Wheat curl mites

Several unconfirmed detections of wheat streak mosaic virus (WSMV) in wheat crops on the Eyre Peninsula in South Australia should serve as a warning to growers and advisors to be on the lookout for any symptoms of the virus. Although we are currently unaware of any confirmed cases of WSMV in Victoria and New South Wales this season, it is likely that symptoms will increase in crops from now onwards. Researcher, Dr. Adam Miller (University of Melbourne), says this spring may be problematic as good rainfall in the lead up to the season is likely to have favoured the survival of the main vector of this virus, the wheat curl mite (Aceria tosichella).

Adult wheat curl mites are wingless, cigar-shaped, about 0.2 mm long and have two pairs of legs located at the front. The mite’s tiny size and secretive habits make it extremely difficult to detect even with a microscope. They live (and are protected) within leaf whorls, which means chemical control of the wheat curl mite is largely ineffective.

Wheat curl mites are widely distributed in southern Australia and can survive on plants other than cereals. Alternate hosts include barley grass, great brome, annual ryegrass, cocksfoot, black oats, prairie grass, hairy panic, soft brome, wild oats, winter grass and rat’s tail fescue. Controlling these host plants is one of the most practical methods to reduce the build-up of mite numbers and the risk of WSMV.

Plants infected with WSMV initially have light green streaks on the leaves, which later develop into yellow stripes running parallel to the leaf veins. Adam says symptoms can be difficult to detect in young plants and may sometimes be confused with nutritional, environmental or chemical effects. However as plants mature, the signs become more pronounced and affected plants can die prematurely, become stunted or fail to grow. Heads on infected plants can be sterile and contain no seed, or can contain small, shrivelled grain.

For further information, or to discuss a possible virus detection please contact Adam on 0488 735 482 or at admiller@unimelb.edu.au