On March 8, Dr. Xianming Chen, ARS Plant Pathologist, released his most recent forecast (pdf) for stripe rust severity in the coming season. Given the very mild weather that occurred throughout January and the first part of February, it was no surprise that the potential damage from stripe rust increased to almost 18% over the 6% that was forecast in January. Dr. Chen used six models that incorporate weather data from November through February to arrive at his most recent estimate. The 18% damage forecast this month is an average of the range of values from 13.8% to 23.4%, which puts this year in the upper end of a low severity epidemic.
In contrast to the 2017 season, stripe rust was not found in any commercial winter wheat fields surveyed in Adams, Columbia, Franklin, Lincoln, Walla Walla, or Whitman counties during this past week (March 7). Active stripe rust was observed on the susceptible check variety in an experimental plot in Walla Walla, but this is typical for this location and time of year.
It’s important to remember that Dr. Chen’s yield loss estimates are based on a highly susceptible variety and he notes that the most susceptible winter wheat varieties like Eltan (rating 5), ORCF 102 (rating 6), and Xerpha (rating 7) could have yield losses of 8 to 12%. It’s also important to remember that these are potential yield losses assuming weather conditions remain favorable for rust development and no control measures are made. In this case, Dr. Chen recommends applying a fungicide with herbicide application if the variety is rated 5 to 9 in the Seed Buyer’s Guide and stripe rust is present in the field. For more resistant varieties rated 4, make sure to scout the field for stripe and apply a fungicide if rust is found. Fungicide application is not recommended for resistant varieties rated 1 to 3.
With spring wheat planting season approaching, we always recommend planting the most resistant variety possible that performs well in your production area. You can use the Variety Selection tool on this website to learn more about the resistance 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.