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.摘要 本研究于圣保罗州雅莱什市开展两场葡萄试验，针对‘BRS Vitória’葡萄品种，评估不同施药频率下甲霜灵·代森锰锌（metalaxyl + mancozeb）对葡萄霜霉病（downy mildew）的防控效果，两场试验分别覆盖葡萄生产周期与枝条形成周期。试验采用随机区组设计，共设置5个处理组：1. 每周施药2次；2. 每周施药1次；3. 每14天施药1次；4. 每21天施药1次；5. 病原菌产孢后施药，每组设置4次重复，每个小区种植3株葡萄。通过病情进展曲线面积（Area Under the Disease Progress Curve, AUDPC）分析可知，两场试验中不同处理的防病效果均存在统计学显著差异（P=0.05），其中以每周2次施药的防控效率最优，其次为每周1次施药。相较于标准处理“每周2次施药”，“产孢后施药”处理的施药次数减少超90%，但该处理并未导致受害叶面积百分比出现显著升高，受害叶面积均低于3%，未对植株造成损害，亦未影响果穗品质与理化特性。