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Wheat streak mosaic virus

Growers should remain on the look out for wheat streak mosaic virus (WSMV) in wheat and barley crops this year. Although no confirmed cases of the virus have been reported this season so far, symptoms of the virus are likely to become more obvious as wheat plants mature heading into spring. Plants infected with WSMV initially have light green streaks on the leaves, which later develop into yellow stripes running parallel to the leaf veins. 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.

The primary vector of WSMV is the wheat curl mite, Aceria tosichella. 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 outside of the growing season is one of the most practical methods to reduce the build-up of mite numbers and the risk of WSMV in emerging crops.

As part of a GRDC funded research project, Dr Adam Miller (University of Melbourne) is providing a free WSMV genetic screening service for growers this season. If you wish to utilize this free service please send suspect wheat specimens (3 plants maximum) by express post to: Adam Miller, Hoffmann Laboratories, The University of Melbourne, BIO21 Research Institute, 30 Flemington Road, Parkville, 3010, Victoria.

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

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