This study evaluates economic thresholds for a new web-based decision support system developed for precision fungicide management for potato production. We extend previous work (Zhang and Swinton, 2009), by developing an intra-seasonal dynamic economic optimization model. This model allows us to evaluate economic thresholds for disease control. The suggested model is applied to the problem of controlling potato late blight disease in 152 locations for 5 major potato producing states in the United States. The empirical results show that the economic thresholds improved disease suppression and farming profit relative to the previous critical thresholds while maintaining fungicide use efficiency.