Mice

A mice plague is currently impacting growers in central and northern NSW, with significant damage being seen in late maturing summer crops. In southern NSW the population is very sporadic, with some districts worse than others, with significant differences being seen between paddocks on the same property. Mouse bait is very expensive and in limited supply, therefore critical decisions need to be made regarding the risk of damage occurring, plus the potential consequences of that damage.

Damaging mice populations are most likely to be found in paddocks that have been conducive to their breeding and survival during summer and autumn. An abundant source of food from spilled grain, high stubble loads and mild climatic conditions, are the main factors which mice require to breed quickly. Paddocks with the greatest population of mice are generally barley stubbles, followed by other cereal stubbles, with canola stubble having the lowest population. Growers are urged to be proactive in monitoring their paddocks prior to sowing to assess their population levels, rather than assuming there are high numbers everywhere. To assess a paddock, a transect of at least 100-200m should be walked, to count the number of burrows which indicates the number of mice present. Observations while driving or spraying will not be accurate, particularly on paddocks with stubble cover.

When determining the risk of damage occurring, the crop being sown needs to be considered, with canola seedlings being particularly susceptible to mice predation, as canola seedlings will not recover from mice damage. Cereals are much less susceptible to significant damage, though with very high mice populations, significant damage can still occur.

Damage Mitigation

Removal of stubble by burning or cultivation, will have limited short-term effect on the population, as mice can escape the fire and cultivation in their burrows. However, removal of stubble cover can hinder the growth of the mice population through greater predation, increased impact from weather conditions such as the cold and wind, leading to more disease and damage to burrows. The removal of stubble will also make it easier to identify the number of burrows present, plus decisions to determine the necessity of baiting.

Clients with livestock have the potential to dramatically reduce the number of mice simply through grazing stubbles. As the livestock eat spilt grain, weeds and stubble, this will reduce the feed source for the mice. Stock will also compact the soil surface, therefore making it harder for the mice to dig burrows.

Mice bait will cost approximately 8-$10/ha, therefore it should be spread only when necessary. Bait supply constraints may also reduce the ability to spread as many paddocks as desired. For baiting to be most effective, alternative sources of food must be minimised, so that the mice are forced to consume the bait. When high populations of mice are present, the best strategy is to bait 6 weeks prior to sowing, followed again immediately post sowing. The 6 week gap between applications will allow any bait aversion to be reduced. If lower mice populations are present or insufficient bait is available, a single application immediately post-sowing is the most efficient use of bait.

Proactive monitoring post sowing will be necessary to determine if mice are causing damage to crops. If damage is observed, the only option is to reapply bait to the affected areas. If damage is severe enough, re-sowing may be necessary, however the mice will need to be controlled beforehand.