First Forecast of Stripe Rust for the Pacific Northwest in 2012
Based on the 2011 December temperatures, stripe rust yield loss on highly susceptible winter wheat cultivars is predicted to be 47%. The value is calculated using the formula Y (yield loss) = 84.3 – 0.323X, where X is the absolute value of the accumulated value of negative degree days based on daily maximum temperatures. The negative degree day value for a day equals the maximum temperature (oC) subtracted by 7 (oC). This is the first of a series of models we use to predict stripe rust damage on susceptible cultivars for the major wheat growing region in the Pacific Northwest. For more information about this formula and other formulas, you may refer to our recent publication (Sharma-Poudyal, D., and Chen, X. M. 2011. Models for predicting potential yield loss of wheat caused by stripe rust in the US Pacific Northwest. Phytopathology 101:544-554).
If we classify stripe rust yield losses into four categories, low (equal to or less than 20%), moderate (more than 20% but equal to or less than 40%), severe (more than 40% but equal to or less than 60%), and extremely severe (more than 60%), the predicted level of 47% for 2012 indicates a severe level, higher than normal (35%). For comparison, the 2010 stripe rust epidemic caused 60% yield loss and the 2011 caused more than 90% on highly susceptible winter wheat cultivars.
Please keep in mind that this prediction is based on the winter weather so far. If the weather conditions from now to June are close to normal, the prediction will be very close to the real disease situation. The other models using the weather data from the entire November to February give better predictions. Our next forecast will be in early March.