Module 7 Chemical Control
- Explain the difference between anticoagulants and acute toxicants.
- Describe general application techniques for rodenticides and avicides.
- Explain the dangers of toxicants to non-target species.
Terms to Know
Acute toxicant A chemical that can cause severe illness or death with one feeding, generally within 24 hours.
Anticoagulant A toxicant that kills an animal by interfering with clotting of the blood. Death may result in several days after multiple feedings or for some anticoagulants, in several days after one feeding.
Chronic toxicant A chemical that requires multiple feedings before causing severe illness or death.
Fumigant A toxicant that is inhaled by a target species, causing illness or death.
Secondary poisoning When a predator or scavenger ingests a toxicant by eating an animal killed by that toxicant. Secondary poisoning causes sickness or death.
In this manual, “chemical control” means the use of pesticides, including repellents, to manage vertebrate pests.
Because of the risk to non-targets, this module focuses on toxicants, which include poisons and fumigants. In New York, any use of toxicants or repellents by NWCOs requires a pesticide applicator license. This applies to the use of commercial chemical pesticides as well as common household items such as moth balls and ammonia. If you are a NWCO using a product to kill or repel an animal, then you must have a pesticide applicator license. For more information on how to obtain a pesticide applicator license go to: http://www.dec.ny.gov/permits/209.html
Pesticide products currently registered for use in NYS are listed on the internet at the New York State Pesticide Administrator Database (NYSPAD) web site http://www.dec.ny.gov/nyspad/. Before using any product, you must check the database to see if the product is registered for use in NY and if the label states you can use the product for the target species. If a specific product is listed on that site, then it is currently registered for use in NYS. However, if the label states the product is registered for use on deer and rabbits, you can only use it on deer and rabbits. You cannot use that product on squirrels or chipmunks.
If, after checking the NYSPAD site, concerns remain about the registration status of a pesticide product, contact the NYSDEC Pesticide Product Registration Section at (518)-402-8768.
A repellent is a chemical that deters an animal pest from a specific location or from damaging activity. In most states, repellents are considered pesticides when used in commercial applications and must be applied by a certified applicator.
When used properly, chemical repellents are not toxic to target animals. The effectiveness of repellents often is highly variable, depending on the motivation of problem animals, alternative resources, previous experience, and active ingredients of the repellent. Repellents work best if alternative food and shelter are available to the pest and pest populations are low.
Repellents typically are sprayed on vegetation until it starts to drip off the leaves. Most repellents are available as liquid sprays, but some are available as granules, powders, and sachets. Repellents may have to be reapplied after rainfall or to protect new plant growth.
Chemical repellents come in
the following forms:
- Oral: A chemical that tastes unpleasant or even causes pain (e.g., spicy hot).
- Tactile: A chemical that feels unpleasant (e.g., gooey or sticky).
- Olfactory: A chemical that smells unpleasant or promotes fear of a natural predator (e.g., ammonia or rotten-egg odor).
Apply oral repellents to vegetation, seeds, or fruit. The bad taste of these chemicals may discourage birds, deer, and other pests. The effectiveness of oral repellents depends on the availability of other food. When food is scarce, repellents are less effective because the animal has few or no alternative foods. This means the animal is more likely to eat the high-value food in order to survive.
Capsaicin is an active ingredient responsible for the heat in peppers. When used as a repellent, it causes pain to animals that eat it.
Several oral repellents registered in NY contain the active ingredient anthraquinone, which causes gastrointestinal distress. When geese eat the treated vegetation, they vomit. The repellent changes the ultraviolet reflection of the grass where it is applied. After eating treated areas and becoming sick, when geese see the reflection, they may learn to avoid treated areas in the future. This active ingredient is registered in NY to repel gulls, geese, and several other species. It is available for a variety of sites including turf grass, ornamental plantings, agricultural sites and landfill areas.
Tactile repellents are most useful in keeping roosting birds away from buildings. You can apply most of them with caulk guns. Others are available as liquids, aerosols, nondrying films, and pastes. The mixtures work by making the birds’ feet uncomfortably sticky.
Improper or excessive application of tactile repellents may foul the feathers of non-target birds. It also can entrap birds on ledges or other sites. Dead birds that stick to ledges will decay and are difficult to remove. This not only violates label laws, but it can create a sanitation problem as well.
