Australian grain growers are urged to create hostile environments for mice by reducing residual food supplies and thereby optimising the effectiveness of baiting programs.

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 GRDC specially convened online mouse forum. The Update was recorded and is available for viewing and downloading via GRDC's website.

GRDC-supported lead mouse researcher Steve Henry from CSIRO, Australia’s national science agency, 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. 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,” Mr Henry told the 330 forum participants.

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 GRDC responded swiftly by organising an online Grains Research Update through Independent Consultants Australia Network (ICAN).

Mr Henry reported on the extent of the current situation across the nation, which included:

• Central Queensland and Darling Downs – mice are in high numbers, with reports of unusual activity outside the cropping zone in western Queensland
• Northern NSW – summer crops and cotton crops are being hit hard
• Riverina – high numbers are again leading to serious concerns. Summer crops are supporting high numbers
• Victorian Wimmera – many reports of high numbers for this time of the year, but populations are patchy
• South Australian Mallee – high numbers in some areas
• WA – higher than usual numbers in the Ravensthorpe region.

Mr Henry says mice in some regions 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.”

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 says 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 says 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:

• Put mouse bait out before other pest/nutrient treatments. This gives mice the chance to encounter zinc phosphide bait before they discover any other new substances in a paddock and reduces the likelihood of a sub-lethal dose and therefore bait aversion
• Do not mix mouse bait with snail/slug bait and do not apply mouse bait with a surface application of urea. Zinc phosphide can be scraped off the surface of the treated grain when agitated with other substances
• Burning stubbles is unlikely to impact on mouse populations but it may improve results with baiting (due to less food competition)
• Bait on the ground is more likely to be taken before mice climb plants to eat developing seed heads of sorghum crops
• Do not bait ahead of a significant forecast rain event
• Co-ordinate baiting strategies with your neighbours for area-wide management and highest impact.

In the meantime, more details about control options are available via the GRDC's Mouse Control website.

Mr Henry also urges growers to report and map mouse activity – presence and absence – using MouseAlert and Twitter @MouseAlert so other growers can see what activity is being observed in their neighbourhood.

GRDC has invested in a major mouse-related research, development and extension program that is continuing to reveal new insights about mice in Australian broadacre cropping systems. The work is investigating mouse biology, ecology and bait efficacy.

Results from current research efforts will form the basis of a series of recommendations for improved mouse control strategies for Australian grain growers.