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By Jordan Hildebrand
Hidden in the stubble of 2019’s wheat harvest, wheat curl mites are moving to find sprouting volunteer wheat seedlings to inhabit and continue the life cycle of wheat streak mosaic virus. The wheat streak mosaic virus (WSMV) instigated by these mites seriously affects the total yield of a wheat crop.
On average, WSMV causes $75 million in losses to Kansas wheat farmers every year. Wheat Streak Mosaic can cause a yield loss of more than 80 percent. WSMV isn’t treatable, but it is preventable. If we take preventative measures now, future yields will improve exponentially.
The virus is spread by the wheat curl mite, which feeds on wheat and other grasses. Wheat curl mites and the virus must have green host tissue to survive on throughout the summer after harvest. They most commonly reside on volunteer wheat that blew out the back of the combine or shattered grain from hail storms that happened before harvest. The mites on the fallen kernels move to the sprouting volunteer seedlings as new plants emerge in the summer.
Volunteer wheat is considered a “green bridge” because it allows the wheat curl mites and the virus to survive the summer.
Losses due to WSMV depend on variety, weather, percentage of infected plants and the time of infection. The first visible symptoms usually pop up in April on the edges of fields near volunteer wheat. Yellow streaking and mosaic patterns on young leaves and stunted tillers are some of the first signs. Symptoms worsen as the weather warms. Leaves on the infected plants turn yellow from the tip down, but usually the leaf veins remain green the longest. This gives the appearance of a striped yellow and green leaf, if the leaf is able to unfurl completely at all.
The best way to prevent the spread of the wheat streak mosaic virus is to remove volunteer wheat and other grassy weeds. Volunteer wheat must be completely dead and dry for two weeks before planting a new wheat crop. Volunteer wheat and other grassy weeds can be killed with herbicides or tillage.
A second management practice to limit the spread of the virus is to avoid early planting. Plant wheat after the “hessian fly free date” for your area. In some areas in western Kansas where there is no Hessian fly-free date, farmers should choose to wait until late September or October to plant their wheat. Planting after these dates will reduce the risk for the new wheat crop and reduce wheat curl mites from moving to new locations of wheat.
In addition, there are a few wheat varieties with moderate resistance to this devastating disease. Hard white wheats Joe and Clara CL, as well as hard red winter wheat Oakley CL have performed well in areas with wheat streak mosaic.
This resistance is not perfect and these plants may still be susceptible to triticum mosaic or high plains mosaic viruses. The resistance to wheat streak mosaic is less effective at temperatures above 75 degrees Fahrenheit. Therefore, planting these varieties early for grazing can place fields at risk for disease-related yield losses.
Undoubtedly, the best method to control WSMV is controlling the volunteer wheat.
Be a good steward, and a good neighbor, when making these management decisions, and you might just be rewarded with a boost in bushels on your next wheat crop.
For more information on controlling volunteer, head to K-State Agronomy’s E-Update resource.