ISSUE 15 August 17, 2006
TIME TO CONTROL WHEAT STREAK MOSAIC VIRUS
Outbreaks of Wheat Streak Mosaic Virus (WSMV) occurred in several locations this year, and is some cases were severe. In all cases, the disease could be traced back to volunteer winter wheat that had not been controlled prior to planting of spring wheat. In some cases, the winter wheat volunteers were carry-overs from fields of two years ago.
WSMV can not be controlled once infection occurs. Control strategies are preventive strategies, and are aimed at preventing the wheat curl mite (the vector or transmitter of the virus) from having a living green bridge upon which to survive and transmit the virus. The green tissue infected at this time (August) may be spring wheat crops, volunteer winter wheat, green corn, or some grassy weeds. To break the cycle of wheat curl mite and virus survival, all winter wheat this fall should be planted under the following conditions:
1) Fields should be free of winter wheat, spring wheat and grass weeds prior to planting. This means burn-down herbicides should be applied at least two weeks prior to planting.
2) Winter wheat should be planted toward the end of the planting window. Earlier seeding greatly increases the risk of infection, as the wheat curl mites are more active during warmer temperatures.
3) Winter wheat should not be planted adjacent to green corn as corn can serve as a reservoir for the wheat curl mites.
4) Winter wheat volunteers, or spring wheat volunteers that have been known to survive under heavy snow, if left until next spring, must be controlled prior to planting spring grains next year.
For further information, a "Management Tips for WSMV" brochure is being printed this week and will be available through the NDSU Extension Service county offices or through the offices of the NDSU Extension Area Agronomists. In addition, an extension circular on WSMV, NDSU Extension Service publication PP-646, can be found at the following web site: http://www.ext.nodak.edu/extpubs/plantsci/smgrains/pp646.pdf.
FIELD SCOUTS FINISHING SUMMER SURVEY
NDSU IPM field scouts are finishing up their last surveys this week and will be heading back to school soon. I wish to thank Tom Arnold, Nathan Bird, Lance Block, Matthew Leiphon, Brandt Lemer, and Tom Gross for contributing to our knowledge of pest problems and distributions in our major crops in 2006. They did a good job in the heat of this summer.
The summer scouts surveyed 1147 wheat fields and 108 barley fields during the growing season, as well as looking for insects in canola, corn, soybean and sunflower. In wheat and barley, diseases were not severe this year over-all, with leaf spot diseases being most commonly observed.
Late in the season, the field scouts found a few (19) post-flowering fields with detectable scab symptoms, but field severities were very low, under 1% for all but one, which had 2% field severity. Only 3 of the surveyed barley fields showed any symptoms of head scab, and severities were below 1%. A complete report of wheat survey results will be published this fall in the ND Crop Production Guide, and survey results will be posted in maps on the NDSU IPM webpage, as well, at: http://www.ag.ndsu.nodak.edu/aginfo/ndipm/
Extension Plant Pathologist