CSIRO scientist Steve Henry and a student process a captured mouse.
New research has found mice numbers can be reduced on farms by doubling the amount of zinc phosphide used in grain baits.
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The research by Australia’s national science agency CSIRO was partly carried out on farms at Parkes in central western NSW and has been published in the internationally peer-reviewed journal Wildlife Research.
The Grains Research and Development Corporation funded the project and followed concerns from farmers that mouse baits were not effective, especially when numbers hit plague proportions.
“We listened to farmers. They told us there was a problem ... and now we’ve come up with a solution that we think will deliver some really favourable results,” CSIRO scientist Steve Henry said.
CSIRO researchers carried out a series of studies to reassess the sensitivity of mice to the poison.
The paper was published on August 3 and is the third in a series.
Higher than usual mice numbers have been reported in northern Victoria.
Mr Henry said when scientists increased the dose of zinc phosphide in the bait it killed 90 per cent of the mice, 80 per cent of the time.
That compares with 80 per cent of the mice dying only 20 per cent of the time, using the current 25 grams of the poison per kilogram.
“It’s buying some certainty for farmers about the effect of their baiting effort,” Mr Henry said.
He said the chances of secondary poisoning of other animals were extremely low because the zinc phosphide was used up in the process of killing the mice.
He said poisoning of birds in particular was unlikely because the chance of them finding the toxic grains was very low.
“We never see dead birds near paddocks that are associated with baiting.”
GRDC pests manager Leigh Nelson said the three studies showed when the grain bait had 50g of zinc phosphide per kilogram it wahs far more effective.
“The (higher dose) should reduce the need for repeat baiting which is costly,” Dr Nelson said.
"Any savings on the bottom line from mouse damage would be welcomed by farmers.”
CSIRO has also reported higher than normal mice populations in southern Queensland and northern Victoria.
Zinc phosphide was introduced in the early 1990s and today farmers are only allowed to spread baits of one kilogram of the wheat bait per hectare.
During the 2021 mouse plague, an emergency permit was granted to increase the concentration from 25g to 50g of zinc phosphide per kilogram of grain bait.
The Australian Pesticides and Veterinary Medicines Authority, which approves the amount of zinc phosphide used, said “all applications are assessed against the statutory criteria to ensure the proposed use will be safe and effective’’.
A spokesperson from the authority said the environmental effects of using double dose zinc phosphide were carefully considered prior to issuing the permits.
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