Diagnosing wheat streak mosaic virus
Wheat streak mosaic virus (WSMV) is a seed and mite-borne virus that infects cereals (including wheat and barley) and grasses. WSMV is spread by the wheat curl mite (WCM) and requires a green-bridge to survive between growing seasons. Substantial yield losses are likely if infection occurs early.
What to look for
- Yellow stunted plants in patches, scattered on the edge or within the paddock.
- Symptoms are less obvious in winter. The virus spreads with warm weather in autumn and spring when mites build up and they move between plants.
- Symptoms are seen in warm growing conditions, generally before June or from early spring.
- Wheat is the most important host of WSMV and all varieties are susceptible.
- Leaves of newly infected wheat plants have broken yellow stripes that join together as the plant ages to be pale yellow streaks. In older leaves, yellowing is toward tips.
- Barley is less severely affected than wheat and varieties differ in their susceptibility to infection.
- Barley leaves have necrotic flecks and pale green streaks with older leaves showing yellow along the length.
- Early infected wheat and barley plants are stunted with multiple tillers and have seed heads that contain shrivelled or no grain.
What else could it be
|Diagnosing yellow dwarf virus||Yellow interveinal chlorosis leaf streaks||WSMV has less vivid stripes. WSMV affect younger leaves causing broken stripes that join as the leaf ages.|
|Diagnosing zinc deficiency in wheat||Stunted plants with many tillers and striped leaf lesions||Zinc deficient plants have pale linear spots or lesions that can develop into parallel 'tramlines' and they lack vivid yellow streaks towards the leaf tip.|
Where did it come from?
- The wheat curl mite that spreads WSMV is tiny and can only be seen with a microscope. They survive on self-sown cereals and grasses, and thrive in warm conditions (25-28°C).
- During seasons of late summer and early autumn rainfall large populations of the mites can develop on 'green bridge' hosts and then move to infest autumn sown crops.
- Sowing infected seed produces virus infected seedlings from which mites can pick up the virus and spread it to other plants.
- Seed infected with even very low levels of the virus can cause significant yield losses as infection is able to take hold early in the season.
- There is no treatment after plants are infected. To minimise infection:
- Control 'green bridge' volunteer cereal plants and grass weeds as they harbour both WSMV and WCM. This needs to be done 1 month prior to sowing.
- Sow clean seed.
- Avoid early seeding in virus risk conditions, such as seeding directly into a recently sprayed out 'green bridge' or using infected seed, as warm seasonal conditions during autumn favour high wheat curl mite populations.