Apply sticky repellents about 1/2 inch thick in rows spaced no more than 3 to 4 inches apart. Increase or decrease row spacing depending on the size of the pest birds. Birds should not be able to land between the rows without contacting the repellent. Treat all roosting and loafing surfaces in a problem area or the birds will move a short distance to an untreated surface. When applying tactile repellents to buildings, clean the surfaces first. Then cover the surfaces with tape and apply the chemical to the tape. The tape will act as a barrier between the chemical and the surface. Otherwise, some materials may be difficult to remove or may stain the building.
Tactile repellents often become less sticky over time, especially in dusty areas. Usually, these materials will repel birds for less than one year before a second application is necessary. Always read the label for specific information and application instructions for each repellent used.
Olfactory repellents try to deter mammals through certain odors. Human hair, predator urine, soaps, and chemical-based rotten egg repellents sometimes have this effect. For example, coyote urine may cause herbivores to flee due to fear. Naphthalene (the active ingredient in mothballs) also may work to repel vertebrate pests. However, you may only use products containing naphthalene that are specifically registered for vertebrate control.
Toxicants are chemical compounds used to intentionally kill or impair target species. “Target species” refers to animals that are the target of management. “Non-target species” or “non-targets” refer to wildlife, livestock, pets, and people that are not the target of management and could be harmed by toxicants.
Toxicants can impact non-targets through primary exposure (direct ingestion of the toxicant), or secondary exposure (consumption of an animal that has eaten the toxicant). When misused, misapplied, or sometimes due to unfortunate circumstances, toxicants can pose a threat to non-target species. Safeguards are in place to minimize these risks, but in many cases, it is best to use reduced-risk alternatives to toxicants.
Toxicants can be beneficial and effective tools for controlling vertebrates such as house mice (Figure 1), Norway rats, pigeons, starlings, and house sparrows. Vertebrate toxicants can be applied in many forms and delivery methods to protect structures, turf, landscapes, cropland, rangeland, and other sites.
Public attitudes toward toxicants vary greatly. Some people have a “spray and pray” mentality, in which pesticides such as toxicants are the first and often only control method considered when confronted with a pest problem. Some pest management professionals rely too heavily on pesticides when alternative, reduced-risk approaches may be just as, or more, effective. Alternatively, some people are so opposed to the application of chemicals in the environment that they oppose all use of toxicants.
Opposition of this sort can be short-sighted in situations where damage is severe, human health concerns are high, and pesticides can be applied safely with minimal risk to the environment.
We recommend using toxicants as part of an integrated wildlife damage management (IWDM) program when other less hazardous options are not suitable or effective. The pest control industry uses the term Integrated Pest Management (IPM). Both approaches employ the timely use of a variety of cost-effective, environmentally safe, and socially acceptable methods to reduce human-wildlife conflicts to a tolerable level. Toxicants can be an important component in an IWDM strategy to reduce overall damage when implemented with other control methods, such as sanitation and exclusion.
Toxicants include a wide range of active ingredients that kill animals. Some are refined and concentrated forms of naturally occurring compounds (e.g., strychnine, warfarin, and carbon dioxide), while others are synthesized for lethal effects (e.g., phosphine, bromethalin, and brodifacoum). Toxicants have varying modes of action. Some reduce the ability of blood to clot (anticoagulants such as warfarin) while others affect the nervous system (bromethalin), metabolic processes (phosphine), and heart function (vitamin D3). Selection of the appropriate active ingredient depends on the target species, potential risks, previous methods used, application methods, and cost.
Toxicants are formulated to increase their effectiveness, attractiveness, and uptake by target animals. Baits include active ingredients and attractants (e.g., grains, fats, and flavor enhancers) that entice target animals to eat them. Baits are formulated into blocks, pastes, place packs, loose grains, and even plastic worms (Figure 2).
Bait blocks are the most commonly used formulation in the wildlife control industry because they are easy to use, are highly effective, and can be secured in bait boxes. Bait blocks come in several shapes, colors, flavors, and active ingredients that are appealing to different species.
Toxic tracking powders sometimes are used when ample food is in the area and rodents are unlikely to take formulated baits. Powders are applied in locations that are inaccessible to humans and where rodents frequently travel. The powder collects on the fur of the rodents and is ingested during normal grooming. Rodents may spread the toxic powder to other locations, so training and careful application are needed to reduce hazards to non-targets.
