VICTORIAN grain growers are facing an unusual "double whammy" of potentially devastating plagues of locusts and mice.

Locusts have been creating havoc in the north and northwest of the state but mouse numbers have also been steadily building up in the Mallee, Wimmera and Western District.

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Victorian Department of Primary Industries mouse advisory committee convener Banjo Patterson said the seasonal spike in mouse numbers was higher than normal, especially in the Southern Mallee and Wimmera.

"We normally expect a seasonal spike, but this one is bigger," Mr Patterson said.

Rupanyup grain grower Andrew Weidemann said mice were already invading farm buildings and contaminating cereal hay.

The most worrying aspect of the infestation is the ability of mice to eat newly sown cereal and canola crops.

"We've been baiting after sowing because they're quite active and looking for the grain," Mr Weidemann said.

Animal Control Technologies sales and marketing manager Phil Morrow said farmers in the state's west needed to continue to monitor mouse numbers and bait when they reached problem levels.

"The situation in western Victoria is quite bad but more stable than other parts of Australia," Mr Morrow said.

"In Western Australia and on the Yorke Peninsula in South Australia the mouse problem is very bad.

"While locust and mouse plagues (occurring concurrently) are not rare, it is a difficult set of management conditions farmers are facing."

Crop sowing provided feed for mice.

Mr Morrow said if mouse numbers built to 1000/ha, they could devour about 5 per cent of planted seed each night.

"It doesn't take very long for very serious losses of crop to occur at the beginning of the season," he said.

Baiting costs about $10-$12/ha to control mice.

Grains Research and Development Corporation crop protection manager Rohan Rainbow said the there were many strategies to minimise mouse damage on a farm.

Some of these techniques included:

Achieving accurate, deep sowing depths (within crop emergence/productivity limits) and carefully considering the risks of mice predation if sowing dry.

Checking all unbaited, newly sown crops regularly, especially one or two days after sowing, for signs of mouse damage.

Thinking on a whole-farm basis because mice were very mobile.

Paying special attention to areas where harvesting efficiency was poor last year.

Being alert to damage at tillering and head emergence, particularly in areas affected by summer storms or in self-sown crops.