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Words by Alan Meldrum

Controlling mice is becoming an important issue in WA. Rarely does WA suffer the types of plagues seen regularly in the eastern states. After a rise in mouse sightings and some baiting through 2021, and off the back of one of our best ever grain production seasons, mouse numbers are on the rise and are posing a threat to growers in most districts.

The Liebe group’s AgChat series, sponsored by GrainGrowers, last week featured mouse control with the CSIRO’s mouse expert Steve Henry. Steve undertook an extensive talking tour through the northern districts with GRDC to talk about how to monitor mouse numbers, control measures and ongoing research on this persistent pest.

Dylan Hirsch hosted this Liebe AgChat event at his farm at Bunjil. In his paddock with fully cut stubble and stripper stubble, it was easy to find mouse holes. Steve explained that 2 active holes in a 100m transect equalled 400 mice per hectare. With each generation taking just 3 weeks, the numbers can explode quickly prior to winter.

Autumn control is the optimum time for control as winter cold slows the mice population and mice don’t do well on green material. For mice, grain is the game. Minimising their population before spring is critical.

The key points for mouse control are:

  • Heavy residue cover is favoured by mice over a sparsely covered paddock. Look in those paddocks first.
  • Monitor mouse numbers by walking a paddock and using chew cards. Baiting is expensive so you want to know it is needed.
  • Check for active mouse holes by spreading corn flour around the entrance to see tracks
  • Spread bait within 48 hours after seeding and always after rain. This gives the mice the best chance to find the bait after a machine pass. Rain can dilute the bait so after a rain front is better than prior.
  • Bait is spread at the rate of 2-3 grains/m2. A ute-based spreader is very effective, but almost any machine can have a spreader attached to avoid another pass over the paddock. Aerial spreading is also practicable.
  • Perimeter baiting is ineffective.
  • Predators will NEVER be able to control mouse numbers. They will however be unaffected by the bait should they consume a poisoned mouse.
  • Threshold numbers, to help you decide on the need for control measures, aren’t available. Further research is needed to define them.
  • Growers should talk to their agronomists and suppliers early regarding mouse control options and plan ahead to secure desired quantities of required chemistries.