The New South Wales government has applied for “urgent approval” to use a poison called bromadiolone on farms, as part of a $50 million package to help regional areas deal with the mouse plague.
- The NSW government is seeking permission to use a chemical equivalent to “napalm” to control the mouse plague
- Scientists and ecologists are worried widespread use of the chemical could also kill pets, livestock and native wildlife
- The NSW Farmers Association says the response is too late to save winter crops in some areas already destroyed by mice
Bromadiolone can be bought over the counter in Australia for use at home, but is not allowed on farms because of the risk it poses to other animals.
NSW Agriculture Minister Adam Marshall said the state government had sought approval from the Australian Pesticides and Veterinary Medicines Authority (APVMA) for farmers to use bromadiolone to control mice on their properties.
“It’ll be the equivalent of napalming mice across rural NSW,” he said last week.
In the United States, the Environmental Protection Agency has said poisons like bromadiolone can only be used by registered pest controllers because of the risk to “off-target” animals.
How does the poison kill mice?
Bromadiolone blocks the production of vitamin K.
The vitamin is essential for blood clotting and the poison eventually leads to the rodents bleeding out, according to Michael Lohr from Edith Cowan University.
The zoologist and adjunct professor said the delayed onset of the poison was part of the reason it was such an effective killer.
“On first contact with the rodenticide they don’t feel sick and it allows them to come back and continue to consume more, which is why it’s such an effective rodenticide.”
Mr Lohr said bromadiolone had been given emergency approval in previous mouse plagues in New South Wales but was outlawed in most countries around the world for use in agriculture.
Mr Lohr said the problem with bromadiolone, compared to other poisons, was that it didn’t break down after the mouse was killed and could cause problems with anything that consumed the dead rodents or the bait itself.
Concern for other animals
Ecology academic Dr Maggie Watson, of Charles Sturt University, has warned the $50 million package to control the mouse plague could kill a lot more than just mice.
Dr Watson said bromadiolone was a highly lethal second-generation poison that could easily cause secondary poisoning in animals, including farm animals such as cattle and working dogs.
“Unlike zinc phosphide, the poison builds up in the body in the fat and in the liver and that is much less of a problem with the zinc phosphide bait as the poison quickly disperses as a gas.”
She said double strength zinc phosphide was the best option as it was much less likely to kill unintended wildlife, including birds of prey.
Dr Watson said she hoped chemical regular APVMA would think carefully about the approval, given widespread concern about off-target damage caused by bromadiolone.
She said a number of her colleagues at the university’s veterinary school were behind the scenes campaigning to prevent the approval of bromodiolone.
Some farmers sceptical
NSW Farmers Association vice president Xavier Martin said his members were frustrated with the government’s belated response to the “natural disaster”.
“There’s just so many aspects of this proposal around bromadiolone that just don’t add up,” he said.
Mr Martin said that even with approval the bait would likely be hard to source from overseas markets in time to benefit farmers.
He said the measures were too late to help winter crops, with reports farmers had already lost freshly sown paddocks to mice.
“We need it now, and that’s why I’m hearing from members they are enormously annoyed,” Mr Martin said.
The $50 million package was announced just two days after the Country Women’s Association and NSW Farmers teamed up to call for more help with the plague.
‘There is going to be a cost’
When announcing the package, Agriculture Minister Adam Marshall said farmers would be able to get grain treated with poison “absolutely free of charge” to help combat the rodents.
The minister said he was “confident” the APVMA would approve the application to use bromadiolone on farms, “which is currently illegal because it’s so strong”.
The APVMA said it had received an emergency application to use “a registered product in a manner not currently authorised by the label directions”, and that it was assessing the request.
Mr Marshall conceded that the use of bromadiolone would likely result in the deaths of other animals.
“There is going to be a cost to this for some other animals but it’s something that’s been factored in and we just have to take this step.”