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Blue oat mites and redlegged earth mites

Blue oat mites and redlegged earth mites have been detected in low numbers at a few localities in southern Victoria, and will soon be hatching in other parts of Victoria and New South Wales. Researcher, Aston Arthur (University of Melbourne), says mites have recently been observed along roadsides and within pasture paddocks north of Melbourne and near Geelong, in the Central district of Victoria. Hatching of earth mites has been somewhat delayed this autumn due to the dry, mild conditions experienced in the last 4-6 weeks. Researcher, Garry McDonald (cesar), says hatching from over-summering diapause eggs occurs after sufficiently cool and wet conditions. For redlegged earth mites this is typically after 10 days <20°C and >5mm rain. A substantial rainfall event (i.e. 10mm or more) at the moment is likely to be the catalyst for wide-scale hatching.

Growers are encouraged to check seedling crops over the next few weeks. Blue oat mites (Penthaleus spp.) and redlegged earth mites (Halotydeus destructor) attack a wide variety of plant types including cereals, oilseeds and pastures. They feed by piercing plant cells and sucking out the contents, which results in silver or white patches. High mite populations can kill plants at emergence, when crops are most vulnerable to attack. Autumn insecticide sprays for redlegged earth mites and blue oat mites should ideally target mites 2-3 weeks after emergence. This provides time for the majority of diapause eggs to hatch, but should be before the second-generation eggs have been laid. Be aware, continual monitoring of mite populations is needed and some damage to emerging plants may have already occurred by the time sprays are applied.

Redlegged earth mites and blue oat mites are up to 1 mm in length with a globular shaped dark body and eight red legs. Blue oat mites can be distinguished from redlegged earth mites by the presence of a characteristic orange-red mark on their back. Redlegged earth mites have a completely black coloured body. Before deciding on the most appropriate control measure, ensure the correct mite species has been identified. For assistance with identification download the GRDC Back Pocket Guide - Crop Mites.

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