Wheat Streak Mosaic Virus in Eastern Washington

High plains wheat streak mosaic virus.

Wheat streak mosaic is caused by Wheat Streak Mosaic Virus (WSMV), which is common to many of wheat growing regions in the U.S. and world. Losses from this disease range from minimal to the entirety of the field. WSMV survives in wheat and volunteer wheat crops, 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 an affected plant.

Symptoms can vary based on the virus strain, the wheat variety, and weather conditions. Typically, infected plants are stunted 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 are the result of feeding damage that occurs when large numbers of mites infest the plant. In winter wheat, plants can be infected in fall or spring, but symptoms usually begin to appear in spring. Symptoms are less pronounced and can be difficult to discern when temperatures are less than 70°F; however, the symptoms become more pronounced as spring temperatures warm.  Symptoms are similar in spring wheat but progress more quickly.[row layout=”quarters” ]High plains wheat streak mosaic virus.
Mosaic Mosaic and mottling on leaves of wheat plant infected with both High Plains Virus and Wheat Streak Mosaic Virus.Yellow parallell wheat streak mosaic virus.
Yellow parallel streaking of a plant infected with Wheat Streak Mosaic Virus.Streaking and mosaic associated with Wheat Streak Mosaic Virus infection.Volunteer wheat infect with wheat streak mosaic virus.Volunteer wheat infected with Wheat Streak Mosaic Virus.[row padding_top=”1.5rem” ]The Wheat Curl Mite is able to feed on many different plants including wheat, corn, and other grasses such as barnyard grass. Wheat streak mosaic is favored by conditions under which more 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 the volunteer 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. Wheat curl mite require living plants to survive, so they move from maturing grain crops or weedy hosts to nearby green hosts. Because of this behavior the virus 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 crops and volunteer plants or grassy weeds into the newly planted crop as it emerges.

Disrupting the green-bridge to prevent mites moving into the emerging crop is critical to controlling wheat streak mosaic. Destroying volunteer wheat and other grain or grass crops with tillage or herbicides at least 2 weeks prior to planting is very effective. Grassy weeds should likewise be controlled prior to planting. Avoiding very early seeding and delaying a week or two later than is usual for the area is also effective. There are no chemical insecticides, either foliar or seed treatments, that are recommended for control.

To confirm WSMV a sample must be tested for the virus. The WSU Plant Pest Diagnostic Clinic is available to test plants for WSMV as well as other wheat viruses. To submit a sample visit the WSU Plant Pest Diagnostic Clinic website.

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Wheat leaves showing WSMV.
Wheat leaves showing mosaic and streaking symptoms as a result of Wheat Streak Mosaic Virus infection.

For questions or comments, contact Tim Murray via email at tim.murray@wsu.edu, via phone at (509) 335-7515, or by following him on Twitter @WSUWheatDoc; or contact  Plant Pest Diagnostic Clinic Diagnostician Rachel Bomberger at 509-335-3292 or email Rachel.bomberger@wsu.edu / plant.clinic@wsu.edu.