Dr. Xianming Chen’s (ARS Plant Pathologist) most recent stripe rust update forecast was released last week – April 10, and little has changed from his March 6 update. Active stripe rust was observed in breeding nurseries at Central Ferry in Garfield County, and rust monitoring plots in Walla Walla and the OSU Research Center in Hermiston. The only stripe rust found in commercial fields was in the Horse Heaven Hills in Benton County, where incidence was 5%, and near Connell in Franklin County, where incidence was limited to one plant. No stripe rust was found in commercial fields in Adams, Columbia, Franklin, Garfield, Walla Walla, and Whitman counties in WA, and Umatilla County, OR. Consequently, that previous forecast for potential damage from stripe rust of 18% on susceptible checks holds. I want to emphasize again that Dr. Chen’s yield loss estimates are based on a highly susceptible variety that is not produced commercially and that susceptible winter wheat varieties like Eltan (rating 5), ORCF 102 (rating 6), and Xerpha (rating 7) have potential yield losses of 8 to 12%. Potential yield losses could occur assuming weather conditions remain favorable for rust development and no control measures are made.
For susceptible varieties rated 5 to 9 in the Seed Buyer’s Guide, fungicide application at herbicide timing is recommended, but already past in many areas. For more resistant varieties rated less than 5, and fields with susceptible varieties to which a fungicide may or may not have been applied, make sure to scout the field for stripe rust and apply a fungicide if 5% rust incidence or severity is found. Fungicide application should not be needed for resistant varieties rated 1 to 3.
Although this update brings good news, the temperatures over the past month have been on the cool side, which likely limited rust development. With temperatures predicted to rise over the coming week, it’s important to continue scouting fields for rust because this disease can increase rapidly under favorable conditions. It’s also important to remember that the fungicides used for stripe rust control have different growth stage restrictions and preharvest intervals for application. Make sure to read the label prior to application.
If you haven’t planted spring wheat yet, remember we always recommend planting the most resistant variety possible (rated 1 to 3) that performs well in your production area. You can use the Variety Selection tool to learn more about the resistant ratings of varieties.
Stay tuned for more rust updates as conditions change. In the meantime, you can find additional information on stripe rust, including photos showing rust percentage under the Foliar Fungal Diseases in the Disease Resources section of the WSU Wheat and Small Grains website.