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Wheat streak mosaic virus and wheat curl mites

Agronomist, Graeme Callaghan (Graeme Callaghan & Associates), has reported a number of early sown wheat crops affected by Wheat Streak Mosaic Virus (WSMV) around Coonamble and Warren, in the Central West Slopes and Plains district of New South Wales. Graeme reports that the affected crops appear to be adjacent to areas that contained summer grasses.

WSMV has been detected in all major cropping regions of Australia. In previous years, symptoms have been apparent from late August onwards. Plants infected with WSMV initially have light green streaks on the leaves which later develop into discontinuous 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. WSMV is a particular concern for early sown dual-purpose wheat crops, although it can also adversely affect main season sown wheats.

WSMV is primarily spread by the wheat curl mite (Aceria tosichella), although low level transmission can also occur through infected wheat seed. Wheat curl mites typically colonise the youngest tissue of a wheat plant and acquire WSMV when feeding on infected plants. Chemical control of mites is believed to be largely ineffective as they predominantly live (and are protected) within leaf whorls. Graeme reports wheat curl mites present in the affected crops.

The wheat curl mite is widely distributed in south-eastern Australia, including Tasmania, 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. At this stage, controlling these host plants (which can provide a ‘green bridge’ between seasons) is likely to be one of the most practical methods to reduce the build-up of mite numbers and the risk of WSMV.

For further information on the wheat curl mite and WSMV, click here.

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