The 2017 crop season was a mixed bag for stripe rust; although stripe rust was present, it was not nearly as severe as it has been over the past few years due to a combination of resistant varieties, timely fungicide applications, and less favorable weather conditions. Based on Dr. Xianming Chen’s late fall 2017 observations and his January 2018 forecast (pdf), just released last week, it appears that stripe rust will not be a major factor this season, at least not in the early season. Dr. Chen, USDA-ARS Research Plant Pathologist in Pullman, checked winter wheat fields in Adams, Douglas, Grant, Lincoln, and Whitman Counties in early November and did not find any stripe rust. This is substantially different than the same time in 2016 when stripe rust was well-established in many area fields. As he notes, the absence of rust in eastern WA winter wheat fields during fall is normal, since most overwintering occurs in areas with more mild winter temperatures. Survival of stripe rust overwinter depends on temperatures during December, January, and February. Based on rust survival models using November and December temperatures, stripe rust for the 2018 season is predicted to be in the low end of the epidemic range with 0 to 20% yield loss. It’s important to remember that the models are based on highly susceptible varieties that are not adapted to eastern WA conditions. Translating the model prediction onto varieties that are actually grown in the region indicates that yield loss would be less than 3%.
Although this is good news, we need to remember that Dr. Chen’s models don’t account for snow cover, and that rust potential going forward depends on snow cover duration and temperatures through the remainder of January and February. In contrast to the winter of 2016-2017, most of the wheat-producing area of eastern WA has had little or no snow cover, which is good for reducing stripe rust, but not good for winter wheat survival if we experience very cold temperatures. The most accurate prediction will come in March when we have a much better idea of winter survival of stripe rust.
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.