Wheat curl mites & wsmv

A number of Wheat Streak Mosaic Virus (WSMV) detections have been confirmed in New South Wales this season with reports near Dunedoo, in the Central West Slopes and Plains district and around Cootamundra and Tarcutta, in the South West Slopes. Researcher, Adam Miller (cesar), says seed transmission has probably played a role in the emergence of WSMV this year, with infected crops characterised by scattered patches of infected plants. The ‘green bridge’ present in many paddocks over summer, combined with the high number of early-sown crops, has increased the risk of further outbreaks this season. District agronomist, Paul Parker (I&I NSW), advises that growers should begin scouting crops for virus symptoms, particularly in paddocks with a history 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. These symptoms can sometimes be confused with nutritional, environmental and chemical damage. 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. Paul says WSMV symptoms could be masked by the yellowing of leaves observed in many crops this year as a result of nitrogen deficiency caused by excess water in the root zone.

The vector for WSMV is the wheat curl mite (Aceria tosichella). Adult mites are wingless, cigar-shaped, about 0.2 mm long and have two pairs of legs located at the front. The mite’s small size and secretive habits make it extremely difficult to detect even with a microscope. Chemical control of the wheat curl mite is largely ineffective because they live (and are protected) within leaf whorls. They are widely distributed in south-eastern 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.

For further information, and to keep up to date with WSMV detections emerging throughout the growing season or to make a report visit www.wheatcurlmite.org