Repellents and Toxicants

Prepared by the National Wildlife Control Training Program.
 Research-based, certified wildlife control training programs to solve human – wildlife conflicts.

Module 7      Repellents and Toxicants

Learning Objectives

Module 7 addresses many of the issues and concerns regarding repellents and toxicants that are used when dealing with human-wildlife conflicts.

  1. Explain the difference between anticoagulants and acute toxicants.
  2. Describe general application techniques for rodenticides.
  3. Give an example of the dangers of toxicants to non-target species.


Public attitudes toward chemicals such as repellents and toxicants vary greatly. Some people have a “spray and pray” mentality, in which pesticides are the first, and often only control method considered when confronted with a pest problem. Alternatively, some people are so opposed to the application of chemicals in the environment that they oppose all use of repellents and toxicants.

Integrated pest management (IPM) seeks to use effective, selective, and humane techniques to reduce damage to tolerable levels. We recommend considering the use of repellents and toxicants as part of an integrated approach to wildlife damage management (WDM). Pesticides may be an important component for reducing wildlife damage when used with other control methods, such as sanitation and exclusion.


The US Environmental Protection Agency (EPA) is the federal agency responsible for regulating pesticides. A pesticide is any substance, or mixture of substances, intended for preventing, destroying, repelling, or mitigating any pest problem, including plants.

Repellents – pesticides used to deter animal activity while not causing permanent harm or injury.

Toxicants – chemical compounds used to intentionally kill or impair target species.

Target species – management activities are directed at these specific animals.

Non-target species or non-targets – wildlife, livestock, pets, and people which could be negatively impacted by a pesticide application. When misused, misapplied, or sometimes just due to unfortunate circumstances, toxicants can pose a threat to non-target species. Safeguards are available to minimize these risks, but in some cases, it is best to use reduced-risk alternatives to toxicants.

Primary exposure – the effects on an animal that has directly encountered the pesticide. A mouse that died due to ingestion of a rodenticide is an example of primary exposure.

Secondary exposure -the effects on an individual that has eaten an animal with primary exposure. An owl that ate a poisoned mouse is an example of secondary exposure.

Active ingredients – specific chemical compounds that produce the desired outcome in the target species. Repellents and toxicants include a wide range of active ingredients. Some are refined and concentrated forms of naturally-occurring compounds (capsaicin, blood, urine, strychnine, warfarin, and carbon dioxide), while others are synthesized for the desired effects (phosphine, bromethalin, and brodifacoum).

Formulation – the way the active ingredient is packaged for delivery to the intended target species. Pesticides are formulated to increase their effectiveness, attractiveness, and uptake by target animals.

For example, bait formulations include active ingredients and attractants (e.g., grains, fats, and flavor enhancers) that entice target animals to eat them. Baits may be formulated into blocks, pastes, place packs, and loose grains (Figure 1). Bait blocks are the most common formulation for the control of rats and mice that live in close association with people. Bait blocks are easy to use, 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.

7_1_Block_Pellet_Meal_Formulations Rodenticide
Figure 1. Clockwise from top. Block, pellet, and meal formulations of a rodenticide. 


The registration and use of most pesticides is regulated by the 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.

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 pesticide regulations. Anyone using pesticides in a commercial application must be a certified pesticide applicator, which requires coursework, examination, and state licensing.

The EPA classifies some pesticides as Restricted Use Pesticides (RUPs). RUPs are available only to people with a certified applicators license. Those not classified as RUPs are considered General Use Pesticides (GUPs) and may be purchased over the counter. Many GUPs have the same active ingredients used in RUPs. The difference is that GUPs present less risk to people and the environment. They generally have lower concentrations of the active ingredient, are sold only in small quantities (1 pound or less), or in formulations, such as wax blocks or soft baits that present lower risk to non-targets because rodents cannot move the toxicant easily.

In general, services of a certified pesticide applicator are required whenever a person wishes to apply pesticides commercially, or on someone else’s property.

Prior to purchasing and using a pesticide, read the 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.