Liquid toxicants can be effective, especially when water is in short supply. Fumigants produce noxious gases that typically are delivered underground in burrows. Other toxicants are formulated to target canine predators (e.g., cyanide ejectors, livestock protection collars), and are registered for use in only a few states. Often, such applications are restricted to USDA-Wildlife Services professionals with specific training.
The registration and use of most toxicants is regulated by the US Environmental Protection Agency (EPA) through the authorization of the Federal Fungicide, Insecticide, and Rodenticide Act (FIFRA). Rules and regulations enforced by the EPA control the production, testing, labeling, transportation, storage, and application of all pesticides. Read the pesticide label for specific information on the target species, site of use, methods of application, hazards, and safety requirements. Use of a pesticide contrary to the label is illegal and punishable by federal and state laws. In addition, vertebrate pesticides are regulated by state departments of agriculture, human health, environmental conservation, and consumer protection. Some counties and local municipalities may have additional restrictions. Local and state regulations must be identical to or more restrictive than federal regulations. Check with your local agencies to ensure that you are in compliance with all regulations regarding the use of toxicants. Anyone using pesticides, including toxicants, in a commercial application must be a certified pesticide applicator, which requires coursework, examination, and state licensing.
In New York, persons who must be certified to apply pesticides to control vertebrate pests (Category 7A Vertebrate Pest Control certification) include 3 types of commercial applicators: applicators for hire, applicators not for hire, and government employees.
An example of a commercial applicator for hire who needs certification in Vertebrate Pest Control is an employee of a wildlife management firm that uses pesticides to control vertebrate pests for the public. A state park employee who uses a chemical to repel deer is an example of a government employee who needs certification in Vertebrate Pest Control.
Understanding Pesticide Labels
EPA-approved pesticide labels (Figure 3) are legal documents and contain important information. The label is the law. While only a few elements will be discussed here, always read the entire label before making an application. Complete understanding about the use, risks, and storage of toxicants is essential to effective and responsible use of pesticides. The rodenticide label in Figure 3 (next page) is laid out in three columns. We have identified eight sections of the label and will discuss each section in turn.
Section 1 provides the list of target species and site for which this rodenticide is approved. Use of the toxicant for species and site other than those listed is a violation of the label and the law.
Section 2 provides the amount of active ingredient and inert ingredients. The active ingredient is the chemical difethialone, which kills rodents. Inert ingredients are the grain and materials used to encourage rodents to feed on the bait.
Section 3 displays the human hazard signal word. Signal words, in order of highest to lowest hazard, are Danger, Warning, and Caution. First Strike® has the signal word Caution, the lowest hazard rating.
Section 4 contains safety information. Safety is of the utmost importance when applying toxicants. The pesticide label contains information that must be followed to use each product safely.
When applying toxicants, you must wear proper personal protective equipment (PPE). The required PPE will vary according to the active ingredient and formulation of the toxicant. First Strike® requires the standard PPE consisting of gloves (specifically waterproof gloves), a long-sleeved shirt, long-legged pants, shoes, and socks. Some pesticides may require additional safety equipment such as respirators, face shields, and protective suits.
Do not eat, drink, or smoke when applying pesticides. Check the pesticide label for detailed information before using any product. Always wash thoroughly after handling any pesticides (Figure 4). You may have residue on your hands, and could transfer that residue to equipment, food, other people, or other parts of your body.
Section 4 also contains instructions about what to do if a poisoning or other type of exposure occurs, such as to the eyes, skin, or clothing. With the social value of pets on the rise, and more recently in the courts, it is important to read the label recommendation for preventing poisoning of pets. The label tells how to prevent environmental hazards with the toxicant. Note the final line about protecting water quality. Always rinse items away from wells, drains, and streams. It is up to you to follow all of the safety requirements and recommendations.
Another good resource is the Safety Data Sheet (SDS). Manufacturers and distributors of pesticides must provide an SDS for each product that they sell. The SDS includes information about the product’s toxicity; how readily it dissolves in water; and if it is flammable, explosive, etc.
