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.