Repellents are classified by their mode of action – pain, fear, touch, or aversive conditioning.

Active ingredients used to repel animals by pain include capsaicin and methyl anthranilate, which are irritants for mammals and birds, respectively. An animal must taste or inhale the repellent for it to be effective.

Active ingredients that use fear to repel animals include putrescent whole egg solids and coyote urine. Fear-based repellents are designed to make target animals think a predator is nearby and thereby avoid the location.

Repellents based on touch include polybutene-based caulks. Their stickiness makes animals avoid treated locations (Figure 2). Because polybutene-based caulks trap dust and may stain surfaces, they should only be used on properly-treated areas for short-term relief. Such repellent caulks are usually applied indoors.

Figure 2. Two brands of polybutene-based caulks used to deter wildlife. 

Finally, repellents using aversive conditioning are quite different in that the reaction of target animals is delayed. Animals first consume the product, and in a few hours feel sick. They associate the illness with the food or area where they fed. This mode of action is used by the goose repellent Flight Control™. Geese that consume turf sprayed with anthraquinone quickly learn that treated grass causes nausea, and avoid eating treated grass in the future.

The effectiveness of repellents varies considerably depending on the motivation of problem animals, alternative foods, previous experience, and active ingredients of the repellent. Repellents often fail to deter animals, and it is rare for repellents to consistently end wildlife conflicts. Consequently, landowners must learn to tolerate some damage when using repellents. Read labels carefully before application, as some repellents cannot be used on plants destined for livestock or human consumption.


Toxicants can be beneficial and cost-effective tools for controlling vertebrates, such as house mice and Norway rats (Figure 3). Vertebrate pesticides can be applied in many formulations and using delivery methods to protect structures, turf, landscapes, cropland, rangeland, and other sites.  There are some toxicants available for unprotected birds (e.g., European starlings and pigeons), but these are registered for use only by certified applicators trained in bird control.

Figure 3. Toxicants in the form of bait blocks with bait stations are used to control house mice and Norway rats.

As with repellents, toxicants have varying modes of action. Some reduce the ability of blood to clot (anticoagulants, such as warfarin), and 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 that entice target animals to eat them.

Pesticide Labels

The EPA is responsible for registering pesticides. Pesticide labels are legal documents and contain information that will reduce the risk of harming people or the environment (Figure 5). While only a few elements will be discussed here, always read the entire label before making an application. Complete understanding of the use, risks, and storage is essential to the effective and responsible use of pesticides. In addition, the label is the law. Below are 8 sections of a rodenticide label (Figure 4) that require further consideration.

Section 1 provides the list of target species for which this rodenticide is approved. Use of the toxicant for species other than those listed is a violation of the label and the law.

Section 2 provides the amount of active ingredient and inert ingredients contained in this formulation of the toxicant. 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. Signal words, in descending order of 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 utmost importance when applying toxicants. The pesticide label contains the minimum requirements to safely use each product. This section  also contains information on what to do if someone ingests the toxicant, or other types of exposure occurs, such as to the eyes, skin, or clothing.

Harm to people is not the only concern. Pets are extremely valuable to their owners and the illness or death of a pet could result in a lawsuit. The label explains how to prevent harm to pets and non-target wildlife, in addition to the environment. For many pesticides, proper use is vital to protect water quality. The label will give instructions such as “Always rinse items away from wells, drains, and streams.” It is up to you to follow all of the safety requirements and recommendations.

Wear the proper personal protective equipment (PPE) when applying pesticides. The required PPE will vary according to the active ingredient and formulation of the toxicant. First Strike®requires standard PPE consisting of gloves (specifically waterproof gloves), a long-sleeved shirt, long pants, shoes, and socks.

Do not eat, drink, or smoke when applying pesticides. Some pesticides may require additional safety equipment, such as respirators, face shields, and protective suits. Check the pesticide label for detailed information before using any product. Always wash thoroughly after handling any pesticide (Figure 4).

Figure 4. Always wash after handling pesticides.


Figure 5. Sample EPA label for a rodent toxicant containing the active ingredient difethialone. 