Section 5 explains how to store and dispose of the toxicant. First Strike® must be stored in a location that is cool, dry, and inaccessible to children. For some toxicants, the label will provide specific information on how the product must be transported, including where in the vehicle, and whether safety placards are required. Safe practices and equipment for handling and applying pesticides vary according to the active ingredient, formulation, and target species. Notification of pesticide application is an important element of pesticide safety. In many cases, proper notification is required regarding location and time of application so that clients and the public are aware of potential threats to health and safety. The safety of clients, non-target animals, and the public always must be primary factors when considering the use of toxicants.
Section 6 contains two sets of numbers that identify the pesticide and the manufacturer site respectively. “EPA Reg. No.” is an abbreviation for EPA Registration Number. First Strike® registration number is 7173-258. The 7173 represents the company LiphaTech, Inc., and the number 258 identifies the specific pesticide, First Strike®. The EPA Establishment Number or EPA Est. No. (7173-WI-1) identifies the specific manufacturing plant where the completed bait is produced. The 7173 identifies LiphaTech, Inc.; WI stands for Wisconsin; and the 1 identifies manufacturing plant 1. If a label has an EPA Registration No., it contains 3 sets of numbers, such as xxxx-xxxx-xxx, the last set of numbers identifies the distributor who has relabeled the pesticide to sell under another name. The numbers may be used to find research related to the product. Do an on-line search for “EPA Registration Number xxxxx-xxxx” to find out what is available.
Section 7 explains how to apply the product, including where it may and may not be used. The information in Section 7 and Section 1 must be combined to use the product properly. It states that you may apply the toxicant only where the label allows and for an appropriate target species.
Section 8, Use Restrictions, explains how NOT to use the product. First Strike® provides detailed information that limits how far from a building this bait may be used. Farther down the column, the amount of toxicant applied in a given area is limited. It explains that the maximum amount of bait you may use is four pouches every 12 feet when targeting house mice. The application rate is different for rats. The use of too little toxicant will result in reduced rodent control; the use of too much violates the law. If you ever have questions about the interpretation of a label, contact the agency in your state that regulates pesticides.
Toxicology is the study of chemical agents that kill animals. It is important to understand how toxicants work to maximize the efficiency of use on target species, and safety for non-targets. All pesticide labels give the percent active ingredient contained within the product (i.e., 2% zinc phosphide). The dose that an animal receives depends on how much is ingested and the weight of the animal, typically measured in milligrams per kilogram (mg/kg). The percentage of animals that die from an application of a toxicant varies depending on the active ingredient, dose, period of exposure, sex and age of the animal, and other factors.
The term “LD50” tells the level of toxicity of a chemical. “LD” means lethal dose. LD50 is the dose, based on weight, which will kill 50% of a population of test animals. Chemicals with lower LD50 values have greater toxicity because less of the active ingredient is needed to kill 50% of a population. An active ingredient such as strychnine, with an LD50 of 10 mg/kg in rats, is highly toxic and far more hazardous than an anticoagulant such as warfarin, which has an LD50 of 1,000 mg/kg in rats.
Avoid the use of highly toxic active ingredients in areas that are frequented by children, livestock, pets, and other non-target animals. Always read the pesticide label for safety information. The SDS (Safety Data Sheet) for the toxicant gives the LD50 and other information.
Rodenticides are classified by their modes of action. Most registered rodenticides are anticoagulants. When ingested, anticoagulants inhibit clotting of the blood. Animals die from stress-related internal bleeding or bleeding from external wounds. Rodenticides include first-generation products (e.g., warfarin), and more recently developed second-generation toxicants (e.g., brodifacoum, chlorophacinone, difethailone, and diphacinone). First-generation anticoagulants require multiple feedings to kill. While the effects of all anticoagulants are cumulative, causing chronic toxicity, some may be effective with a single dose. Keep fresh bait available continuously for at least 2 weeks, or until all feeding ceases.
Anticoagulant rodenticides seldom pose a hazard when they are consumed in a single feeding because the concentration of active ingredient typically is below 0.01%. A non-target animal usually must consume toxic bait several times to experience negative effects. In addition, Vitamin K1 can be used as an antidote to counteract the effects of anticoagulants. However, remember that any chemical, even one not used as a pesticide (table salt), may cause harm if enough is consumed.
The greatest risk when using toxic baits is poisoning non-target animals. The best way to reduce poisoning non-targets with rodenticide baits is to avoid using them where pets, livestock, children, and other non-targets are present. Apply baits only in tamper-resistant, locking bait boxes that prevent access by non-target species.
