We are seeing a number of wheat and barley samples with virus-like symptoms right now. The cool, wet spring weather highlights symptom and virus titer. Symptoms will diminish with consistently higher temps, but the virus will still be in the plants. One virus that has been confirmed is Soil-borne Wheat Mosaic (SBWMV). The following is information on this disease of wheat.
Soil-borne Wheat Mosaic Virus (SBWMV) is also called Wheat Soil-borne Mosaic Virus. The virus is vectored by the soil fungus Polymyxa graminis. Symptoms include fields with large irregular areas of chlorotic yellow, stunted plants, especially in low, wet areas. Leaf symptoms are small “green islands” or mottle, with some overall yellowing. Optimal temperatures for symptom development and virus increase are about 60 F (less than 18 C). When spring temperatures warm up to consistently above those levels, symptoms will diminish, but the virus will remain in the plants. Increased tillering and stunting may lead to yield loss, especially in cool wet spring weather. The fungus usually transmits the virus in moist soil in the fall. The virus is not seed or insect borne. WSBMV may be found also on barley, rye and some bromegrass. Management becomes a problem due to the survival of the virus and fungus vector in soil for long periods of time. Areas should be delineated, and plowing (movement of soil) should not go from those areas uphill to clean areas. Resistant wheat varieties are available, and late planting in the fall may be effective in reducing infection.
Photo and information from Nancy Gregory, Extension Plant Diagnostician, UD.