There are three types, or groups, of rodenticides:

1. Acute poisons
2. First-generation anticoagulant rodenticides
3. Second-generation anticoagulant rodenticides.

Acute poisons

Acute poisons, as their name suggests, are fast-acting, single-dose toxicants that produce symptoms in rodents very rapidly. While these properties makes them highly effective exterminating agents, rodent behaviour is such that individuals encountering new food for the first time will test it, and not take a substantial quantity for hours, or even days (Buckle et al., 1987). Because rodents are neophobic, they can rapidly develop bait avoidance towards acute poisons, thereby jeopardising a key component of an on-farm rodent control strategy. This is why these compounds are generally most effective when used in short rotation.

Acute poisons AVPMA-registered rodenticides are:

• Cholecalciferol, also known as Vitamin D₃ or activated 7-dehydricholesterol
• Zinc phosphide.

First-generation anticoagulant rodenticides

Anticoagulant rodenticides (ARs), originally developed for therapeutic treatment of blood clots, can counteract the neophobic behaviour of rodents because of a considerable delay between consumption of bait and the emergence of symptoms. Early commercial examples of these compounds are known as first-generation ARs. They dominated rodent control in the 1950s and 1960s. However, heavy use of these compounds led to resistant rodent strains (Rowe and Redfern, 1965; Greaves and Ayres, 1969; Hadler and Shadbolt, 1975; Thijson, 1995). First-generation ARs are still available, but their use has declined in favour of more potent compounds, known as second-generation ARs.

First-generation anticoagulant AVPMA-registered rodenticides are:

• Coumatetralyl
• Diphacinone
• Warfarin.

Second-generation anticoagulant rodenticides

First-generation ARs dominated rodent control in the 1950s and 1960s. However, heavy use led to resistant rodent strains (Rowe and Redfern, 1965; Greaves and Ayres, 1969; Hadler and Shadbolt, 1975; Thijson, 1995), stimulating the development of second-generation of anticoagulant rodenticides (SGARs), which have a much greater potency and longer half-lives in animal tissue. SGARs are effective at controlling previously resistant strains while maintaining the delayed onset of symptoms required to prevent bait avoidance. However, because of the greater potency and persistence of these compounds in the tissues of baited rodents, they have a higher secondary poisoning risk. Livestock- and food-producing industries, in particular, need to take great care to prevent contaminating production areas from the SGAR bait itself and SGAR-baited rodents.

Second-generation anticoagulant AVPMA-registered rodenticides are:

• Brodifacoum
• Bromadiolone
• Difenacoum
• Difethialone
• Flocoumafen.

Detailed information about each of these rodenticides is provided in Active compounds in different rodenticides, including their:

• Development and use
• Mode of action
• Time to death
• Evidence of resistance
• APVMA-registered products containing this compound
• Available formulations
• Poison schedule and regulatory requirements
• Handling, storage and user safety.