Anticoagulants do pose hazards for non-targets through secondary exposure (Figure 5). A rodent that has consumed an anticoagulant has concentrated levels of that compound in its body, especially in the liver, for several days. A predator or scavenger that eats poisoned rodents may receive a high dose of the toxicant. This can lead to impaired clotting of the blood and death. Brodifacoum and Diphacinone are toxic, particularly to dogs, and have relatively long biological half-lives.
Bait stations (Figure 6) have become the standard tool for applying rodenticides. Bait stations come in a variety of shapes and sizes, all of which are used to protect the bait, increase consumption of the bait by rodents, and minimize access to the bait by non-target animals. The rodenticide label may require the use of a bait station.
The following list outlines tactics to reduce hazards from anticoagulant rodenticide baits:
- avoid using where children, pets, livestock, and other non-targets are present;
- use the lowest hazard toxicant that will be effective (i.e., a high LD50), and apply toxicants in tamper-resistant bait boxes to minimize direct contact by non-targets;
- remove dead and impaired rodents found during daily inspections and follow proper sanitation practices; and
- use toxicants as part of an IWDM program, when other less hazardous methods have failed or will not meet management goals.
Some bait stations are large enough that bait and water can be placed inside. Place bait stations where rodents are active, especially where rodent signs (e.g., droppings, gnaw marks) occur along walls, under pallets, and behind equipment. Secure bait stations with screws, anchor bolts, or other fasteners. Use locks, seals, and concealed latches to make bait boxes tamper-resistant.
Check bait stations regularly to find out whether the target pests are using a station and to spot signs of trouble. If the pest does not take the bait, switch to another brand of bait or remove competing food sources. If some bait stations are working and others are not, relocate the ones that are not attracting pests.
Check bait stations daily if possible during the first week, and at least once per week thereafter, gradually reducing to monthly inspections. Refresh or replace bait as need.
In June 2011, the EPA implemented a Rodenticide Risk Mitigation Plan that is designed to reduce the risk of rodenticide exposure to children and non-target animals. The Plan restricts the use of second-generation anticoagulant rodenticides by the public and requires that all rodenticides be applied in bait stations. Certified pesticide applicators still can use second-generation anticoagulants, but amounts are restricted and some products have been removed from the market. For additional information, visit the website of the EPA at https://www.epa.gov/rodenticides
Besides anticoagulant (chronic toxicant) rodenticides, some are acute toxicants and have other modes of action. The concentration (%) of active ingredient in most formulations typically is much higher than in anticoagulant rodenticides. No antidotes exist for acute toxicants, so even greater care must be used during application. Acute toxicants, such as bromethalin, cholecalciferol, and zinc phosphide, can cause a quick reduction of a rodent population (often within a day), while anticoagulants typically reduce a population within 1 to 3 weeks. Quick-acting toxicants are useful when the risk of disease is high or when a very large population must be reduced in a short period of time.
Acute toxicants only should be used once or twice a year in the same locality to avoid the development of bait shyness in rodents. Bait shyness, when an animal avoids a bait, can occur when an animal eats a partial dose of a pesticide. This dose does not kill the animal but may produce side effects that could make the pest refuse the bait in the future.
Fewer toxicants are available for the control of birds than for the control of rodents. Only one toxic bait (DRC-1339, with the chemical 3-chloro-p-toluidine hydrochloride as active ingredient) and one frightening agent (Avitrol) are currently registered for birds in New York. In New York, DRC-1339 is available only to USDA-APHIS certified pesticide applicators or persons under their direct supervision for controlling starlings at livestock feedlots. Target birds must be pre-baited with untreated bait for at least three to four days or until the bait is being readily consumed. The treated bait then can be applied if no non-target birds are present. Birds that are treated typically die within one to three days from uremic poisoning. Sanitation and removal of dead birds are recommended, but the dead birds present no hazard through secondary exposure because the toxicant is metabolized by the dying birds.
Avoid leaving toxic baits exposed for long periods. The baits often become discolored, which may cause bait rejection. Another reason to avoid leaving toxic baits exposed for long periods is that they may endanger some protected bird species.
