Understand the potential yield losses associated with high mice populations.
- Damage is most severe for about two to three weeks after crop emergence and again at flowering/early seed-set. However, mice will sometimes cause substantial damage to tillering cereals.
Assess the costs and benefits of taking preventative action.
- The cost of preventing a build-up in mice numbers early in the season should be weighed against the savings of non-action. Some preventative actions include controlling summer weeds, removing weeds along fencelines, baiting within 24 hours of sowing to protect seed. Costs include the opportunity cost of the cost of baits, costs of weed control and potential risk of resistance build up. Only consider additional costs specifically for mice, e.g. not costs of weed control if you were going to do it anyway.
Compare the costs, benefits, and risks of each management option against doing nothing.
- What are the likely outcomes of each management option? When the result of treatment is unknown consider the most likely (expected), as well as the worst and best results from each treatment option.
- When calculating the cost of non-treatment, assess the potential risk of yield losses.
- When comparing control options, consider both current and the possibility of further treatment costs. Rebaiting is more effective than increasing rates, but will obviously add to the cost of control.
- Consider costs and benefits for both ground and aerial application methods.
- Consider choosing a treatment option where the expected return is sufficient to offset its risk of the treatment. We all have different attitudes to risk when making decisions. The probability (risk) of outcomes can be affected in terms of responsiveness (efficacy), application rates, products, application methods, treatment costs, climatic conditions and crop prices. The economic calculator can assist with this decision.
Consider risk and associated costs or savings of delaying treatment.
- To avoid unnecessary baiting, regularly monitor mice numbers at several sites to gain true representation of population size.
- Significant yield losses can occur during all stages of crop growth.
Consider the potential risk of re-invasion and costs of further treatment.
- Monitor paddocks post-baiting because if populations are high, mice may move back into the paddocks from adjacent, unbaited areas, normally within a week. If any ‘hot spots’ are discovered, re-bait these areas. The existing zinc phosphide label allows for re-baiting every two weeks if necessary. Baiting maturing crops is effective but kill rates may be substantially lower (around 40–50%).
Ignore all previous treatment costs in assessing current management options.
- Costs associated with previous treatments should be ignored as they are ‘sunk costs’ and will have no bearing on the economic outcome of an option taken now, i.e. even if the current treatment results in the crop not breaking even, provided the additional benefit of the treatment is greater than the cost, the economic gain from treatment will still be better than doing nothing.
Aim to keep pressure on mouse numbers by managing grain and weed seed residues at harvest to limit costs associated with mouse damage in the following season. Weigh up the costs and benefits associated with the following management actions:
- Set harvesters to minimise grain loss.
- Harvest before crops are overripe and pod shatter or grain loss occurs.
- Minimise grain loss with sieve settings and harvester speed.
- Do not leave strips of unharvested grain.
- Use chaff carts or other forms of harvest seed management.
- Clean up any grain spills in and around field bins, augers, silo bags and other grain stores.
- Remove or reduce potential cover including plant material and rubbish around buildings, silos and fodder storage.
- Graze residues and weeds immediately following harvest but leave enough ground cover to minimise erosion.
To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool