By Xianming Chen
The current forecast is that highly susceptible winter wheat varieties would have 6 percent yield loss, in the low epidemic level range (0-20 percent yield loss). Based on this forecast, currently grown varieties would not have significant yield loss and early fungicide application at the time of herbicide application time for winter wheat would not be necessary. This forecast is based on only the temperatures of November and December 2016 and does not include snow cover into the models. If snow cover has been and will be about 3 inches or higher during the periods of temperatures below 14 degrees F, the stripe rust fungus in wheat leaves will likely survive the winter. If so, the stripe rust level will be higher than the forecasted value. Therefore, a more accurate forecast will depend upon whether or not and to what degree the pathogen will survive throughout the winter. In early March, we will make another forecast based on the weather conditions of the entire winter season, which is generally more accurate than the early forecast. We will also check in early March if rust survived the winter.
On Nov. 8, 2016, we were checking winter wheat fields in Whitman, Lincoln, Adams, Grant, Douglas and Benton counties in Eastern Washington. High rust incidences were found in many fields. After that, there were several reports of stripe rust in Eastern Washington, northeastern Oregon and southern Idaho. The stripe rust infection in the fall was the most severe and widespread in the eastern Pacific Northwest (PNW). The cold weather conditions (below 14 degrees F) should have killed some rust, but snow cover could protect the rust fungus in wheat leaves.