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Wheat streak mosaic makes troubling fall appearance

Wheat streak mosaic makes troubling fall appearance
Whole fields in Lane and Scott counties wiped out by virus not normally seen until spring.

A fall arrival of wheat streak mosaic in several fields in western Kansas is ringing alarm bells with growers and researchers alike.

Lane County farmer and seedsman Vance Ehmke says he could see it coming as the wet summer and long, warm fall combined to create ideal growing conditions for the volunteer wheat, which provides an intermediate host for the microscopic wheat curl mites that spread the disease to the new wheat crop.

WHEAT STREAK MOSIAC: Severe infestations of wheat streak mosaic disease, a virus introduced by the wheat curl mite, can cause total loss of winter wheat.

"This virus can be extremely dangerous. I have personally seen wheat yield reductions of near 100% in areas of fields adjacent to heavily infected volunteer. Usually, though, you won't see the actual damage until later next spring. If you have symptoms in the fall, you have a real problem. Well, we have a real problem."

Chris Long, Lane County Extension agent, says a farmer east of Dighton had him out to look at a wheat field he suspected was infected. He says the farmer had not planted exceptionally early, but there were big fields of volunteer wheat on two sides of the field.

Long took some samples and sent them to Kansas State University, where the lab confirmed it is wheat streak mosaic.

Long says he had been asked on a number of occasions to get samples in the spring, but this is the first time he has seen heavy infestation in the fall.

Especially troubling, he says, is the fact that the variety in a field he looked at on Nov. 14 was Oakley CL, a variety that has an extremely good resistance package for wheat streak mosaic.

"On a scale of 1 to 10, Oakley CL is a 2," he says.

K-State Extension wheat specialist Romulo Lollato says the exceptionally warm fall is probably responsible, because the resistance gene in Oakley is temperature-sensitive.

For farmers who lost a field to the virus, Lollato says that replanting is not really an option.

"The curl mites are probably still in the area, and rotating to another crop in the spring is a better idea," he says.

K-State wheat breeder Guorong Zhang at the Hays Research Station agrees that warm temperatures were probably to blame.

The resistance gene starts to break down in temperatures higher than 18 degrees C or about 65 degrees F, he says. "We had a lot of days in October and November that were warmer than that."

Zhang says that he did find a new race of wheat streak mosaic at the Hays station, but he thinks it is because Oakley CL has been planted continuously in the field, allowing the virus to overcome the resistance gene.

"I haven't actually seen the Lane County field, and it wasn't tested for race of virus, but I don't think there is much of it out there. I think a temperature breakdown is far more likely."

Seed treatments won't help, Ehmke says.

"I asked both KSU plant pathologist Erick DeWolf and entomologist Sarah Zukoff about whether treatments with insecticides would help with control of wheat streak mosaic through control of wheat curl mites," Ehmke says. "They agreed that there was no data to suggest that seed treatments will work:”

Ehmke says that controlling volunteer wheat is extremely important.

"Do yourself and the entire neighborhood a favor by getting that stuff killed," he says.

Finally, he suggests, if you want to plant early for grazing, forget wheat and go with rye or triticale.

"Both will produce a lot more forage than wheat, and you won't have to worry about wheat streak mosaic," he says.

Rebecca Davis, manager of the Risk Management Agency in Topeka, says wheat growers who have sustained losses to wheat streak mosaic should call their crop insurance agent and report the loss.

"It may or may not be covered," she says. "But if you have the crop insured, you need to call now and get the loss verified and those acres released, so you can plant another crop in the spring."

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