The importance of spotting the difference between blue oat mites and redlegged earth mites

Blue oat mites are active now and it’s critical to distinguish them from redlegged earth mites before deciding on the most appropriate management 

Where have they been reported?

A sizeable blue oat mite (Penthaleus spp.) population has been reported in an oat, ryegrass and clover pasture in Colac, South West Victoria. Further populations have been observed in Victoria, including the Mallee, and between Albury and Rutherglen in the North East. Blue oat mites have also been reported in emerging canola in the NSW Riverina district, and are undoubtedly active in many more regions.

About blue oat mites

Adult blue oat mites are approximately 1 mm in length, have a blue-black body with 8 red-orange legs, and can be distinguished from redlegged earth mites (Halotydeus destructor, RLEM) from the distinctive red mark on their back (an anal shield). While both mites are pinkish-orange with six legs soon after hatching, the blue oat mite transitions from brown to green prior to adulthood, whereas RLEM develops their characteristic velvety black body as nymphs.

A blue oat mite with distinctive red mark on its back (left) and RLEM with velvety black bodies (right) (Source: cesar)

 

A microscope is required to distinguish the morphological differences between Penthaleus major, Penthaleus falcatus and Penthaleus tectus, which look very similar to the naked eye. These species differ in their distributions, pesticide tolerances and host plant preferences.

Our advice

A number of chemicals are registered in pastures and crops. However differences in tolerance levels between species complicates management of blue oat mites. In particular, P. falcatus, which is mainly found on canola, has a higher tolerance to a range of pesticides and this is often responsible for apparent chemical control ‘failures’. Ensure pesticide sprays are applied at the full registered rate when targeting blue oat mites in emerging canola crops. P. major and P. tectus have lower tolerances to pesticides and are more easily controlled.

For low-moderate mite populations, insecticide seed dressings are an effective control method. Avoid prophylactic sprays; apply insecticides only if control is warranted and if you are sure of the mite identity. If chemicals are used at or after sowing, it is best to apply within three weeks of the first appearance of mites, before adults commence laying eggs. Spring spraying using TIMERITE® (as is recommended with RLEM) is largely ineffective against blue oat mites and is not recommended. This is because the mites use a varied or different set of cues to that of RLEM for the initiation of diapause egg production.

Click here for more comprehensive information on blue oat mite, including their occurrence, lifecycle, behaviour and management strategies

 

Sources of field reports of blue oat mites

Josh Douglas – Researcher, University of Melbourne

Warwick Nightingale – Agronomist, Delta Ag (Riverina NSW) 

Andrew Powell – Agronomist, Davies and Rose (Central Victoria)

John Stuchbery – Agronomist, AGRIvision Consultants (Victorian Wimmera)