AvitrolTM is classified as a chemical frightening agent, although its active ingredient, 4-amino-pyridine, actually is toxic to birds. It is applied at a reduced dosage to disperse birds from an area rather than to kill them. The chemical is mixed in a ratio of 1 treated corn kernel to up to 99 untreated kernels. Target birds must be pre-baited for 3 days. When the bait is applied, treated kernels are ingested and causes distress response in affected birds, which may include distress calls, disorientation and erratic behavior. Overdose can cause tremors, convulsions and eventual death. Such behaviors frighten other birds from the area.
AvitrolTM should not be used as a pesticide to kill birds and is banned in cities with a population of one million or more in New York. You can minimize the impact to non-target animals when using avicides through the following:
- Pre-bait, with an ample supply. You are training the birds to come to the site. You cannot accomplish this if they can’t get enough to eat; they will go elsewhere to feed.
- Place toxic bait in a knowledgeable and timely fashion. For example, set out toxic bait before daybreak, otherwise birds may feed elsewhere before arriving at the bait site. Bait acceptance will be poorer, increasing the length of your control program.
- Remove and dispose of any dead birds and uneaten bait.
- Monitor animals feeding on the bait.
Other Vertebrate Toxicants
While only a few toxicants are available for the control of rodents and birds, even less are available for use on other species of vertebrates. Because of the benefits of wildlife, many regulations are in place to protect them. In addition, many vertebrate toxicants affect humans and other non-target species, so their use is not widespread.
Fumigants kill by means of toxic gas. For control of vertebrates, fumigants may be used in burrows or dens away from occupied structures.
Charcoal-based gas cartridges are general use pesticides (GUPs), available for purchase by the general public and are sold in 2 sizes, depending on the target species. They may pose a fire hazard. Below are general guidelines for placing and igniting a gas cartridge.
- Locate the main burrow opening and all secondary entrances.
- Cut a clump of sod slightly larger than each opening. Place a piece of sod over each entrance except the main entrance. Leave a precut sod clump next to the main entrance for later use.
- To prepare the gas cartridge for ignition and placement, follow the instructions on the label. Insert the fuse.
- Kneel at the burrow opening, light the fuse, and immediately place (do not throw) the cartridge as far down the hole as possible.
- Immediately close the main opening by placing the piece of precut sod, grass side down, over the opening. Make a tight seal with loose soil.
- Stand by for 3 to 4 minutes and watch nearby holes. Reseal any holes from which smoke is escaping.
- Repeat these steps until you have treated all burrow systems in the problem area.
Besides the gas cartridge, another type of fumigant is moisture-activated. An example is aluminum phosphide. This reacts with moisture to produce phosphine gas, which is extremely toxic to all mammals, including humans.
Fumigants with aluminum phosphide as the active ingredient are restricted use pesticides (RUPs), available for purchase and use only by certified applicators. Use extreme caution and pay close attention to label instructions when using fumigants. The use of aluminum phosphide has been more strictly regulated after the deaths of 2 children in Utah in 2010. The fumigant label listed an application rate of just two to four pellets per rodent burrow; it should not be used within 100 feet of homes or occupied structures. Investigators determined that the exterminator used a total of 1.5 lbs. of product in the yard to control voles and applied it seven feet from the front door of the home. A 15-month old and 4-year old died from inhaling toxic fumes, and the rest of the family was ill.
To reduce the risk of exposure when using a moisture-activated fumigant, an applicator should do the following:
- Open the container only in fresh air or near a fan or other ventilation system.
- When opening, point the container away from your face and body. Loosen the lid slowly.
- As with all pesticides, follow the label directions carefully. Wear all required PPE.
Seek training before using fumigants. You may need to have a fumigation management plan prior to use. Follow all label directions carefully; gas-cartridge fumigants pose a fire hazard, and moisture-activated fumigants produce an extremely toxic gas.
Few toxicants are available for use on wildlife, and their use is highly regulated and in nearly all cases you will need a pesticide applicators license. Nevertheless, toxicants often are a valuable tool in an overall integrated wildlife damage management approach, provided they are used responsibly, with consideration for non-target animals and the environment.
- US Environmental Protection Agency (http://www.epa.gov/pesticides),
- NYS Department of Environmental Conservation (http://dec.ny.gov)
- US Fish and Wildlife Service (http://www.fws.gov),
- University Extension Pesticide Safety Education Program