PROPERTIES OF VARIOUS POISONS USED TO CONTROL POSSUMS

Taken from NZ Toxicology Manual

Cyanide

Cyanide is used in New Zealand for killing possums but has limited use outside NZ. Because of its fast action cyanide is considered too dangerous for pest control in many countries. Cyanide containing compounds are found in some plants outside NZ as a defence against browsing animals. Cyanide is used for possum control in a paste form. Baits are handlaid and are small pea sized blobs that are used in conjunction with lured flour, cyanide kills very quickly and possums are generally recovered within a few meters of the baits. With prolonged use of cyanide possum populations can become poison shy and kill rates can become as low as 60% of the population.
A cyanide pellet is now available that is safer to use than standard pastes. The small coated pills can be useful where poison shyness is a problem and are used in baitstations with similar sized cereal feed pellets or with peanut butter. The main disadvantage with these pellets is the high cost and problems with rats removing pellets.

1080

History
Sodium monofluoroacetate was first used in the USA 50 years ago to control gophers, squirrels, prairie dogs, mice and rats. Manufactured 1080 for use in toxic baits has been shown to be chemically identical to the toxic compounds found in some poisonous plants. Research in the 1940s identified monofluoroacetate as the toxicant in the South African plant Gifblaar, long recognised as a hazard to livestock. Since then monofluoroacetate has been identified as the toxic agent in many other poisonous plants including 40 plant species in Australia. Monofluoroacetate also occurs at low levels in tea leaves and guar gum.

Mode of Action:
Sodium monofluoroacetate is non volatile and becomes poisonous when absorbed through the gastrointestinal tract and converted to the poison fluorocitrate which causes inhibition of energy production (krebbs cycle) which in turn results in cardiac or respiratory failure.

In the field 1080 is used in a pellet form. The pellets are 3–5 cm long, are cinnamon flavoured and dyed green to deter birds. Because 1080 breaks down quickly in rain the use of baitatations is the preferred method of application. The main advantage of 1080 over cyanide is the lack of toxic fumes and the fact that rats find 1080 pellets very palatable.

Brodifacoum

History
Brodifacoum is a synthetic compound developed 20 years ago. It is used in the product Talon, which is a very potent anti coagulant active against rats and mice. In New Zealand it is principally used to control rats and possums
Mode of action
Brodifacoum acts by interfering with the normal synthesis of vitamin K clotting factors in the liver. Poison symptoms often don’t appear for several days and in a sub lethal dose brodifacoum may persist in possum livers for at least 36 weeks. In the field brodifacoum is used in the form of a cereal pellet of similar size and colour as 1080. Larger amounts of brodifacoum are needed for possum control as rats can remove substantial   amounts of bait, which will not kill them for 5 or more days.

Single dose oral toxicity for various species (LD50mg/kg)

Cholecalciferol

History

Cholecalciferol was developed as a rodent poison in the US in the 1980s and was registered  in NZ in 1995 as a cereal bait possum poison. The active ingredient is Vitamin D3.  Campaign is only registered for use in baitstations  in NZ. The poisons works by releasing calcium from bones to the bloodstream causing mineralisation and blockage of blood vessels and death by heart failure. In possums it may take from 4 - 7 days for the poison to take effect.  Cholecalciferol is available in a cereal pellet, peanut butter paste and Gel form and can provide a good alternative to other poisons. The most common brand names are Decal and Feracol. At present Cholecalciferol is expensive and large amounts of poison may be needed where possum numbers are high. Prefeeding is crucial with cholecalciferol use as possums can become seriously poison shy if a sub lethal dose is ingested

LD50(mg/kg) for various species

Traps
Trapping is a valuable alternative possum control tool. Traps are used during prolonged spells of wet weather when poisoning becomes difficult and as a follow up to poison operations where poison shyness is suspected. The main types of traps used are: Victor / Bridger Double Spring leghold; Conibear killtrap and cage trap. Kill traps are useful where possums are wary of conventional leghold traps and cage traps are used near houses and public areas. See gallery for trap pictures. Nb where protected ground birds are present,  (eg Kiwi) traps are set on raised ramps

Safety Data Sheets: Cyanide  Decal

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