Forecasting Late Blight for Northwestern Washington Organic Potato Production

This study focused on adapting a disease forecasting system called WISDOM for use in managing late blight in organic specialty potato production systems of western Washington. Although disease forecasting models in crop production are generally known to reduce unnecessary fungicide sprays and fungicide application costs, none have been developed with late blight and organic potato production systems, or this region deliberately in mind. In this study, 13 years of historical environmental records and late blight observations at WSU-Mount Vernon NWREC were reviewed. WISDOM correctly predicted lesion onset 58 % (7 out of 12 years) and disease spread 92 % (11 out of 12 years) of the time. Therefore, we conclude that routine late blight fungicide seed treatment, a calendar foliar fungicide spray at crop green-row stage, and sanitation practices need to be integrated with the use of WISDOM in western Washington to insure success. Savings in fungicide costs and quantities will most likely be realized from eliminating unnecessary late blight sprays in a low disease pressure year rather than in an average disease pressure year.