Acute Rodenticides

Alphachloralose

Alphachloralose is a moderately hazardous rodenticide. It is a narcotic and acts by slowing down the metabolism of the rodent. Death usually results from hypothermia. Alphachloralose is most effective at temperatures below about 15/16 degrees centigrade and is not recommended for use in centrally heated premises or areas where there is access to artificial heating.

Alphachloralose is not recommended for use against rats due to the larger size and reduced susceptibility to hypothermia, but can be used effectively against the House Mouse. Symptoms of poisoning occur in mice in about 5 – 10 minutes, with feeding ceasing after about 20 minutes. This can sometimes lead to sub lethal poisoning and possibly result in subsequent poison and bait shyness.

Alphachloralose is only suitable for indoor use by professional pest controllers.

Sub-Acute Rodenticides:

Warfarin

Warfarin is a first generation anticoagulant and indeed was the first of all the anticoagulants to be produced. The introduction of warfarin onto the market in the early 1950s revolutionised rodent control, enabling the achievement of complete eradication of rodent infestations (100% mortality) to become the expectation rather than the exception. Its arrival heralded the introduction of the other chronic multi-dose rodenticides and the technique known as saturation baiting. Warfarin remains a potent rodenticide although resistance, particularly in mice, has curtailed its effectiveness in some situations. Warfarin is suitable for both indoor and outdoor use by amateurs and professional pest controllers.

Coumatetralyl

Coumatetralyl, a first generation anticoagulant, was introduced into the European market in the late 1960s and early 1970s. Initial claims the coumatetralyl was effective against warfarin resistant populations of rats and mice were not fully substantiated in the field. Although a higher mortality was achieved against resistant populations, complete control was not obtained. Coumatetralyl is about as effective as warfarin against warfarin susceptible populations. Coumatetralyl can be used both indoors and outdoors by professional pest controllers.

Difenacoum

Difenacoum was the first of the second generation of anticoagulants and was introduced into the United Kingdom in 1974. It was discovered as a result of the search for alternative anticoagulants to overcome warfarin resistant rat and mouse infestations. Field trials in the early 1970s indicated that difenacoum was effective at eliminating warfarin resistant common rat populations and it also gave high levels of control against warfarin resistant populations of house mice. Some problems with palatability have been reported which seem to have been overcome in more recent years. Difenacoum should be applied using the saturation baiting technique. It can be used indoors and outdoors and is available for amateur use.

Bromadiolone

Bromadiolone is a second generation anticoagulant introduced into the United Kingdom market in about 1980. When introduced it was effective against first generation anticoagulant resistant populations of both rats and mice, although there was some suggestion that treatments against resistant house mice populations might need to be extended. Even with its higher rodent toxicity than many other anticoagulants, it is not considered sufficiently toxic to be used under a pulsed baiting regime and saturation baiting is recommended for this anticoagulant. It can be used both indoors and outdoors and is available for amateur use.

Brodifacoum

Brodifacoum, a second generation anticoagulant, introduced in the early 1980s, has perhaps the highest rodent toxicity of all the anticoagulant rodenticides. When introduced it was found to be effective against susceptible and first generation anticoagulant resistant rodent. Because of its higher toxicity and other characteristics, brodifacoum is able to deliver and acute LD50 dose through its consumption in bait of less than 10% of the average daily food intake of both rats and house mice. This high toxicity does not reduce the average time of death of the rodents nor does it reduce the average time taken to control an infestation. It does decrease the amount of bait that has to be consumed to ingest a lethal dose and potentially the number of days over which bait consumption takes place.

Brodifacoum is recommended as suitable for application using the pulsed baiting strategy. However, as a result of its higher non-target toxicity it is not cleared for use out of doors and may only be used by professional pest controllers. Brodifacoum can be used in sewers.

Flocoumafen

Flocoumafen is a second-generation anticoagulant and the most recent to appear on the united kingdom market. It has a very high toxicity to both rats and mice, although perhaps not quite as toxic as brodifacoum. Its high toxicity has enabled it to be sold as a single feed anticoagulant, in the same way as brodifacoum. Pulsed baiting is also recommended by the manufacturers, with the claimed advantages of reduced labour costs and use of bait.

Flocoumafen has been shown to be effective against populations of both rats and mice resistant to the first generation anticoagulants. Its toxicity to non-target species as well as rodents has resulted in a higher perceived environmental risk and flocoumafen is restricted to use indoors and in sewers only by professional pest controllers.