On March 1, Dr. Xianming Chen, ARS Plant Pathologist, released his most recent stripe rust forecast
for the coming season. During their February surveys 2 weeks ago, Dr. Chen’s team found active rust in commercial wheat fields in Lincoln County where rust was present in Fall 2019, but did not find rust in Adams, Benton, Douglas, Franklin, Grant, or Walla Walla Counties’ commercial fields. Rust was found in their experimental plot near Walla Walla. Dr. Christina Hagerty found active stripe rust in an experimental nursery near Pendleton in Umatilla County, Oregon during this same week.
Given the very mild weather that occurred from December through February, it was no surprise that the potential yield loss from stripe rust is predicted to be 48% on highly susceptible varieties with no fungicide application. This is an increase of 4% over the forecast made in January. Dr. Chen uses several models that incorporate weather data from November through February to arrive at this estimate. It’s important to keep in mind that this forecast is based on a highly susceptible variety that Dr. Chen uses as a long-term check with no fungicide application. Predictions of yield loss for moderately susceptible to susceptible commercially grown varieties is about 24% yield loss.
Given the mild winter and conditions favorable for severe stripe rust in 2020, it’s recommended that a fungicide is included at herbicide application for moderately susceptible to susceptible winter varieties, i.e. those with ratings of 5 to 9 in the Washington State Crop Improvement Seed Buyer’s Guide (link) and the Variety Selection tool on the Wheat & Small Grains website (link). Scout fields of varieties with ratings 1-4 and apply fungicide when 1-5% of plants have active rust (yellow-orange sporulation on leaves); it’s unlikely that varieties rated 1-2 will require fungicide application, but rust may develop on those rated 3-4.
For spring wheat, we recommend planting the most resistant variety possible, i.e. those with ratings less than 4.
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 page in the Disease Resources section of the WSU Wheat and Small Grains website.