. The proper use of pesticides helps ensure that Americans have an abundant, safe and inexpensive food supply. Pesticides improve crop yields and quality, and help to make farming practices profitable. Sometimes, however, pesticides can threaten wildlife and wildlife habitat.
Small grains such as wheat and sorghum provide food and cover for many wildlife species. Doves, quail, and other birds eat seeds of grain crops after they are planted and after the plants have produced grain. Many birds feed on insects found in grain fields. Mammals such as rabbits and deer eat the foliage of small grains throughout the winter and spring. Therefore, wildlife may be at risk unless pesticides are used properly.
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 pesticides. Wildlife that are in fields when pesticides are applied, or that enter fields shortly afterward, may inhale vapors or get insecticides 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 rain into streams, ponds, or other wetlands can harm aquatic animals.
Types of Insecticides
Four types of insecticides are used on grain crops:
- carbamates; and
- synthetic pyrethroids
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. Lindane is the only organochlorine insecticide labelled for use in small grains or sorghum in Texas, and it is used only as a seed treatment.
Organophosphate insecticides are widely used. This group includes chlorpyrifos (Lorsban®), dimethoate (Cygon®, Dimate®), disulfoton (Di-Syston®), malathion, parathion, and terbufos (Counter®). The toxicity of organophosphates ranges from low (malathion) to high (parathion).
Carbamate insecticides also are commonly used. These include carbaryl (Sevin®), carbofuran (Furadan®), and methomyl (Lannate®). Some carbamate compounds such as carbaryl are not very toxic to terrestrial wildlife (specifically birds), while others such as carbofuran and methomyl are highly toxic.
Synthetic pyrethroid insecticides generally have low toxicity to birds and mammals. However, they are extremely toxic to fish and other aquatic life. With the possible exception of esfenvalerate (Asana XL®) on grain sorghum, synthetic pyrethroids are not often used on small grains or sorghum.
Pesticides can be applied as sprays, granules, dusts, seed treatments or baits. Spray and granular formulations are most common in small grain and sorghum production. Sprays are typically applied after plants are growing, while granular formulations are generally applied at planting time. See Table 1 for a list of insecticides and their toxicities to certain wildlife species.
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 insecticide can cause sickness and death. Sublethal doses (doses not large enough to kill an animal) may make an animal sick or 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. Sublethal doses also may make animals more vulnerable to predators.
The effects of insecticides on wildlife and fish can be determined by using the least toxic chemical. An insecticide’s hazard to wildlife is based on several factors, including its toxicity to wildlife, 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 Table 1, insecticides with a rating of “High” may cause wildlife to die or become sick; a “Moderate” rating means an insecticide 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 animals.
Using Insecticides Safely
Granular formulations of insecticides are often used at planting time. The granules are dropped into the seed furrow and covered with soil. As the plants grow, the roots take in insecticide from the surrounding soil. Granular formulations now labelled for use in small grains or sorghum are aldicarb (Temik®), chlorpyrifos (Lorsban®), phorate (Rampart®, Thimet®) and terbufos (Counter®).
Granular insecticides pose a special threat to birds that feed in fields during planting time. They may swallow the granules accidentally, or mistake them for seeds or grit, and become poisoned. Just a few granules can be enough to kill a bird the size of a sparrow. Whenever granular insecticides are used, the hazard to wildlife can be reduced by completely covering the granules with soil. Be especially careful to disk under granules spilled at row ends where birds are likely to search for food. Be careful not to spill granules while loading them in the hoppers on your planting equipment. If a spill occurs, cover granules with soil. New “closed system” handling technology helps to eliminate spills.
Liquid formulations are usually sprayed on growing plants. The danger to wildlife from liquid insecticides depends mainly on the particular chemical’s toxicity. Methyl parathion, disulfoton (Di-syston®) and dimethoate (Cygon®, Dimethoate®) are highly toxic to wildlife and have been documented to cause wildlife kills. Methomyl (Lannate®) is also highly toxic to wildlife, but has not been reported to cause wildlife deaths when applied according to the label. Carbaryl (Sevin®) and malathion are less toxic to wildlife. Esfenvalerate (Asana XL®) is relatively safe for terrestrial wildlife, but should not be used near ponds or other wetlands.
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:
- using ground rigs rather than aerial applications when appropriate, especially near sensitive habitats;
- using nozzles and spray pressures designed to produce large droplet size;
- 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; and
- avoiding ultra-low-volume sprays which produce small droplets.
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.
Fungicides used in small grain and sorghum fields include foliar sprays and seed treatments. Quail and other seed-eating birds may be exposed to fungicides by eating treated seeds shortly after planting. Fungicides currently used on small grains and sorghum have a low toxicity to birds and mammals and do not present a hazard to wildlife. However, some fungicides such as mancozeb (Dithane M-45®, Penncozeb®, Manzate 20®) are toxic to fish. Triadimefon (Bayleton®) and propiconazole (Tilt®) are only moderately to slightly toxic to fish. Fungicide use can be reduced by controlling diseases with cultural practices such as crop rotations, timely planting and variety selection.
