Dr. Xianming Chen, ARS Plant Pathologist, released his most recent stripe rust forecast for the coming season on March 15 and it’s good news: his models predict stripe rust severity in the coming season will be at the low end of the normal range. Dr. Chen’s prediction of 20-44% yield loss doesn’t sound very low, but it’s important to remember that his models are based on a highly susceptible variety, much more susceptible than those grown in commercial fields. Translated into commercial varieties, average yield losses are expected to be about 5% if no control measures like foliar fungicides are implemented.
It’s also important to note that Dr. Chen’s team did not find any stripe rust in their survey of fields in Adams, Douglas, Grant, Lincoln, and Whitman counties in November 2020, and Columbia, Franklin, Garfield, and Walla Walla counties on March 9, 2021. This means that active stripe rust is not currently present and will be getting a later start in eastern Washington in 2021 than last year. The current predictions are a stark change from those in January that predicted 39% yield loss on highly susceptible varieties. This change in predictions is the result of cold weather in February.
As a result of the current forecast, Dr. Chen is not recommending preemptive early season fungicide application unless stripe rust is observed in a field. Stripe rust can develop very quickly when conditions are favorable and, as always, we recommend that you scout 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 1-2 will require fungicide application, but rust may develop on those rated 3-4 and higher in the Washington State Crop Improvement Seed Buyer’s Guide and the Variety Selection tool on the Wheat & Small Grains website.
For 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.
Stay tuned for more rust updates as weather conditions change. In the meantime, you can find additional information on stripe rust, including photos showing rust percentage under 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.