The Severity Pattern of Powdery Mildew Under Rain-Sheltered Cultivation and the Screening of Highly Effective Bio-Based Pesticides

Frequent rainfall during the ripening season in Shaanxi’s grape-growing regions increases the incidence of downy mildew and black rot. In recent years, rain-shelter cultivation has reduced the incidence of these diseases; however, it has been associated with frequent powdery mildew outbreaks that severely compromise fruit quality and yield. To mitigate powdery mildew under rain-shelter conditions, we characterized disease dynamics and evaluated “bio-based” or “microbial-derived” pesticide control strategies. A large number of studies have shown that rain shelter cultivation can significantly change the microclimate. This study found that changes in microclimate affect the incidence pattern of powdery mildew, and there are significant differences in the resistance of different grape varieties to powdery mildew. A prediction model based on microclimate showed that 15-day accumulated growing degree days (GDD15; base 10 °C) before disease onset were positively correlated with the disease index (r = 0.860), whereas relative humidity was negatively correlated (r = −0.637); a multiple regression including both variables explained 81.4% of the variance. In biopesticide screening, blasticidin S and polyoxin inhibited spore germination by >95%. In-shelter efficacy varied among cultivars, and biopesticide effects on fruit quality were also cultivar dependent. For example, blasticidin S increased total phenol and anthocyanin contents in Cabernet Sauvignon but reduced phenolic accumulation in Chardonnay.