Morton Plains, south of Birchip, farmer Neil Davis said he could not begin to estimate numbers per square metre, but said they were well above the threshold recommended for baiting.

“We’ve just got these burrows, every 10cm apart in some paddocks, and where we’ve baited, you can find four to six dead mice in each hole.

“That gives you an indication just how thick they are.”

Mr Davis said one of his worst impacted paddocks was an unharvested field pea crop.

“The crop would have yielded up to 2t/ha, so there is plenty of food and plenty of shelter.”

However, he said he was pleased with the impact of the bait, MouseOff.

“It seems to have done a very thorough job.”

He said his major fears for mice damage were for canola and pulse crops.

“The numbers are certainly there to do some damage if they aren’t controlled.”

Mr Davis said he was hopeful the baiting would be effective enough that it only required one application.

Meanwhile, in NSW, growers have another control option, with an emergency permit for Bromadiolone, available through the state’s Livestock Health and Pest Authority.

More than 100 tonnes of grain has been treated with the chemical, which has been approved for use as a crop perimeter bait.

Usually, the product is only registered for use around grain storages and farm buildings.

However, authorities warned that the registered zinc phosphide product would be more effective if mouse numbers were rapidly rising.

The problem remains getting hold of bait, although shortages have eased somewhat in recent weeks.

Birchip Cropping Group (BCG) has reported mice activity has also slowed down slightly with the advent of cooler conditions, however, they said repeat baiting has been necessary in some paddocks.

Linton Staples, managing director of Animal Control Technologies Australia (ACTA), the company that manufactures MouseOff, said it was the largest mouse problem nationally in the company’s 15 years of operation.

The company has been producing MouseOff at full capacity to ensure as much demand is met as possible.

He said the reason supplies became tight was because the mouse problem flared up one to two months earlier than is common.

The team at PestFacts have said one of the key reasons for the mouse plague has been the availability of food, with large amounts of spilt grain, knocked from the plant during the harvest rain, available for the rodents.