Development of Weather- and Airborne Inoculum-Based Models to Describe Disease Severity of Wheat Powdery Mildew.

Disease severity of wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, was recorded weekly in fungicide-free field plots for three successive seasons from 2009 to 2012 in Langfang City, Hebei Province, China. Airborne conidia of B. graminis f. sp. tritici were trapped using a volumetric spore sampler, and meteorological data were collected using an automatic weather station. Cumulative logit models were used to relate the development of wheat powdery mildew to weather variables and airborne conidia density. Density of airborne conidia was the most important variate; further addition of weather variables, although statistically significant, increased model performance only slightly. A model based on variables derived from temperature and humidity had a generalized R of 72.4%. Although there were significant differences in model parameters among seasons, fine adjustment did not increase model performance significantly.