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 placement 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 2 sets of numbers that identify the pesticide and the manufacturer site, respectively. “EPA Reg. No.” is an abbreviation for EPA Registration Number. The First Strike® registration number is 7173-258. It identifies the product and company that produced it. The EPA Est. No. or EPA Establishment Number identifies the specific manufacturing plant where the completed bait is produced. You can use these numbers to find research related to the product. Type “EPA Registration Number xxxxx-xxxx” into an on-line search engine 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 properly use the product. It states that you may apply the toxicant only where the label allows, and for the appropriate target species.

Section 8 explains how NOT to use the product. First Strike® provides detailed information that limits how far from a building this bait may be used. Further 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 4 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, and 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 their efficiency on target species, and safety for non-targets. All pesticide labels indicate the percent active ingredient contained within the product (e.g., 2% zinc phosphide). The percentage of animals that die from an application of a toxicant varies depending on the active ingredient, amount ingested, weight of the animal, period of exposure, sex and age of the animal, and other factors.

The toxicity of a pesticide is measured by its LD50 (lethal dose, 50 percent). This describes the dose of a pesticide that will kill half of a group of test animals (rats, mice, or rabbits) from a single exposure or dose by absorption through the skin, ingestion, or inhalation. The LD50 is given as the dose per unit of body weight, such as milligrams per kilogram (mg/kg). A pesticide with a lower LD50 is more toxic than a pesticide with a higher number because it takes less of the pesticide to kill half of the test animals. 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 livestock, pets, children, and other non-target animals. Always read the pesticide label for safety information.


Rodenticides are classified by their modes of action. The majority of registered rodenticides are anticoagulants. When ingested, anticoagulants inhibit blood clotting. Animals die from internal bleeding (caused by stress), or bleeding from external wounds. While the effects of all anticoagulants are cumulative, some may be effective with a single dose. Active ingredients include first-generation rodenticides (multiple-dose rodenticides such as warfarin), and more recently developed second-generation rodenticides (single-dose rodenticides including brodifacoum, chlorophacinone, difethailone, and diphacinone). Keep fresh bait available continuously for at least 2 weeks, or until all feeding ceases.

Due to the low amounts of active ingredients, anticoagulant rodenticides seldom are primary hazards. Non-target animals have to consume a considerable amount of anticoagulant bait to experience immediate negative effects. In addition, vitamin K1 can be used as an antidote to counteract the effects of most anticoagulants. Nevertheless, no pesticide is “safe,” and it is illegal to make such a claim regarding pesticides.

The best way to reduce primary hazards 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. If not applied correctly, non-target animals are at risk. Animals that die from anticoagulant exposure often show signs of bleeding near their mouth or anus (Figure 6).

Anticoagulants may pose secondary hazards for non-target animals. A rodent that has eaten an anticoagulant has concentrated levels of that compound in its body (especially in the liver) for several days. A predator or scavenger that consumes intoxicated rodents may receive a high dose of the toxicant, which in turn can lead to impaired clotting of their blood and death. Brodifacoum and diphacinone are particularly toxic to dogs, and have relatively long biological half-lives. Half-life refers to the amount of time needed for the body to excrete or process ½ of the active ingredient from the body.

Figure 6. An opossum shows the effects of poisoning by anticoagulants. 

The following list outlines tactics to reduce hazards from anticoagulant rodenticide baits.

  1. Avoid using them where pets, livestock, children, and other non-targets are present.
  2. Use the toxicant with the lowest hazard (i.e., a high LD50) that will still be effective.
  3. Apply toxicants in tamper-resistant bait boxes designed to protect bait against weather and access by children and other non-targets (i.e., EPA bait station Type IV).
  4. Remove dead and impaired rodents found during daily inspections.
  5. Use toxicants as part of an integrated WDM program, when other less hazardous methods have failed, or will not meet management goals.

Bait Stations

Bait stations (Figure 7) are the most common way to apply 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.

Figure 7. Bait stations for rodents. Block placement is shown. The metal wire (lower right) is the key to unlock the bait station. 

