Blue oat mites

Blue oat mites occurred particularly early this year, and continue to place establishing crops and pastures under pressure.

 

Where have they been reported?

We have received a number of reports of blue oat mites, particularly in crops and pastures in the Northern Tablelands of NSW. In Oakwood, Graman and Gragin, the mites have had a significant impact on oats and wheat from April onwards. Numbers have varied from 3-4 per plant and warranted chemical control. Blue oat mites have also been in much larger numbers than usual on canola crops and pastures east of Mudgee. In Victoria, blue oat mites have been active for several weeks across all districts, mostly reported from pastures and cereal crops.

Blue oat mite habits and behaviour

Blue oat mites (Penthaleus spp.) are the most abundant earth mites in many cropping and pastoral areas of Victoria, Tasmania and New South Wales. There are three species of blue oat mites which attack emerging pastures, canola and cereal crops. Their feeding causes silvering or white discoloration of leaves and distortion or collapse in severe infestations. Affected seedlings can die at emergence with high mite populations. Like redlegged earth mites, blue oat mites survive hot and dry summer conditions as eggs, which hatch in autumn following suitable conditions. These conditions appear to be different to those required by the redlegged earth mite. In addition, unlike redlegged earth mites, blue oat mites typically feed singularly or in very small groups. Plants will often outgrow mite-feeding damage when the conditions are favourable, which is the case in many regions this season.

Our advice

It is critically important to distinguish pest mite species. Blue oat mites and redlegged earth mites differ markedly in their biology and tolerance to insecticides, and so require separate management strategies. The three pest species of blue oat mite also differ in their biology but look identical to the eye. Penthaleus falcatus, for example, is more often found on canola and is more tolerant to some insecticides than the other Penthaleus species.

Control options

If chemical control is warranted, blue oat mites should be targeted within 2-3 weeks of emergence to protect newly germinated seedlings, which are most prone to mite attack. This approach will also target mites before they reach the adult stage and have a chance to lay winter eggs. Insecticide seed treatments will also offer some (but not complete) protection to emerging crops, however growers are encouraged to monitor paddocks while crops remain at the seedling stage. Weed control will suppress the build-up of blue oat mites during the growing season.

Description

Blue oat mites can be distinguished from other mites by their blue-black coloured body and characteristic red mark on their back. They are often mistaken for redlegged earth mites due to their similar appearance and sympatric life cycle. A microscope is required to distinguish the morphological differences between Penthaleus major, Penthaleus falcatus and Penthaleus tectus.

For assistance with mite identification download the GRDC Back Pocket Guide - Crop Mites. For images of blue oat mites, click here.

 

*Sources of field reports of blue oat mites

Damien Barri – Grower (Central Victoria)

Josh Douglas – Researcher, The University of Melbourne

Rachel O’Neill – Agronomist, Landmark (NSW Central Tablelands)

Candice Robertson - Agronomist, Landmark (NSW Central Tablelands)

Phil Stoddart – Consultant (NSW Central Tablelands)