North Dakota State University in Fargo is getting reports of the wheat streak mosaic virus in winter wheat in the central and southwest regions of North Dakota, according to university plant pathologist Marcia McMullen. She recommends that producers who are suspicious of it in their crops test it immediately.
"Most farmers are fairly familiar with the symptoms. But they can get confirmation if they aren't sure," she says. "Our plant diagnostic lab at NDSU has a little test. We get the plant one day, we can get the results the next day."
She says the lab needs at least six to eight leaves that show the characteristic pale yellow streaks along the blade.
Wheat streak mosaic is a viral infection of the plant that's transmitted by the wheat curl mite. McMullen suspects that the winter wheat probably was infected last fall, when the wheat curl mite, the carrier, moved to it from volunteer wheat.
"The mite is always looking for green tissue, and in that process, it's moving and transmitting the virus more readily," she says. "Also, it's often associated with winter wheat production because it survives in the crowns over winter."
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The mites also overwinter in perennial grasses and use the wind to move from an infected plant to a healthy one, she says. The symptoms in winter wheat are becoming more apparent now because of recent dry weather in the western part of the state.
"It is something we see more in year when we have dry conditions and the plants are stressed," she says. "The mite isn't continually reproducing and feeding, and when it feeds, it transmits more virus. But if it's cool and wet, it's kind of staying hunkered down in the crown, and it's not feeding or reproducing as fast, and the plant is sending out new shoots, just keeping ahead of it."
Damage can be minor, if conditions are cool and wet. But if they turn hot and dry, as western North Dakota has been the past few years, it can have direct economic effect on farmers' bottom lines. There are no insecticides or viruscides available to control the mite or the disease.
"What we're recommending right now is that growers who have positive confirmations of this viral disease make a decision," McMullen says. "If it's severe enough, should they defer the winter wheat crop and replant -- and that window is getting pretty short."
