CSIRO research points to concerning mouse numbers in paddocks stretching from Geraldton to Esperance in Western Australia.
Monitoring zones have also recorded increased numbers across South Australia's Adelaide Plains, Yorke Peninsula and Eyre Peninsula, along with parts of southern Queensland.
Wimmera farmer and Grain Producers Australia research and development spokesperson Andrew Weidemann has urged farmers to be prepared to bait for mice at sowing time in autumn.
He said rising pest numbers are the latest challenge for farmers, who have reduced paddock movements to conserve fuel, while supply shortages continue to affect the sector.
"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," Mr Weidemann said in a statement.
Authorities warn mouse populations can increase rapidly, with small numbers turning into large infestations within weeks.
"Growers around Geraldton and Ravensthorpe have been sharing photos and short videos showing mice moving through paddocks and stubbles ahead of the coming season," Mr Weidemann continued.
"These are firsthand observations from growers on the ground and, while it is too early to draw conclusions about how widespread the issue may become, the level of activity being reported has clearly raised concern."
CSIRO rapid assessment monitoring also suggests there is high risk for Western Australia's Kwinana West region.
There are relatively low numbers across Victoria and southern and central west parts of NSW.
Farmers were being urged to harvest as cleanly as possible to limit the rodents' food supply, then watch out for increased mice numbers in crop stubble.
After a mouse plague in 2021, which caused an estimated $1 billion worth of damage across several states, the agriculture industry was better prepared for another disaster, CSIRO research officer Steve Henry told AAP in November.Â
Subsequent lab tests and field trials had helped scientists better understand how the toxin zinc phosphide worked to eradicate mice.
A single rodent needed to eat two or three poison-coated grains to receive a lethal dose.
Research after the 2021 disaster calculated the cost of damage to rural NSW alone was $660 million, a figure that informs action to prepare for another plague.
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