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Managing Risk When Controlling Vermin

The term "vermin" is a broad term that generally relates to a range of vertebrate pests such as rats and mice, foxes, wild dogs, rabbits and hares.

By Department of Primary Industries - 11th August 2004 - Back to News

Control of any pest is best achieved with an Integrated Pest Management (IPM) plan that utilises a range of strategies to achieve the best possible level of control. In IPM the strategies available include:

• Physical control - such as using a bulldozer with rippers to destroy harbour, warrens, or dens;
• Cultural control - such as changing lambing paddocks to a paddock where there is less cover for foxes;
• Biological control - such as Rabbit Calicivirus Disease used in the control of rabbits;
• Genetic control - such as resistant varieties (not yet used in vermin control in Victoria);
• Quarantine - such as fencing out a forest block to "quarantine" the paddock from the pests; and
• Chemical control - such as poison baits used to control a range of vertebrate pests.

Assuming that an Integrated Pest Management program is implemented using a range of the strategies listed above, it is reasonable that chemical control may play a part in the program.

Chemicals used for vermin control are formulated in a number of ways. For example, aluminium phosphide tablets used in rabbit control react with moisture in the air to release toxic phosphine gas that fumigates the treated warren. Other chemicals produce carbon monoxide gas or chloropicrin gas to fumigate the burrow or den.

These chemicals require a high level of expertise and diligence in their use, as fumigant gases can have significant and acute adverse effects on the user when things go wrong. In addition, most of these fumigant chemicals are Schedule 7 Dangerous Poisons, and the user must have completed a course in safe chemical use and must hold a proper authorisation for their use.

With vermin, bait formulations are often used as a part of the pest management plan because it is not always easy or possible to identify a den, nest or warren. The pest may also be transient in an area as in the case of foxes, and in the case of mice infestations there may simply be too many holes in a paddock to treat each one individually.

Baits are potentially a concern because by their nature they contain a food source to attract the pest, and a poison to kill the pest. We don’t want to be attracting non-target animals such as native marsupials, or the neighbour’s dog to the bait. To overcome this potential concern, registered baits are formulated to deter or limit their attractiveness to non-target animals.

This is achieved through a range of strategies such as:

• formulating the bait using a chemical that is more selective to the pest than to non target animals;
• the addition of bittering agents to limit bait intake by non target animals;
• colouring the bait to make it unattractive to non target animals;
• using only a certain amount of bait;
• leaving the husk on grain bait, or removing it depending on the nature of the target animal;
• burying the bait to make it unavailable to non target animals; or
• covering the bait after a certain period of time to limit access by non target animals.

For some bait formulations, there is also a requirement to post warning signs and to notify neighbours so they can take precautions to prevent any unwanted access to the baits. Each of these strategies works to ensure that the pest animal is targeted, and that the risks to non-target animals are minimised.

Unfortunately, people sometimes illegally use other chemicals they may have access to, and make baits to control animals they view as vermin.

In these cases the bait will most likely not be formulated to limit access by non-target animals, and DPI does receive complaints in relation to this issue from time to time.

Experience shows that when illegal baits are used, their effects are generally non-selective to the targeted pest, and the negative outcomes can be frightening.

For example, a person laid a home made grain bait to control corellas (which is illegal in any case because these birds are protected), and killed not only corellas, but cockatoos, ducks, magpies, mudlarks, brown hawks, kookaburras and a range of other bird species. Not all of these birds eat grain, and it is likely that the raptors like the hawks and kookaburras were poisoned after they fed on other birds (or animals) that had died from eating the grain bait.

In another example of illegal baiting, a person living on the outskirts of a sizeable rural city prepared and laid baits made from meat laced with strychnine to poison foxes, but instead killed a number of the neighbours’ domestic dogs. The grief this caused the local residents was both considerable and unwarranted.

Bait formulations must be used strictly according to the label Directions for Use to ensure the best possible outcome, and like the fumigant formulations described above, many of them are restricted supply or restricted use chemicals, or both.

In addition, the penalties for misuse of vermin baits are significant, and if non-vermin animals are targeted, the penalties are even more significant, and can include the imposition of heavy fines and in some cases, even terms of imprisonment.

Chemicals can play a vital role in an integrated vermin control program, in helping to ensure the best possible outcome is achieved, but these chemicals need to be used carefully, and in accordance with the label Directions for Use.

For further information on vermin control or vermin control chemicals contact your local DPI Catchment Management Officer, or your DPI Regional Chemical Standards Officer.

Source: http://gippsland.com/

Published by: news@gippsland.com

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