Frequency of fungicide application for controlling downy mildew in seedless grape plant ‘BRS Vitória’

Abstract Different application frequencies of metalaxyl + mancozeb were evaluated to control downy mildew in vine plants ‘BRS Vitória’ in two experiments conducted in Jales, São Paulo, one in the production cycle and another in branches formation cycle. In experimental design of randomized blocks, five treatments were compared (1- two weekly applications; 2- one weekly application; 3- one application every 14 days; 4- one application every 21 days; 5- applications after sporulation) with four replications, each plot with three plants. According to the analysis of the area under the disease progress curve (AUDPC), in both experiments, there were statistically significant differences between the disease control levels provided by the different treatments (P = 0.05), being the control more efficient when there were two weekly sprayings with metalaxyl + mancozeb, followed by one weekly spraying. Regarding the number of sprayings of the treatment “spraying after sporulation” there was a reduction of over 90% when compared to standard treatment, “two weekly sprayings.” This reduction, however, did not result in a significant increase in the percentage of affected leaf area, which was less than 3%, causing no damage to the plant and not interfering with the quality and the physicochemical characteristics of clusters.