Author: Natalie Lee, GRDC
Date: 1st April, 2019
Western Australian grain growers are encouraged to assess mouse numbers on different parts of their properties if they suspect mice could pose a risk to crops at sowing.
High mouse numbers have been reported in localised parts of the Geraldton port zone, including areas in Binnu, Ogilvie and Mullewa.
Mice may also be present at potentially damaging levels in other areas, especially where there is a reasonable supply of food from grain being left on the ground, or thick crop residues providing shelter.
CSIRO researcher Steve Henry said mouse numbers could be highly variable across a region, with different levels of activity occurring even between paddocks, and heavy crop stubbles could hide mouse activity.
“It is therefore important that, in the lead up to seeding, growers get out of their vehicles to assess mouse activity, rather than just driving across paddocks,” he said.
“Walk about 30 metres in from the edge of the paddock and set a 100 metre by one metre wide transect (100 square metres), following the furrows, and record the number of mouse burrows that look active. Repeat this across two to four transects in larger paddocks.
“If there is an average of one burrow per 100 square metres, there will be about 100 burrows per hectare. Assuming there are about two mice per burrow, growers should consider baiting because the threshold for economic damage at sowing is 200 mice per hectare.”
Mr Henry encourages growers and advisers to report and map mouse presence, absence and level of activity using the MouseAlert website so others can see the scale and extent of localised mouse activity.
Broadscale application of zinc phosphide bait is the only method available to growers to control mice in their paddocks.
Mr Henry says timely application of bait at the prescribed rate (one kilogram per hectare) – not more or less – is paramount for reducing the impact that mice have on crops at sowing.
“Strategic use of bait is more effective than frequent use of bait,” he said.
“When baiting at seeding time, baits should be applied directly following sowing – such as by using a spreader on the back of the seeder – as the mice eat the baits on the surface in preference to digging up the planted seed.
“Baiting more than 48 hours after sowing will be less effective as mice can dig up and eat a lot of seed within this short period.”
CSIRO researcher Steve Henry says mouse outbreaks can be localised between farms, and even within farms, and heavy crop stubbles could hide mouse activity. Photo by GRDC.
Mr Henry said that if the first bait application was at sowing time, growers should monitor mouse numbers following seeding and, if rebaiting was required, wait six weeks after the first application to overcome bait aversion by mice.
He stressed the importance of regular monitoring as mouse populations could increase or decrease rapidly depending on conditions and result in crop damage throughout the growing season.
“It can be difficult to correlate mouse numbers prior to seeding with crop damage, but once mouse numbers are very high it is very difficult to reduce damage to crops and control strategies can be costly,” Mr Henry said.
He said anecdotal reports suggested mice could be more damaging to freshly sown canola crops than cereal crops, as feeding by mice was more likely to kill the young canola plants.
“It can be advisable to graze livestock in areas where there are high mouse numbers to reduce mouse food sources in the lead up to seeding, particularly where canola crops will be sown into cereal stubbles,” Mr Henry said.
Year-round paddock and farm hygiene practices are key to minimising the availability of quality food to mice.
Mouse management strategies and advice are outlined in the GRDC GrowNotes™ Better Mouse Management Tip and Tactics fact sheet.
Other resources are available on the GRDC Mouse Control hub on the GRDC website.
In response to the increasing prevalence of mice in many key grain growing regions of Australia, the GRDC last year injected a further $4.1 million into mouse control research, development and extension (RD&E) initiatives.
Current research outcomes from GRDC mouse investments, including bait substrate trials, are available in a GRDC Grains Research Update Paper