As part of EPA’s new risk mitigation for rodenticides, all rodenticide bait products marketed to residential consumers must be sold with, and used in protective, tamper resistant bait stations (bait boxes). These increase both the effectiveness and safety of rodenticides.

Bait stations are useful because they:

  1. protect bait from moisture and dust,
  2. provide a protected place for rodents to feed,
  3. keep non-target animals and children away from hazardous bait,
  4. allow placement of baits in locations where it otherwise would be difficult because of weather or potential hazards to non-targets, and
  5. prevent accidental spilling of bait.

Some bait stations are large enough that bait and water can be placed inside. Place bait stations where rodents are active, especially where there are signs such as fresh droppings and gnaw marks 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 stations regularly, daily if possible, during the first week, and at least once per week thereafter. Gradually reduce to monthly inspections, and refresh or replace bait as need.

Other rodenticides are acute (i.e., quick acting) toxicants and have other modes of action. The concentration of active ingredient (usually percentage by weight) 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 may cause the 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 disease hazard is high, or when a very large population must be reduced in a short period of time. Only use an acute toxicant once or twice per year in the same locality to avoid the development of bait shyness in rodents.


Fewer toxicants are available for bird control than for rodents. Starlicide Complete™ (p-n2-toluene) is available to certified pesticide applicators for controlling starlings at livestock feedlots.

AvitrolTM (4-amino-pyridine) is a restricted-use product classified as a chemical frightening agent (repellent). It is applied to disperse birds rather than kill them. The chemical is mixed in a ratio of 1 treated corn kernel to 99 untreated kernels. When the bait is ingested, affected birds have convulsions, exhibit erratic behavior, and they die. In doing so, they frighten other birds from the area.

Fertility control agents are considered pesticides and must be applied by a certified applicator. Products used to reduce egg hatchability (e.g., OvocontrolTM, active ingredient nicarbazin) are pesticides and registered by the EPA. In some states, even food-grade corn oil is considered a pesticide when applied to eggs to reduce hatchability. State pesticide regulations vary considerably. Anyone who makes a commercial application must be licensed and know state laws and regulations.

Other Vertebrate Pesticides

While only a few toxicants are available for the control of rodents and birds, even less are available for use on other vertebrate species. Wildlife is beneficial and many regulations are in place to protect wildlife. In addition, many vertebrate pesticides affect humans and other non-target species, so their use is not widespread.

Diphacinone and warfarin are registered for mole control in turf. They are formulated as plastic worms or gels, and can be applied only in underground tunnels that are frequented by moles.


Fumigants kill animals via toxic gas. Fumigants typically are used in burrows or dens away from human structures for mammal control. Charcoal-based gas cartridges are GUPs, and may be used for woodchucks.

Fumigants with aluminum phosphide as the active ingredient are RUPs, and available only to certified applicators. Aluminum phosphide is extremely toxic and its use has been more strictly regulated since the deaths of 2 children in Utah in 2010. Fumigants carry multiple primary hazards, including risk of fire. Find out if you must be a certified applicator to apply a particular fumigant, and if a Fumigation Management Plan must be developed prior to use. Seek training before using fumigants.


Relatively few toxicants are available for use on vertebrate pests and their use is highly regulated by federal and state agencies. Nevertheless, pesticides may be a valuable tool in an overall IPM strategy, provided they are used responsibly.

Additional Resources

Contact the following agencies or organizations for additional information.

  • US Environmental Protection Agency (
  • US Fish and Wildlife Service (
  • University Extension Pesticide Safety Education Program
  • State Department of Agriculture, Office of Pesticide Programs
  • State Department of Wildlife or Environmental Conservation

 Questions for Reflection

  1. A client is concerned about the risk of using an anticoagulant rodenticide near her dog. How would you respond?
  2. What are some ways you can reduce the risk of toxicants to non-target animals?
  3. Why is it important to wash your hands after every rodenticide application?
  4. Provide an example of when a pesticide is not considered a toxicant.
  5. Explain the difference between primary and secondary pesticide exposure.