Farmers battling the worst rat plague ever seen across Western Australia say solutions are bogged down in red tape.
An estimated 8,000 rats live on every hectare in northern Washington’s grain belt, and swarms can be seen on pastures and on roads at night.
Grain producers say current doses of the toxic zinc phosphide are ineffective and that twice the dose (50 grams per kilogram) is needed.
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However, the Australian Pesticides and Veterinary Medicines Agency (APVMA) has refused permission to manufacture it.
Rat welfare issues
John Waugh farms 20,000 hectares of land near Una, 500km north-east of Perth, and runs aerial spraying operations in WA and New South Wales.
He said a rat would die if it ate one bait made with higher concentrations of the poison, but would need to eat at least two baits to die at the standard 25g/kg.
“Any animal that is a pest wants to be put out of its misery as quickly as possible, and rats are no exception,” he says.
John Waugh said he had never seen so many rats on his farm near Yuna, Western Australia. (ABC Midwest Wheatbelt: Chris Lewis)
“This is definitely a welfare issue for the rats, but it’s also a social issue.” [too].
“In rural towns, you can just walk into the local store and immediately smell rats. As farmers, we have dead rats all over our houses and sheds.”
Poison bait refused
Manufacturer and producer group Grain Producers of Australia (GPA) unsuccessfully applied to the APVMA for emergency permission to produce double-strength feed.
Their application cited CSIRO research on the improved effectiveness of high concentrations of zinc phosphide, but APVMA said the data was “not of sufficient regulatory quality”.
“It’s really mind-blowing that here we are in 2026. We’ve had rat epidemics across Australia for the last 10 years or so and we’re still quantifying that that data is incorrect,” Mr Waugh said.
Significant numbers of rats have been reported throughout Washington state’s agricultural areas. These holes are located in a paddock near Raventhorpe on WA’s south-east coast. (Provided by: Henry Marsh)
He said time was of the essence and his conservative modeling showed the rat blight could cost WA farmers $50 million in crop damage in the coming weeks.
Observe research
CSIRO has published four papers examining the effectiveness of zinc phosphide, all of which show that a rate of 50g/kg of zinc phosphide is more effective than 25g/kg in mouse controls.
CSIRO researcher Steve Henry, a co-author of the paper, said he supported the research.
“Virtually all four studies showed exactly what farmers were telling us, which is that 25g/kg feed is consistently ineffective,” he said.
Rat activity is widespread across Australia. (Provided by: CSIRO)
He said so far there was no indication that higher concentrations of zinc phosphide increased the risk of secondary poisoning in birds, but scientists were continuing to study this area.
The APVMA has been contacted for comment.
Andrew Weidman seeks farmers’ experience using rat baits of varying strengths. (ABC Wimmera: Gillian Aelia)
GPA research and development spokesperson Andrew Wideman said the producer group is now scrambling to obtain more information to meet APVMA’s requirements and obtain emergency permit approval.
He said the GPA had approved an emergency permit to manufacture high-strength baits in 2021, which was supported by CSIRO research, but a subsequent application was rejected.
“We hope that the weight of the evidence will be enough data to at least ensure that we can secure an emergency permit and be able to expand. In the future, this will be fully registered and available to producers.”
Bare fields of rapeseed fields show how much damage rats can cause to vast crops. (Provided by: Monica Field)
GPA is inviting farmers across the country to share their experiences with the effectiveness of rat baits through its website.
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