About 70 percent of the pesticides used in the U.S. are herbicides. With the exception or paraquat (Gramoxone Extra®, Cyclone®), most herbicides used for small grains or sorghum are only slightly toxic to wildlife (Table 2). The greatest risk to wildlife from herbicides is the effect they may have on wildlife habitat.
Many species of wildlife benefit from the seeds or other food produced in and around small grain and sorghum fields. Wildlife rely on the trees, brush, grass, and weeds near fields for food and cover. Fencerows, turnrows, borrow ditches, field borders, and shelterbelts are important habitats for gamebirds such as quail and pheasants, 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 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 for details.
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 all available tactics such as 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 the level that causes economic crop loss.
Biological control is the use of natural enemies such as parasites, predators and pathogens to control pests. Biological control is most effective when used with other compatible pest control practices in an IPM program. These practices include cultural controls such as rotating crops and planting pest-resistant varieties.
Conserving beneficial insects such as ladybeetles, green lacewings, damsel bugs and parasitic wasps is one part of IPM. 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 pesticides, sometimes referred to as microbial pesticides. There are nearly 2,000 naturally occurring microorganisms, including bacteria, viruses, fungi, or protozoa or their by-products, that could potentially help control major pests. The most commonly used biological insecticide today 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.”
Certain wildlife species are protected by state and/or federal laws under the Endangered Species Act. Texas currently has about 128 species (or subspecies) of animals on its Threatened or Endangered Species list. Also, 28 species (or subspecies) of animals on its threatened and endangered plants are found within the state. The misuse of persistent pesticides, especially organochlorines such as DDT, contributed to the decline of birds such as brown pelicans, bald eagles, and peregrine falcons. Populations of these endangered birds have increased in recent years since persistent pesticides were removed from the market.
Two other species that are often mentioned on pesticide labels are 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 within your county to protect endangered or threatened species. Contact your county Extension office or the Texas Department of Agriculture for restrictions that may apply in your area.
Interpreting Pesticide Poisoning
Most wildlife poisonings in Texas 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 or feathers.
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 and starlings, 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 includes the organophosphates diazinon, parathion 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.
To Protect Fish and Wildlife Resources
- Use IPM practices in your grain production
- Choose the pesticide least toxic to fish and wildlife that will control the target pest.
- Protect field borders and other noncrop habitats from pesticide applications.
- Never spray leftover pesticides into wildlife habitats.
- Completely cover pesticide granules with soil, especially spilled granules at the ends of rows.
- Minimize chemical drift by using low-pressure sprays and nozzles that produce large droplets.
- Protect wetlands from spraying and don’t spray over ponds or drainage ditches.
- Never wash spray equipment or containers where rinse water could enter ponds or streams.
- Properly dispose of chemical containers.
- Read and follow the instructions on the pesticide label.
|Pesticide||Brand Name||Chemical Groupa||Hazard rating for:||Wildlife Killsd|
|aOP – organophosphate CB – carbamate
OC – organochlorine SP – synthetic pyrethroid
bWildlife hazard is based on the following toxicities:
H (Highly toxic) – LD50 less than 30 mg/kg and LC50 less than 500 ppm
M (Moderately toxic) – LD50 between 30 and 100 mg/kg and/or LC50 greater than 500 and less than 1,000 ppm
L (Low toxicity) – LD50 greater than 100 mg/kg and LC50 greater than 1,000 ppm
cFish hazard based on the following 96-hour LC50 toxicities:
EH (Extremely toxic) – less than 0.1 ppm M (Moderately toxic) – 1 to 10 ppm
H (Highly toxic) – 0.1 to 1.0 ppm L (Low toxicity) – greater than 10 ppm
Yes – indicates wildlife deaths due to use of insecticide (active ingredient) have been reported
No – indicates wildlife deaths have not been reported when insecticide is used according to label
|Herbicide||Brand name||Hazard rating for:|
|paraquat||Gramoxone Extra®, Cyclone®||M||M-H||L|
|aWildlife hazard is based on the following toxicities:
H (Highly toxic) – LD50 less than 30 mg/kg and LC50 less than 500 ppm.
M (Moderately toxic) – LD50 between 30 and 100 mg/kg and/or LC50 greater than 500 and less than 1,000 ppm.
L (Low toxicity) – LD50 greater than 100 mg/kg and LC50 greater than 1,000 ppm
bFish hazard based on the following 96-hour LC50 toxicities
EH (Extremely toxic) – less than 0.1 ppm
H (Highly toxic) – 0.1 to 1.0 ppm.
M (Moderately toxic) – 1 to 10 ppm