Active holes can be identified by sprinkling talcum powder around holes and inspecting the level of disturbance the following morning. One burrow per 100 square metres equals 100 burrows ☺per hectare, or 200 mice per hectare. Burrows usually contain 1 to 4 mice but can have up to 40 mice.

Checks should be made across a paddock as populations can be patchy. Hole counts vary by soil type. In cracking soils, holes may be difficult to identify. In sandy soils, mice may dig many holes in search of seed, which can look similar to nesting burrows. In hard-setting soils, there may be few holes but each can contain many mice – up to 40 per hole during plagues.

Mouse chew cards or ‘Canola’ squares: this method is most reliable in late autumn/winter when food is scarce. It is less reliable as crops mature, because the crop provides a more attractive food source than canola-soaked card.

• Each sampling area requires 10 pieces of strong paper or light card (10cm by 10cm), marked with a 1cm grid and soaked in canola or linseed oil.
• Place the cards randomly across a paddock and peg them to the ground.
• If more than 10 squares per card are eaten overnight, significant mouse populations are emerging.
• If more than 20 squares per card are consumed in immature crops, there is a significant mouse problem.

Economic damage is likely when there are 200 to 300 mice per hectare at sowing (1 to 2 active burrows per 100 m transect) and baiting is critical. Two hundred mice per hectare can eat 1 per cent of the crop sown each night, or 14 per cent in two weeks.

Aerial or ground application can be used to spread zinc phosphide bait. A rate of 1kg/ha provides 20,000 lethal doses per hectare. It can be spread in stubble, pasture and crop, or a vegetative fallow, but not on bare ground. Baiting is less effective when alternative feed sources are available, so growers should endeavor where possible to clean up grain spills, control weeds and reduce food sources (eg graze sheep on stubbles).

Aerial or ground application can be used to spread zinc phosphide bait at a rate of 1kg/ha.

A wide range of baits are registered for use in bait stations, in and around buildings and farm storages (within 2m) or enclosed spaces, e.g. drains. Consult the APVMA for a complete listing of currently registered products.

Ideally, mouse bait should be used in dry conditions to achieve maximum ingestion. Baiting at the time of sowing, or within 24 hours, is most effective for protecting recently sown crops. Damage is most severe for about two to three weeks after crop emergence and again around seed-set.

Monitoring is the only method of establishing if further baiting is required. After baiting, mouse activity should continue to be monitored and rebaiting should not occur for at least 14 days. After 14 days reassess mouse activity and if numbers remain high then reapply.

Proactive mouse baiting program looks to control numbers up to 6 weeks prior to planting. If number persist then baits can be reapplied before the crop is planted and further reduce any potential damage to the crop emergence.

Zinc phosphide bait will tolerate some rain, but rain action erodes the bait quality, so rebaiting may be required if rainfall occurs within 1-3 days of baiting.

Based on current research, GRDC is advising growers to bait strategically rather than frequently, and a number of growers have modified farm machinery,  to distribute bait quickly and widely. (Read about Seeder-mounted mouse bait spreaders here)

Growers have modified a variety of farm machinery to apply the 1 kg/ha of zinc phosphide bait required to control the mice present in their fields. Some examples are as follows:

In Victoria, Brad Plant at Manangatang (story available via this link) has built a mouse bait spreader that is ground-driven via his air commodity cart, with a keyless drill chuck and drill bits used to modify the application rate. Product is metered into the air-stream and blown out to a swath width of around 16m.

Griffith, NSW farmer Michael Pfitzner has adapted a ‘whale-tail’ spreader with bait product metered from the air commodity cart and the product drawn into a fabricated plenum mount for the whale-tail, which draws product in a venturi style.