April 28, 2006
Figure 1. A wheat field near Auburn showing widespread symptoms of yellowing and stunting, |
Figure 3. Chlorotic streaking on leaves of a wheat plant infected by wheat streak mosaic virus. Photo credit: John E. Watkins |
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Figure 2. Symptoms of virus infection (mosaic and stunting) on a wheat plant in a field near Auburn, |
During the last few weeks there have been reports of yellow wheat in fields. In some fields the wheat is also stunted. In a field near Auburn, yellowing and stunting was observed in the entire field on April 18 (Figure 1). Previous crops in this field were corn and soybean. Examination of leaves on individual plants revealed mosaic symptoms typical of virus infection (Figure 2). Samples from the field tested positive for both soilborne mosaic virus and wheat streak mosaic virus. At least one other sample submitted to the Plant and Pest Diagnostic Clinic from a different location in eastern Nebraska has also tested positive for wheat streak mosaic.
Cause
Wheat streak mosaic is caused by wheat streak mosaic virus, a member of the Potyviridae family. The virus is transmitted by the wheat curl mite. The mite survives best on wheat but can also survive on several weedy grasses. Wheat streak mosaic can cause up to 100% yield loss depending on time, extent of infection, virus strain, cultivar susceptibility, and environmental conditions.
Infection
Infection of fall-sown wheat occurs mainly in the fall and is dependent on survival of the wheat curl mite on preharvest volunteer wheat and other grass hosts until wheat has emerged. Preharvest voulunteer wheat emerges usually after a hail storm at the soft dough stage. The mites move onto the emerged wheat to feed and transmit the virus in the process.
Symptoms and disease spread
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Infected leaves show chlorotic parallel streaks (Figure 3). Leaves become mottled yellow as symptoms progress. Stunting and rosetting occur if plants are infected early (early tillering or before). Symptoms appear in the spring and become more severe as the temperature rises. The optimum temperature range for mite reproduction and virus replication in the plant is 75-81oF. Disease spread and distribution in the field depends on spread of the wheat curl mite, which is carried by wind. Symptoms can be localized along field borders or can be widespread throughout the field (Figure 4).
Management
There is no cure for wheat streak mosaic. The best strategy for disease management is prevention. The following cultural practices can help to prevent infection. Avoid planting earlier than the recommended date for your area. Control preharvest volunteer wheat and grass weeds that support populations of the wheat curl mite. Volunteer wheat and grass weeds must be dead for at least two weeks before planting to prevent virus transmission to newly emerged wheat. Choose cultivars with tolerance to wheat streak mosaic virus. Do not plant winter wheat next to late maturing corn or oat fields that are still green as they may serve as sources of the wheat curl mite.
Stephen N. Wegulo
Extension Plant Pathologist, Lincoln
Jennifer L. Chaky
Extension Eductor, Lincoln
Gary W. Lesoing
Extension Eductor, Auburn
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