Probability of Disease Occurance for Potato Late Blight in Gorgan (Golestan Province, Iran) Based on Weather Conditions

Late blight, caused by Phytophthora infestans, is one of the most important diseases of potato in the world and Iran, especially in Golestan province. With regard to favorable weather conditions in the spring, high prevalence of the disease and hence extensive fungicides application can be observed in potato fields of Gorgan in Ordibehesht (mid April) of nearly every year. For prediction of the probability of the disease occurrence, recorded epidemics data in recent 10 years and weather data of the region were used. In order to modeling, 24 weather variables during six different periods (all the period of Farvardin (March-April), first 10 days, second 10 days, third 10 days, first 20 days and last 20 days of the month) were studied using logistic regression and discriminant analysis methods. After developing and comparing the statistical models, it was revealed that all the periods of Farvardin (March-April) is more suitable than other durations for modeling and four bivariate models were developed using the variables: total percipitation (P), number of rainy days (R), relative maximum temperature (Tax) and relative maximum RH (RHax) which showed total correctness value of 80-100% and coefficient of determination of 99.99%.