Charlie Eason

Possums are responsible for major damage to native forests in New Zealand and several baits are available to control this pest. However, there are no data on the persistence of the toxicants in these baits during periods of rain. Four commonly used possum cereal baits were exposed to simulated rainfall to investigate weathering of bait, persistence of toxicant in the bait, and the rate of leaching and persistence of toxicant in the soil. The water‐soluble toxicant 1080 was rapidly leached from bait into soil. Leaching began after only 20 mm of rainfall. Soil concentrations under baits reached a maximum concentration in soil after 100 mm rainfall and declined to near the limit of detection after 250 mm. Pindone concentration in baits declined by 23% after 400 mm of rainfall, but no pindone was found in the soil. Cholecalciferol and brodifacoum concentrations in bait did not decline at all, but trace amounts of cholecalciferol were found in soil under baits. These results demonstrate that if baits containing hydrophobic toxicants, such as brodifacoum, are hand‐laid or spilt from bait stations, they will remain hazardous to livestock and non‐target species, even after exposure to substantial amounts of rainfall.

Cyanide is a fast-acting toxin that has great potential for use as a disease sampling and research tool for invasive species such as feral pigs and foxes. Both species can be successfully targeted using poison baits, but current registered toxins are not suitable for disease sampling due to considerable delays between consumption and death. Incorporation of cyanide into a stand-alone bait for both pigs and foxes would be the preferred product for dropping animals quickly for disease surveillance. The research detailed in this report focused on such products. We completed pen trials on feral pigs using a variety of bait packages, ejectors and cyanide formulations (powder, paste and liquid). Despite considerable successes, the results from these trials indicated that, with current encapsulation technology and at ‘pig-size’ doses, it appears difficult to disguise the distinctive smell and taste of cyanide. This in turn results in difficulties delivering effective lethal doses (since th...