Wheat streak mosaic virus (WSMV) has been detected in early planted winter wheat and concern has arisen about this disease in volunteer spring wheat.

There are several areas of concern, according to Marcia McMullen, North Dakota State University Extension Service plant pathologist, and Joel Ransom, NDSU Extension agronomist.

One issue is spring wheat volunteers. Considerable areas of spring wheat volunteers that survived the winter are being observed across the state.

“Though very unusual, it appears that spring wheat germinated in the fall, mostly during the warm November, and survived under the good snow cover that came in December,” Ransom says.

No symptoms of WSMV or the presence of wheat curl mites were found while examining spring wheat volunteers from Cass, Richland and central North Dakota counties. Most spring wheat volunteers may have germinated late enough to have broken the green bridge necessary for the survival of the wheat curl mite, which is the transmitter of WSMV. Although no evidence of disease has been found in these volunteers, they should be destroyed prior to planting another wheat crop because of herbicide timing and harvest concerns.

Symptoms of WSMV in winter wheat have been observed by Dan Waldstein, NDSU Extension area specialist at the North Central Research Extension Center in Minot, in early planted winter wheat (Sept. 5).

“These fields probably were infected last fall and the warm weather this spring has increased mite development and virus spread,” McMullen says. “Later planted winter wheat (Sept. 25) in the same area appears symptomless and healthy at this time.”

Growers with symptomatic winter wheat still have time to destroy these crops and plant another crop.

Can mites from these infected crops move into adjacent winter wheat or spring wheat crops, even after herbicide treatment to destroy infected plants?

“Potentially, yes,” Ransom says. “Spraying glyphosate on an infected crop stimulates mites to seek a new, healthy crop.”

The risk of mite dispersal and the virus spreading from an infected field tends to follow an oval-shaped pattern according to the prevailing winds. Research in Nebraska suggests possible movement of up to one to two miles, depending on mite numbers in source fields.

The distance of the mite movement depends on several factors:

• How severe the disease is in the source field
• How big the mite population is
• The temperature (higher temperatures favor more rapid reproduction of mite and mite movement, and stresses crops)
• Rainfall (lack of rain increases mite movement and puts more stress on remaining crops)

“The best scenario for adjacent crops would be cooler temperatures and good rainfall,” McMullen says.

Information about this disease and mite movement is available in a University of Nebraska publication, “Managing Wheat Streak Mosaic,” which can be found at http://www.ianrpubs.unl.edu/epublic/live/ec1871/build/ec1871.pdf.

NDSU Agriculture Communication