Earth mites and spring spraying

Agronomist, Tim Sawley (Landmark Townsend), has reported several problems with blue oat mites (Penthaleus spp.) attacking crops in the Merriwa region, in the Upper Hunter Valley of NSW. Penthaleus major have been found attacking several oat crops, while Penthaleus tectus has been identified attacking a wheat crop. These two species of blue oat mite are commonly found attacking cereals, particularly P. tectus.

P. major and P. tectus populations can be suppressed by rotating out of cereals and pastures and into canola, which is a non-preferred host of these two mite species. A reminder, that there are three known pest species of blue oat mite in southeastern Australia. The different species respond differently when treated with pesticides, therefore, correct identification is critical.

Balaustium mites (Balaustium spp.) have been identified attacking a barley crop in the Merriwa region. The affected paddock was pasture last year, and Tim says the numbers are rather patchy across the crop. The damage does not warrant control at this stage, which can be challenging in many instances due to the high natural tolerance of Balaustium mites to chemicals. For information on Balaustium mites refer to PestFacts Issue No. 4.

Redlegged earth mites (Halotydeus destructor) have been reported from a variety of regions in both NSW and Victoria. Most reports in recent times have been regarding attacks on pastures and cereals, although canola and lucerne damage, as a result of redlegged earth mites, have also been reported.

Control of redlegged earth mites can be timed to occur during a short window of the season – during spring - when they 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 autumn).

The optimum ‘spring-spray’ dates for redlegged earth mite control in southeastern Australia are mostly between mid-September to mid-October. Exact dates are available through the Timerite® model, which was developed by CSIRO. Timerite® packages are available free from www.timerite.com.au or by phoning the Australian Wool Innovation helpline on 1800 070 099.

The date for spring spraying is unique to each farm and remains constant from year to year. It is recommended that spraying be carried out within the two week period before the optimal date. Some examples of the ideal date are: Horsham (Victoria) - 23^rd September; Wangarrata (Victoria) - 15^th October; Dubbo (NSW) - 14^th October; and Griffith (NSW) - 14^th September.

Correct identification of mites before deciding to spray in spring is important. Timerite® is designed to only control redlegged earth mites; it will not effectively control other pests, such as blue oat mites.