As many of you know, the 2016 crop season was very favorable for stripe rust due to the mild winter and early spring with temperature and moisture conditions that were favorable for rust development. In some cases, this resulted in severe rust in fields planted to susceptible varieties and/or multiple fungicide applications to limit rust damage. Following harvest, early rains resulted in good seeding conditions through much of our area and the fall wheat crop emerged and was infected by stripe rust spores from late-maturing fields. Consequently, stripe rust was well-established in many winter wheat fields heading into winter of 2016-2017.
Overwintering stripe rust infections are nothing new; stripe rust potential in spring depends on how well the rust survives over winter, with mild winter temperatures resulting in greater survival than cold temperatures. Dr. Chen, USDA-ARS Research Plant Pathologist in Pullman, uses models based on average temperatures from November to February to predict rust severity and just released his first stripe rust forecast of the 2017 season last week. The current forecast is positive with stripe rust predicted to be in the low range, i.e. 6% yield loss on susceptible varieties. Although this is good news, it needs to be tempered by the fact that Dr. Chen’s models don’t account for snow cover, which insulates the rust from cold temperatures. Many areas of eastern Washington have had protective snow cover since the middle of December. Rust potential going forward depends on how long the snow cover persists and temperatures through February. As a result, we won’t really know how well the rust survived and the potential for rust until winter has broken.
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.