Wheat streak mosaic (WSM), caused by Wheat Streak Mosaic Virus (WSMV), is a common disease in many wheat growing regions in the U.S. and world. This is one of the few wheat diseases that can cause a total loss, although losses typically are much less. WSMV survives only in living plants: wheat, corn, and many other grasses. WSMV is transmitted by the wheat curl mite (Aceria tosichella), which also transmits the High Plains Virus; both viruses can be present in affected plants.
WSM symptoms vary based on the virus strain, the wheat variety, how old the plant was when it was infected, and weather conditions. Typically, infected plants are stunted, may be splayed on the ground, and do not tiller as well as unaffected plants. Foliar symptoms include a light green to yellow mottled mosaic; more advanced infections may develop yellow streaks running parallel to the veins. Tightly rolled and trapped leaves may also be evident and are the result of feeding damage that occurs when large numbers of wheat curl mites are present.
In winter wheat, plants can be infected in fall or spring, but symptoms usually begin to appear in spring as temperatures warm. Symptoms are less pronounced and can be difficult to discern when temperatures are less than 70°F but become more pronounced as temperatures increase. Symptoms are similar in spring wheat but progress more quickly.
The wheat curl mite can feed on many different plants including wheat, corn, and other grasses such as barnyardgrass. Wheat streak mosaic is favored when volunteer wheat is present because it allows both the wheat curl mite and virus to reproduce, and by longer and warmer fall temperatures that allow the mite to spread the virus from volunteer plants to the newly planted winter wheat crop. Wheat curl mites spread by wind and consequently, wheat streak mosaic typically starts along field borders as mites move into the field. Because wheat curl mites require living plants to survive, they move from maturing small grain crops, corn, or weedy hosts to nearby green hosts. As a result, the disease is more common in areas where spring and winter wheat overlap, a situation known as the “green-bridge.” Early planted winter wheat is particularly susceptible as the mite can move in from late-maturing wheat and corn crops and volunteer plants or grassy weeds into the newly planted crop as it emerges.
WSM can be confirmed by submitting a sample to the WSU Plant Pest Diagnostic Clinic, where presence of WSMV, as well as other wheat viruses, can be confirmed. Directions for submitting samples is available on the WSU Plant Pest Diagnostic Clinic website.