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Poster: Epidemiology: Risk Assessment


A model for predicting onset of Stagonospora nodorum blotch in winter wheat based on pre-planting and weather factors
P. OJIAMBO (1), L. Mehra (1), C. Cowger (1) (1) North Carolina State University, U.S.A.

Stagonospora nodorum blotch (SNB), caused by Parastagonospora nodorum, is a serious disease of wheat. Its management relies mainly on fungicide application after flag leaf emergence. The disease can occur prior to flag leaf emergence but the impact of onset time on yield has not been determined. Using 390 disease cases collected across 11 counties in North Carolina from 2012 to 2014, the effect of SNB onset on yield was analyzed to identify a disease onset threshold. A model was then developed to predict the time of SNB onset using pre-planting factors and cumulative daily infection values (cDIV) starting 1 to 3 weeks prior to the disease onset threshold. Time of disease onset explained 32% of the variation in yield (P < 0.0001), and day of year (DOY) 102 was identified as the disease onset threshold. Below-average yield occurred in 87% of the disease cases when onset occurred before DOY 102, but only in 28% of those cases where onset occurred on or after DOY 102. A binary logistic regression model indicated that cDIV accumulated until two weeks prior to DOY 102 and wheat residue were significant (P < 0.0001) predictors of SNB onset. The model had a correct classification rate of 0.94, and specificity and sensitivity rates were ≥ 0.91. Internal model validation based on two cross-validation techniques was also high. The model could serve as a useful decision support tool for fungicide application for SNB management in wheat.