Wheat streak mosaic virus and the wheat curl mite

Continual monitoring of wheat crops by the NSW Department of Primary Industries has detected wheat streak mosaic virus (WSMV) this season. The virus has been detected in a wheat crop north of Dubbo. The crop had an affected plant about every 10m with healthy plants in between. In the previous 7 years the paddock had been sown to lucerne. The seed sown this year was harvested from a nearby paddock which had isolated patches of suspected WSMV in 2005.

Carrier of the WSMV, the wheat curl mite (Aceria tosichella) has been observed in high numbers on infected plants. The wheat curl mite can directly damage young growth through feeding, and is also responsible for the transmission of another important disease of wheat, the high plains virus. The wheat curl mite acquires the virus when it feeds on infected plants. Chemical control of the wheat curl mite is believed to be largely ineffective as they live (and are protected) within leaf whorls. Research is underway to better understand the biology of the wheat curl mite and its association with plant viral diseases. 

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. WSMV affected around 5000ha of wheat in the high rainfall zone of NSW in 2005.

Plant pathologist, Gordon Murray (NSW DPI) says crops will be closely monitored across several districts, including Dunedoo, Coonabarabran, Barraba and Wagga Wagga. The distribution and incidence of plants exhibiting WSMV symptoms will be determined throughout the season.