Australian grain farmers are heading into seeding season with the looming threat of a mouse plague.
Researchers have recorded between 100 and 200 mice per hectare at some monitoring sites on South Australia’s Adelaide Plains, with the numbers touching 400 to 600 a hectare where traps are reaching saturation point. A plague is officially defined as 800 mice per hectare.
The stakes at seeding time are especially high. Mice dig along seed furrows as crops go in, consuming grain before it can germinate. Farmers describe the visible damage as UFO rings, or circular patches of bare earth around mouse burrows where grain is systematically consumed, thinning crops across large areas.
Growers near Geraldton and Ravensthorpe in Western Australia have been sharing footage of mice moving through paddocks and stubbles while residents in Morawa, about 360km northeast of Perth, have described coming home to mice overrunning their pantries.
Andrew Weidemann, research and development spokesperson for Grain Producers Australia, said the mouse threat was the latest in a series of blows for growers, who had already cut paddock movements to conserve fuel.
“This warning comes as grain producers are already dealing with increasing uncertainty about fuel and fertiliser access due to escalating global conflict affecting trade routes,” he told ABC Rural.
Pest controller Peter Cekanauskas told the ABC he put out 7.5kg of bait and it was consumed in less than three days. “It was like a horror story,” he said.
The last major mouse plague, in 2021, caused an estimated damage of $1bn across several states, with rural New South Wales alone suffering losses of around $660m. Scientists and agronomists say the industry is better prepared this time, with improved understanding of how zinc phosphide bait works and earlier warning systems in place.
“After the seed is gone, the plant is gone. There’s no replacing it,” Steve Henry, research officer at the Commonwealth Scientific and Industrial Research Organisation, told ABC Rural, warning high-value crops such as canola were at particular risk given seed shortages this year.
Elevated numbers have been seen across a broad stretch of the country, with CSIRO flagging concerning populations from Geraldton to Esperance in Western Australia and into southern Queensland. Western Australia’s Kwinana West region has been assessed as high risk. Mouse populations can escalate rapidly, with small numbers turning into large infestations within weeks.
The threat comes at a moment when farmers are already under compounding pressures, contending with fuel shortages and spiralling fertiliser prices from disruption to global trade due to the US-Israeli war on Iran.
Roughly 20 to 30 per cent of global fertiliser supply comes from the Middle East, and the effective closure of the Strait of Hormuz has halted the exports of urea, ammonia and phosphate from Saudi Arabia, the UAE and Qatar.
Australia imported 3.85 million tonnes of urea in 2024, almost entirely from the Middle East. It has virtually no domestic production capacity after its only urea manufacturing facility closed in 2022.
The world price of urea increased from A$675 (£357) per tonne in February to more than A$1,000 (£530) at the end of March. Industry estimates say Western Australia’s grain harvest could fall from a record 27 million tonnes last season to around 15 million tonnes – a drop of nearly 45 per cent – if fertiliser supplies remain insufficient.
“Even if fertiliser can be sourced from elsewhere in the world, it may not arrive in time,” Professor Marit Kragt from the Centre for Agricultural Economics and Development at the University of Western Australia said.
“Fertiliser and fuel costs constitute 25 to 30 per cent of a cropping business’s total farm costs, so a sharp increase in both will significantly affect farm profitability.”
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