Farmers battling the worst mouse plague they have ever seen on farms across Western Australia say a solution is being stalled by red tape.
An estimated 8,000 mice live in every hectare of WA’s northern grain belt, and swarms of them are visible in paddocks and on roads at night.
Grain growers say current dosages of the poison zinc phosphide are not working, and a double dose, measuring 50 grams per kilogram, is needed.
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But the Australian Pesticides and Veterinary Medicines Authority (APVMA) is refusing to allow its manufacture.
Mice welfare issue
John Warr farms 20,000 hectares of land near Yuna, 500 kilometres north-east of Perth, and owns aerial application businesses in WA and New South Wales.
He said a mouse would die after eating one bait made with a higher rate of poison, but needed to eat at least two baits to die with the standard 25 grams per kilogram.
“Any animal that’s a pest, you want to put it out of its misery as soon as possible, mice are no different,” he said.
John Warr says he has never seen so many mice in his paddocks near Yuna in Western Australia. (ABC Mid West Wheatbelt: Chris Lewis)
“This is definitely a welfare issue for mice, but it’s a social issue [too].
“In country towns, soon as you go into the local shop, all you can smell is mice — as farmers we have dead mice all through our houses and sheds.”
Poison bait rejected
Manufacturers and grower group Grain Producers Australia has unsuccessfully applied to the APVMA for emergency permits to manufacture the double strength baits.
Its application cited CSIRO research on the improved efficacy of higher rates of zinc phosphide, but APVMA said the data “is not of sufficient regulatory quality”.
“I just find it absolutely dumbfounding that here we are in 2026, we’ve had mouse plagues around Australia for the last decade or so, and they’re still quantifying that the data isn’t correct,” Mr Warr said.
Significant number of mice are being reported across WA’s farming region. These holes are in a paddock near Ravensthorpe, on WA’s south east coast. (SUPPLIED: Henry Marsh)
He said time was of the essence, and his conservative modelling showed a mouse plague could cost farmers in Western Australia $50 million in damage to crops over the next few weeks.
Standing by the research
The CSIRO has published four papers examining zinc phosphide efficacy, which all found 50 gram rate of zinc phosphide is more effective than 25 grams in controlling mice.Â
CSIRO research officer Steve Henry co-authored the papers and said he stood by the research.
“Effectively all of those four studies have shown exactly what farmers were telling us, that the 25 gram bait doesn’t work consistently,” he said.
Mouse activity is widespread across Australia. (Supplied: CSIRO)
He said so far there was no indication a stronger rate of zinc phosphide increased the risk of secondary poisoning to birds, but scientists were continuing to study this area.
The APVMA has been contacted for comment.
Andrew Weidemann is asking for farmers’ experiences of using various strength mouse baits. (ABC Wimmera: Gillian Aeria)
Grain Producers Australia’s research and development spokesperson Andrew Weidemann said the grower group was now scrambling to get more information to try and satisfy the APVMA and get emergency permits approved.
He said GPA had emergency permits approved in 2021 to manufacture the high strength bait, which was supported by the CSIRO research, but subsequent applications had been rejected.
“We hope that the weight of evidence will be enough data to ensure that we can at least get the emergency permit up and growing, and in the future we see this fully registered and available for growers,” he said.
Bare ground in a canola paddock shows just how damaging mice can be to broadacre crops. (SUPPLIED: Monica Field)
GPA is asking farmers nationally to share their experiences on mouse bait efficacy via its website.