Use of Simulation Models to Develop a Low-Risk Strategy to Suppress Early and Late Blight in Potato Foliage

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Abstract
Simulation models describing potato early blight development, potato late blight development, and chlorothalonil dynamics were used in analyzing the effect of fungicide applications on disease epidemics. The early blight model previously had received less validation than the other models and therefore was validated by independent sets of data (12 epidemics that had developed in susceptible and moderately resistant cultivars over 2 yr). The early blight model and the previously validated late blight model were used to evaluate the contributin of each fungicide application in a weekly application schedule (common grower practice) relative to overall foliar disease suppression. For early blight, applications beginning at 6-7 wk after planting were the first to make a positive contribution to disease suppression. This timing was consistent regardless of the inoculation date or the susceptibility group of the cultivar. For potato late blight, sprays applied at or just after the date of inoculation were important for suppressing the disease. The date at which sprays can be safety terminated (date of the last application) was similar for both diseases: approximately 3 wk before vine kill. Based on these results, we developed a fungicide use strategy with the goal of reducing the number of sprays while maintaining a low risk of severe disease causd by either pathogen. Our results indicated that using the proposed strategy may save two to four sprays in the northeastern United States without increasing risks from inadequate.