Dr. Xianming Chen’s (USDA-ARS Plant Pathologist) March 10, 2023, stripe rust forecast (PDF) says that stripe rust will be in the moderate range for the 2023 growing season. His predicted yield loss of 20-40% is based on weather conditions from November 2022 through March 2023. This forecast is greater than the 21% yield loss predicted in January. It’s important to remember that these forecasts are based on highly susceptible varieties that are not grown commercially; for commercial varieties grown in our region, potential yield loss ranges up to 27% for susceptible varieties, but much less for resistant varieties and susceptible varieties with fungicide application.
It’s also important to remember that Dr. Chen’s models don’t consider how much stripe rust was present last fall. Recall that we had relatively dry fall conditions in 2022 that were not conducive to early seedling emergence or stripe rust establishment. Consequently, the amount of overwintering stripe rust was below average.
Dr. Chen’s forecast also states that they did not find stripe rust in commercial fields in Adams, Douglas, Grant, Lincoln, or Whitman counties in November 2022; nor did they find any rust in commercial fields in Adams, Benton, Columbia, Franklin, Garfield, or Walla Walla counties as of March 9, 2023. As happened last year, it appears that stripe rust is getting a late start this year.
Although this is good news and we are not recommending prophylactic fungicide application, stripe rust can develop very quickly when conditions are favorable. Therefore, we recommend scouting fields for the presence of stripe rust, especially susceptible varieties, and consider fungicide application when 1-5% of plants have active rust (yellow-orange sporulation on leaves). Given the current forecast, winter and spring varieties with a stripe rust rating of 4 or less should not require fungicide application, but those rated 5 and above should be monitored and sprayed if rust develops.
If you haven’t planted spring wheat, we recommend planting the most resistant variety possible, i.e., those with stripe rust ratings less than 4. Check the WSU Variety Testing program results for plots grown near where you farm and select the most resistant variety that performs well. Variety ratings are available in the Washington State Crop Improvement Seed Buyer’s Guide and the WSU Variety Selection tool.
I will provide more rust updates as weather conditions change and new predictions are released. In the meantime, additional information about stripe rust, including photos showing rust percentage, and other Foliar Fungal Diseases on our website
For questions or comments, contact Tim Murray via email at tim.murray@wsu.edu, via phone at (509) 335-7515, or by following him on Twitter @WSUWheatDoc.