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Earth mites

Consultant, John Robertson (Agwise Services), has reported blue oat mites (Penthaleus spp.) causing damage to several canola and vetch crops around Nhill and Rainbow, in Mallee district of Victoria. John says canola plants at the 3-4 leaf stage were severely affected, and chemical control was required to prevent further damage. Unusually high numbers of blue oat mites have been observed in many regions this season. Researcher, Aston Arthur (The University of Melbourne), has reported very high numbers of redlegged earth mites (Halotydeus destructor) in a pasture paddock north of Kerang, also in the Victorian Mallee. Aston says mite numbers have started to increase as temperatures have become milder over the last few weeks. Aston estimates mite numbers are > 2000 per m2, and expects these to increase through September, which is typical of earth mites (and lucerne flea), which generally have a spring ‘peak’ in population size.

In most cases, earth mites will not pose any further problems this season as crops and pastures will generally be able to outgrow the feeding damage. However, it is recommended that growers and advisers monitor younger crops, particularly those under stress.

Early spring is the ideal time to think about potential mite issues for next season. For redlegged earth mites, control can be timed to occur during a short window in spring when mites have ceased laying winter eggs (eggs that must hatch this season) and before they start laying diapause eggs (over-summering eggs that survive until next season). This approach, known as Timerite®, can significantly reduce redlegged earth mite numbers the following autumn.

The optimum ‘spring-spray’ dates for redlegged earth mites in eastern Australia are mostly between mid-September and mid-October, and are freely available from the Timerite® website. Some examples of the recommended dates are: Swan Hill - 12th Sep, Horsham - 23rd Sep, Bendigo - 28th Sep, Wagga Wagga - 29th Sep, Dubbo - 14th Oct, and Colac - 16th Oct.

The date is based on geographical location and is therefore unique to each property. It is recommended that spraying be carried out within the two-week period before the optimal date. The use of Timerite® should be considered in paddocks where redlegged earth mites are a continual problem.

Correct identification of mites before deciding to spray is important. Timerite® is designed to only control redlegged earth mites; it will not effectively control other pests, such as blue oat mites. Before using this approach, consideration should also be given to the actual number of mites present and the susceptibility of the crop to be sown next season. Insecticides need to be used carefully to avoid resistance issues, which have already emerged in the redlegged earth mite in Western Australia.

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