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Earth mites

Redlegged earth mites (Halotydeus destructor) and blue oat mites (Penthaleus spp.) continue to cause growers in Victoria and New South Wales problems in emerging crops. In many paddocks, insecticide seed treatments have not been able to withstand mite attack, and chemical sprays have been required to protect vulnerable crop seedlings.

Agronomist, David Ryan (Independent Agronomy Services), has reported finding very high numbers of redlegged earth mites across dozens of paddocks in a widespread area around Ballarat, in the Western district of Victoria. Canola, cereals and newly sown pastures have come under attack in recent weeks. David says he cannot recall seeing such high numbers of redlegged earth mites previously. Paddocks that were treated with Timerite last year have reportedly had fewer mites this season. Agronomist, David Watson (AgVise Services), reports unusually high numbers of redlegged earth mites in canola crops around Inverleigh, in the Western district of Victoria. Highest numbers have been found along paddock margins and fence-lines. Insecticide seed treatments, which normally give a small window of control, have not protected emerging seedlings this season. 

Agronomist, Damien Tanner (JSA Independent), has reported widespread issues with redlegged earth mites in the Wimmera and parts of the Western district in Victoria. Very high mite numbers have been observed in canola, cereals and legume crops at Warracknabeal, Nhill, Horsham and Lake Bolac. Most paddocks have been continuously cropped for many years. Damien says blue oat mites have also been observed in many paddocks, often together with redlegged earth mites. In some paddocks, a border spray has been enough to achieve control. However, in many paddocks the mites are evenly distributed and the entire paddock has required spraying. We have received reports that blue oat mites are widespread around Rupanyup, in the Wimmera district of Victoria. Mites have been reported attacking wheat, barley, lentils and canola. 

Similar observations have been reported in the Riverina and South West Slopes districts of New South Wales. Very high numbers of redlegged earth mites have been observed around Lockhart, Wagga Wagga and Albury. 

The large, widespread hatchings of earth mites this season is largely due to the climatic conditions experienced through summer, autumn and early winter. Specifically, a dry summer and ‘clean’ autumn break are conducive to mite survival and population build up – both of which occurred this year. A dry summer period is favourable for diapause egg survival. Wet conditions over summer, particularly paddocks wet to depth, will kill diapause eggs. In order to hatch from diapause eggs, earth mites require a combination of low temperatures and rainfall. Small, sporadic rainfall events 'false breaks' lead to the hatching of some mites; however the majority of diapause eggs do not hatch. These mites can only survive if there is ample green plant material present. In many seasons there are often several false breaks whereby newly hatched mites die. A clean break will result in mass hatchings, as experienced this year in many regions across Victoria and New South Wales.

Refer to PestFacts Issue No. 3 for further information on redlegged earth mites and blue oat mites.

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