The Plant Pathology Journal ©The Korean Society of Plant Pathology A Forecast Model for the First Occurrence of Phytophthora Blight on Chili

An infection risk model for Phytophthora blight on chili pepper was developed to estimate the first date of di-sease occurrence in the field. The model consisted of three parts including estimation of zoosporangium formation, soil water content, and amount of active inoculum in soil. Daily weather data on air temperature, relative humidity and rainfall, and the soil texture data of local areas were used to estimate infection risk level that was quantified as the accumulated amount of active inoculum during the prior three days. Based on the analysis on 190 sets of weather and disease data, it was found that the threshold infection risk of 224 could be an appropriate criterion for determining the primary infection date. The 95 % confidence interval for the difference between the estimated date of primary infec-tion and the observed date of first disease occurrence was 8 ± 3 days. In the model validation tests, the observ-ed dates of first disease occurrence were within the 95% confidence intervals of the estimated dates in the five out of six cases. The sensitivity analyses suggested that the model was more responsive to temperature and soil texture than relative humidity, rainfall, and transplant-ing date. The infection risk model could be implement-ed in practice to control Phytophthora blight in chili pepper fields