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Oral: Risk Assessment


Weather-based risk assessment models for common leaf spot and black seed disease of strawberry caused by Mycosphaerella fragariae
O. CARISSE (1) (1) Agriculture and AgriFood Canada, Canada

Common leaf spot of strawberry (Mycosphaerella fragariae) is a sporadic disease. On susceptible cultivars and under favorable weather conditions, M. fragariae causes black seed disease, reduced plant vigor, and reduced yield the following year. Logistic regression analysis was used to examine the relationship between weather and outbreaks of common leaf spot and black seed. Information collected at 100 location-years was used to develop the models. The response variables were fields with an average of more than 10 lesions per leaf at the beginning of flowering (10% flowering) or with black seed symptoms on more than 5% of the fruits at harvest. Nonparametric correlation and logistic regression analysis was used to identified combinations of temperature, relative humidity, and rainfall during the spring period (bud break to 10% flowering) as predictor variables. Based on model prediction accuracy, sensitivity, and specificity, only few models correctly classified fields (> 80% correct classifications). The best predictors were temperature and rain (frequency and duration). The best models were validated with an independent data set (n = 20) and prediction accuracy was similar than the accuracy for the original data sets. Considering that management actions such as fungicide applications are not needed every year and in every field, these models could be used to identify field at risk for common leaf spot and black seed diseases.