Mice numbers increasing as GRDC urges growers to reduce food

Limiting competition for bait by eliminating alternative food sources is the pivotal mouse management strategy available to growers who are dealing with a worsening mouse situation in some of Australia's key cropping regions.

Creating 'mouse unfriendly' paddocks was a key piece of advice delivered to growers and advisers during the recent Grains Research and Development Corporation's specially convened online mouse forum.

GRDC-supported lead mouse researcher Steve Henry from the CSIRO stressed the importance of increasing the odds of mice encountering a lethal dose of zinc phosphide bait.

"If mice are hungry, they are more likely to eat a lethal dose," he said.

"You get a much better result if the rate of bait encounter is increased by having less residual food in paddocks, and the likelihood of bait aversion through ingestion of a sub-lethal dose is reduced."

Mice have been ravaging freshly planted summer crops in parts of northern New South Wales and Queensland and are in large numbers elsewhere across eastern and southern states.

With concern mounting about further impact to summer crops ahead of grain fill and harvest and the potential threat to the 2021 winter grain crop, the forum was convened to brief the nation's grain growers and their advisers.

The need for such a forum was identified by farmer representative organisation AgForce, and the GRDC responded swiftly by organising an online Grains Research Update through Independent Consultants Australia Network.

Mr Henry reported on the extent of the current situation across the nation, which included many reports of high numbers in the Wimmera, although populations were patchy.

He said mice in some regions in eastern Australia were in breeding condition which was a cause for concern heading into autumn, the traditional winter crop sowing period.

"If conditions are favourable - mice need food, shelter and moisture to thrive - the rate of population increase is dramatic," he said.

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Mice start breeding when they are six weeks old, and litters of six to 10 pups are born every 19 to 21 days.

Mr Henry encouraged growers to control volunteer cereals, remove grain on the ground around storage infrastructure, and where possible use sheep to clean up residual grain from the 2020 harvest.

Limiting grain losses during harvesting of summer and winter crops is also imperative.

"One tonne per hectare of grain lost at harvest equates to 2200 grains/square metre. Zinc phosphide bait is spread at one kilogram/ha or three grains/square metre - underlining the importance of reducing alternative food sources to enhance baiting success."

Mr Henry said baiting six weeks out from sowing was advisable if mouse numbers were currently high.

This allowed mice to overcome any sub-lethal ingestion and bait aversion before baiting at sowing time.

"If you still have mice at sowing, put the bait out off the back of the seeder. You will get the primary bang for your buck baiting at sowing, especially if the bait goes on freshly disturbed soil after the last presswheel."

Mr Henry said close monitoring after each bait application was critical, and it was important that growers actively and thoroughly monitored their paddocks for mice.

"Go for a walk through your stubbles and look for signs of activity. And be prepared to bait - talk to your bait suppliers early."

Mr Henry also offered the following advice:

Mr Henry also urges growers to report and map mouse activity - presence and absence - using MouseAlert (www.mousealert.org.au) and via Twitter using @MouseAlert so other growers can see what activity is being observed in their neighbourhood.