Wheat Streak Mosaic Virus Surfaces in North Dakota

Plant pathologist says winter wheat planted before Sept 25 are infected; fields planted after Sept. 25 still appear healthy. Infected fields and spring wheat volunteers should be destroyed. Mites on infected plants will move if host crop is destroyed.

Published on: May 3, 2010
Wheat streak mosaic virus has been detected in early planted winter wheat in North Dakota.

Marcia McMullen, NDSU Extension plant pathologist, says there's a couple "areas of concern."

1) 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 in the warm November, and survived under the good snow cover that came in December. No symptoms of WSMV or the presence of wheat curl mites were found in examination of 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 survival of the wheat curl mite, 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.

2) Winter wheat. "Symptoms of WSMV have been observed in early planted winter wheat (Sept. 5) by Area Extension Specialist Dan Waldstein, in the North Central region of North Dakota. These fields were most likely infected last fall and the warm weather this spring has increased mite development and virus spread. 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. Spraying glyphosate on an already infected crop stimulates mites to seek a new, healthy crop. The risk of mite dispersal and virus spread from an infected field tends to follow an oval-shaped pattern according to prevailing winds. Research in Nebraska has suggested possible movement of up to one to two miles, depending on mite numbers in source fields. Distance of movement depends on several factors:  how severe the disease is in the source field and how big the mite population; the temperature (higher temperatures favor more rapid reproduction of mite and mite movement, and stresses crops); and 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.

For more information about WSMV and mite movement, see www.ianrpubs.unl.edu/epublic/live/ec1871/build/ec1871.pdf.

Source: NDSU Extension Communications