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Earth mites

Agronomist, Phillip Gray (AGnVET), has observed blue oat mites (Penthaleus spp.) attacking a wheat crop near Trundle, in the Central West Slopes and Plains district of New South Wales. The mites have caused some damage to plants, with the leaves showing signs of silvering and white discolouration. Phillip reports that the mite numbers and level of damage have decreased considerably over the last two weeks. Agronomist, Warwick Nightingale (Delta Agribusiness), also reports high numbers of blue oat mites attacking a wheat crop near Jerilderie, in the Riverina district of New South Wales.

Contract Services Manager, Stuart McColl (BCG), has reported high numbers of redlegged earth mites (Halotydues destructor) attacking canola south of Rapunyup, in the Wimmera district of Victoria. The mites are moving into the canola from neighbouring pasture, which is heavily infested with mites. Redlegged earth mites have also been found in a wheat crop about 20 km east of Rapunyup. Stuart says the number of mites was relatively low and there was no significant feeding damage observed.

In most cases, blue oat mites and redlegged earth mites will not cause economic damage to field crops at this time of the season as plants will generally be able to outgrow the feeding damage. However, there is no guarantee and it is recommended that growers continue to monitor crops, particularly younger crops and those under stress. Earth mite feeding in spring can significantly reduce pasture productivity.

A reminder that Timerite® is available during a short window of the season. Timerite® has been shown to significantly reduce mite numbers in spring, leaving few individuals to carry-over to the following autumn. The optimum ‘spring-spray’ dates for redlegged earth mites in eastern Australia are mostly between mid-September and mid-October, and are freely available from the Timerite® website. However, for some regions this window has passed and chemical sprays applied over the next few weeks will be largely ineffective in reducing population sizes next year.

Within pastures, the level of grazing by livestock and quantity of pasture feed on offer (FOO) will impact the size of redlegged earth mite populations. Heavy grazing in spring can help to reduce mite numbers the following autumn. Trials in Western Australian have shown that pastures grazed to 1.4t/ha FOO during spring will result in low levels of mites, and that spraying pastures in spring will have little benefit.

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