Predicting potato tuber yield loss due to early blight severity in the Midwestern United States

Although early blight is among the most damaging foliar diseases of potato, the information available on the disease-yield relationship is scarce. Twenty-three field trials were conducted from 2003 to 2016 across North Dakota and Minnesota potato growing regions to study the relationships among disease severity estimated from tuber initiation (TI) to early bulking (growth stage III to IV) and late bulking/tuber maturation (growth stage IV to V) and yield. The strength of the association and the functional relationships between crop and disease variables were assessed based on estimates of the Fisher's Z transformation of Pearson correlation r, the intercept (beta(0)) and slope(beta(1)) for each trial, which were combined and analyzed using meta-analytic models. At TI to early bulking stage, random-effect model estimated a slope of 0.20 mt/ha/%(-1) for an expected yield (intercept) of 61.88 mt/ha. Each unit increase in percent severity at this growth stage would result in a 32 percentage point (pp) yield reduction. During late bulking/tuber maturation crop growth stage, the random-coefficients beta(0) and beta(1) were 65.89 mt/ha and 0.13 mt/ha/%(-1), respectively. In relative terms, yield would be reduced by 19 pp. for each unitary percentage increase in early blight severity. Based on these meta-analysis results, growers are able to predict potential yield loss for each percentage increase of early blight severity at two growth stages, which can be useful for crop-loss assessments.