Due to the cool temperatures during April and May, wheat spindle streak mosaic virus symptoms have appeared in wheat fields, and in many varieties the symptoms are quite severe. The fungus invades the roots of wheat plants and transmits the virus.
Most infections occur in the fall, and symptoms develop in the spring when the plant resumes growth.
The soil may remain infested for at least five years, and probably much longer. Early symptoms appear as yellow or bright green dashes and streaks in mildly effected plants and as bright yellow-green mottling in more severely affected plants. The dashes and streaks are oriented parallel to the leaf veins and taper at both ends to form spindles. Symptoms are first evident on lower leaves and may develop on new growth under favorable conditions. Symptoms develop most rapidly between air temperatures of 48oF and 60oF. When cool temperatures persist into late May and early June, symptoms may appear on all leaves, including the flag leaf.