PADDOCK hygiene and constant vigilance will be critical in the battle to keep mouse numbers down in the autumn following ideal conditions for breeding over the summer.
Mouse researcher Steve Henry, CSIRO, said numbers were already building up to worrying levels in parts of the country including NSW's Central West that bore the brunt of the devastating mouse plague in 2021.
"We have been doing some trapping in the Trangie area and the numbers are building, suggesting that after the floods of last year, which kept things in check, there has been a fairly quick build in populations," he said.
"Elsewhere, in locations like the Adelaide Plains, the results showed we did not catch that many mice but there are plenty of signs of them, the issue may be that there is just so much food around we are not catching them."
"It has been a mild summer and there is plenty of feed around for mice so people will need to be alert to the risks."
Speaking at the Grains Research and Development Corporation update in Adelaide last week Mr Henry said farmers could help reduce their risk by keeping the amount of grain and stubble in paddocks to a minimum.
He said this would pave the way for an effective baiting program in the autumn.
"The best baiting results are achieved when there is as little alternative food in the paddock as possible."
"When baiting at sowing the idea is that the mice will take the bait on top of the ground rather than dig for the grain seed."
Mr Henry said the switch to double strength zinc phosphide baits was changing the way farmers approached their baiting programs.
"Previously it was recommended they go out a few weeks prior to sowing and run numbers down before another baiting program at sowing."
"With the kill rates we are achieving with the double strength zinc phosphide that does not seem necessary, we feel there will be good control with just the single baiting, providing numbers are not too high.
"It is all about being strategic, rather than frequent with baiting, and the time of sowing, when feed is at its lowest availability, is ideal."
Mr Henry explained the push towards 50 gram zinc phosphide per kilo of wheat baits rather than the 25g/kg baits previously registered for use.
He said research had found mice were less sensitive to zinc phosphide than previously thought.
"It takes two milligrams of zinc phosphide to kill a 15 gram mouse, not the 1mg that the original zinc phosphide bait was based on."
Researchers looked into this after growers alerted them to concerns 25g/kg bait was not working effectively.
"I remember meeting with growers in the Victorian Mallee and we still thought the 25g/kg bait was doing the job, one farmer just about shook me by the shirt passionately telling me that it was not working."
"It turns out a lot of our trial work was done in areas with low levels of background food, where efficacy would be higher, and in those areas with standing stubbles and grain on the ground it would be a lot lower."
Mr Henry said it was critical to get good kill rates the first time around as research had discovered that mouse aversion to bait is rapid after a non-lethal dose and the duration of that aversion is unknown.
He said this year with up to 0.5 tonnes a hectare of grain left behind due to harvesting difficulties in wet crops farmers needed to try and run the food bank down to ensure mice were being controlled.
"Mice eat three grams of food a day, which means they need about 66 grains a day to survive."
"We get frequent reports of significant grain loss, and if you've got 0.5t/ha left behind, that's 1000 grains a square metre, compared to around three grains/sqm of bait.
"You've really got to make sure every grain of bait is a lethal dose because the chances of a mouse discovering a second toxic grain amongst all that other background food are really low."
He said farmers could look to run down the available feed with livestock and should also spray out volunteer crops that have germinated on summer rain.
