Mouse Management Update

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Mouse numbers in some locations are higher than usual for this time of year, posing the threat of damage to a range of crops leading into harvest.  

Current situation 

  • Favourable conditions have enabled greater mouse survival over winter, particularly in pasture paddocks and other sheltered areas.  

  • Mouse numbers should normally be lowest in late winter, ahead of the main breeding period through spring and summer. 

  • Though variable, higher than normal mouse activity is being reported in northern and central NSW plus the Victorian Mallee. 

Assessment 

  • The best assessment of mouse activity is mouse chew cards. These can be printed from a GRDC template in the link below and used to assess mouse activity, following the straightforward instructions outlined on the template. https://grdc.com.au/__data/assets/pdf_file/0026/307961/Mouse_card_A4web_compressed.pdf  

  • Monitoring burrows can also be performed via walking multiple, 100 metre long by metre wide transects, to count active burrows and estimate an average number of active burrows per 100 square metres, then multiplying by 100 for burrows per hectare. 

  • When assessing crops for damage; cereals will be chewed at the top node, while flowers and/or pods will be chewed in legumes and canola.  

  • Mice can reproduce at a highly efficient rate, particularly in spring when conditions are most favourable, meaning a small population could very quickly become a large problem. 

Spring Baiting  

  • Mouse populations can increase dramatically in spring, so it is important to assess numbers in the paddock and act before significant crop damage occurs.  

  • The latest advice is to apply 1.0 kg/ha Zinc Phosphate (50 gai double the strength of original MOUSEOFF®) bait /kg seed.  

  • 50 gai bait is available under permit and is being stocked by many resellers.  

  • Higher strength bait ensures that all mice are treated with a lethal dose initially, with less aversion to the bait from sub-lethal poisoning. 

  • Baiting crops prior to head emergence of cereals, or podding of canola and pulses, allows mice to receive the bait when little or no alternative food is available.  

  • Applying bait via plane, in swaths, is both effective and efficient. Complete coverage is not essential when bait is the only food available.  

  • At this point in the growing season, it is not critical to use sterilised grain, as the likelihood of germination and harvest contamination is low.  

  • Controlling mice now will help mitigate crop damage through grain fill and harvest, while also reducing numbers leading into autumn 2022. 

Fred Broughton