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Blue oat mites

Agronomist, Greg Toomey (Landmark), has reported a large number of small mites found in a newly sown canola crop near Elmore, in the Northern Country district of Victoria. The mites have been observed on volunteer barely present within the paddock, but not directly on the canola cotyledons. The mites have been identified as blue oat mite (Penthaleus spp.) nymphs. On hatching, blue oat mites are very small, with a pinkish-orange coloured body. They soon darken in colour, becoming blue-black with a distinctive red mark on their back.

There are three pest species of blue oat mite, which differ in their biology, but to the eye look identical. The species responsible for this outbreak has been identified as Penthaleus major. This species primarily feeds on pastures, oats and other cereals. Canola is not a preferred host. Given this, and the fact that the canola seed was treated with an insecticide dressing, these mites are unlikely to cause significant damage in this case.

Elsewhere in Victoria, blue oat mites have been reported from paddocks south of Bendigo, in the Northern Country district, at Rupanyup, in the Wimmera district, Birchip, in the Mallee district, and near Meredith and Ballarat, in the Western district. As reported previously, blue oat mites are already active in many parts of New South Wales.

Blue oat mites attack a variety of crops and pastures, including cereals, oilseeds, legumes and fodder crops. They can also survive on a variety of weeds, particularly broad-leaved weeds. Blue oat mites feed by piercing plant cells and sucking out the contents, which results in silver or white patches. There are several options to control blue oat mites. If using foliar insecticides, these should be applied within three weeks of the first appearance of mites. This will allow for further hatching of blue oat mites from over-summering eggs but will be before mites reach the adult stage and begin to lay winter eggs.

It is important to distinguish blue oat mites from other mite species, such as redlegged earth mites and bryobia mites, as this will influence control. Click here for images of blue oat mites and refer to PestFacts Issue No. 3 for further information.

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