Over 500 people tuned into a GRDC-run mouse management online seminar last week, highlighting the mounting concern, especially down the east coast, at rising mouse populations.

However, while there are still unknowns, researchers said the core principles of reducing feed stock and targeted baiting remained the cornerstones of an effective mouse minimisation strategy.

Main speaker at the event, CSIRO mouse management specialist Steve Henry said predicting mouse behaviour was not straight forward.

"There are plenty of times I have an idea and I'm proved to be wrong, it is the difficulty in working with animals that have a brain and can behave unpredictably," Mr Henry said.

He reaffirmed the first thing growers needed to do was get out in the paddock and assess numbers.

However, he cautioned growers that it was not as simple as doing a quick check out for burrows.

"On vertisol soils with big cracks you might not always get visible burrows, if that is the case you may need to use chew cards to get an accurate number," he said.

Mr Henry said farmers also had to be accurate when making burrow counts.

"An extra burrow you count as in your square metre is an extra thousand a hectare, it adds up."

On the baiting front, Mr Henry said while it could be tempting to combine mouse bait with product to control other pests such as slug and snail bait or even urea fertiliser it was a definite no-no.

"If you were to put it into urea, as it is agitated with the urea in the spreader the zinc phosphide is being scraped off the surface of the grain.

"Because you are scraping zinc phosphide off the grain you are increasing the chance of the mice getting a sublethal dose, causing aversion."

"The second problem is you are putting it out with urea, so there are two new things going into the paddock. If the urea tastes bad for mice they will not eat the new bait either but will go back to what they were eating before."

Mr Henry said for farmers in winter cropping systems the best way forward was to get rid of much foodstuff as possible.

"Sheep are a great tool for this and if you've been lucky enough to get summer rain some of the seed from last year's crop should have germinated and you can spray it out."

However, he said the issue is more difficult in summer cropping where the mice will have the option of feed in the sorghum head.

"The best thing to do, although not perfect, is to continue baiting as generally the mice will prefer to feed along the ground where there is less danger."

In sobering news for growers who had grain blow onto the ground prior to harvest, Mr Henry outlined that the average mouse needed 3 grams, or around 22 grains of a cereal crop, per day to survive.

He said a tonne to the hectare of spilt grain, which many growers experienced, equated to 2200 grains a square metre, meaning plenty of food for mice to survive on over summer.

"This is why we need to try and control the amount of feed first, make the stubble inhospitable for mice."

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