Dr. Xianming Chen’s (ARS Plant Pathologist) March 7, 2022 stripe rust update says that stripe rust will be in the moderate range for the 2022 growing season. His predicted yield loss of 20-40% is based on highly susceptible varieties that are not grown commercially; for commercial varieties grown in our region, potential yield loss ranges up to 24% for susceptible varieties.
It’s important to remember that Dr. Chen’s models are based on current and past weather conditions and don’t take into account how much stripe rust was present last fall. Recall that last year we had the least amount of stripe rust observed in at least 20 years as a result of the historic drought. In addition, dry fall conditions in 2021 were not conducive to early seeding and emergence, and stripe rust establishment. Consequently, the amount of overwintering stripe rust was also very low.
Dr. Chen’s team confirmed this when they did not find stripe rust in commercial fields in Adams, Douglas, Grant, Lincoln, or Whitman Counties in November 2021, and as of March 1, 2022, did not find stripe rust in Adams, Benton, Columbia, Franklin, Garfield, Walla Walla, or Whitman Counties. This tells us that stripe rust is getting a late start in 2022, which is good news.
Even though there is some good news, stripe rust can develop very quickly when conditions are favorable. Therefore, we recommend scouting fields for the presence of stripe rust and consider fungicide application when 1-5% of plants have active rust (yellow-orange sporulation on leaves). Given the current forecast, it’s unlikely that varieties with a stripe rust rating of 1-4 will require fungicide application, but rust may develop on those rated 5 and above in the Washington State Crop Improvement Seed Buyer’s Guide and Variety Selection Tool.
If you haven’t planted your 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.
I will provide more rust updates as weather conditions change and new predictions are released. 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.
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.