Wheat Streak Mosaic Virus (WSMV)
Recent research has shown that the virus is seed-borne and this is the most likely explanation of how it entered Australia and then Tasmania. Transmission by seed is at very low levels and therefore is not considered a health risk to a current crop, but it is a source of virus that can build up, via the vector, and eventually find its way to volunteer cereals, weeds and grasses – thereby threatening future crops.
In wheat, the first signs are light green streaks in the leaves and then, as the disease progresses, these become yellow marks resembling a ‘mosaic’ look. These signs can vary somewhat in other susceptible plant species.
Normally, the temperature needs to be above 10°C for the signs to show up, so the disease may not be visible during the winter months.
WSMV symptoms are very similar to those of other health problems, so laboratory diagnosis involving sensitive tests is needed for confirmation.
Grasses and grassy weeds around the edge of newly sown crops can also harbour the mites so these should be controlled as well.
Evidence from overseas, where the disease has been around longer, is that serious crop damage only occurs where there is heavy subsequent infection of early sown crops, and this only happens where there has been a “green bridge” to enable the wheat curl mite to survive in significant numbers from a previous crop.
In areas or seasons where the summer is dry and the sowing break is late, there might be little or no impact.
Tasmania is considered at risk because our summers are milder and moister than cropping areas of the mainland and, therefore, a greater risk of the “green bridge”.
There were serious epidemics of WSMV in wheat crops in NSW in 2005 and 2006 causing crop failure of 5,000 and 20,000 hectares respectively.
All State governments are developing a better understanding of this disease and its incidence around Australia. If you think you have WSMV, you are encouraged to take suspect plants to DPIPWE for identification and advice. It’s important you place any suspect plants in a sealed bag to prevent spread of the disease.
For more information, including help with identification:
Contact: Plant VirologistPeter Cross
13 St Johns Avenue NEW TOWN TAS 7008
Phone: 03 6233 6845
Fax: 03 6278 2716
Tasmania Online | Service Tasmania
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