Wheat curl mite & wheat streak mosaic virus

We have received reports that Wheat Streak Mosaic Virus (WSMV) has affected a number of early sown wheat crops around Dubbo, in the Central West Slopes and Plains district of New South Wales. Senior research scientist, David Nehl (NSW Department of Industry& Investment), says several crops have been affected; including some to an extent where they will now be grazed as harvesting would no longer be viable. In addition to this, researcher Adam Miller (cesar), has identified very high numbers of wheat curl mites in samples collected from these affected crops. 

WSMV is thought to be a relatively recent introduction to Australia. In recent years the virus has caused considerable damage to wheat crops in southern Australia, and has been detected in all major cropping regions. Initial signs of infection are light green streaks on leaves, which later develop into discontinuous yellow stripes running parallel to the leaf veins. 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.

WSMV is a particular concern for early sown dual-purpose wheat crops, although it can adversely affect main season wheats as well. Growers are advised to check crops for virus symptoms, particularly in paddocks with a history of WSMV. In previous seasons, symptoms have been apparent from early-winter onwards. Although oats, barley and triticale can be infected with WSMV, they are usually not severely affected.

The wheat curl mite (Aceria tosichella) is the main vector for WSMV. 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 believed to be largely ineffective as they live (and are protected) within leaf whorls.

Wheat curl mites are widely distributed in southeastern Australia and can survive on plants other than cereals. Alternate hosts identified in Australia 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 (which can provide a ‘green bridge’ between seasons) is one of the most practical methods to reduce the build-up of mite numbers and the risk of WSMV transmission. David says it appears that a significant ‘green-bridge’ present at the time of sowing (Feb-March) has lead to the situation seen here. 

C lick here for further information on the wheat curl mite and WSMV, and click here to report a recent detection of WSMV.