Downy mildew is one of the most destructive diseases affecting grape cultivation in Chongqing. It primarily affects the leaves, initially causing translucent, oil-like yellow spots that gradually expand into irregular yellow to brown lesions. These lesions vary in size depending on the grape variety and the severity of the infection. Under high humidity conditions, a white mold layer develops on the underside of the leaves, eventually leading to browning, leaf drying, and premature dropping. This disease typically peaks during the rainy season, from April to June each year.
To effectively manage downy mildew, a proactive approach is essential. Prevention should be the main strategy, combined with integrated control measures. Here are some effective practices:
Implement rainproof cultivation techniques to reduce moisture levels around the vines. Using greenhouses or plastic covers over the vine canopies during the growing season helps protect the grapes from rain, minimizing the spread of the disease and reducing its impact.
Adopt the "high, wide, thin, vertical" training system to improve air circulation within the vineyard. Planting at lower densities—such as more than 3 meters between rows and 1.5 meters between plants—helps maintain good ventilation. The recommended planting density is less than 111 plants per acre. The trellis system should ideally be a T-frame structure with high cordon points, usually above 1.3 meters, allowing for better sunlight exposure and limiting the growth of new shoots.
Improve vineyard management by digging deep drainage ditches to prevent waterlogging and keep the soil dry. Regular pruning, tying up vines, and weeding help maintain an open and well-ventilated environment. Apply organic fertilizers in September to November at a rate of over 2 tons per mu, along with micro-nutrients like boron, zinc, calcium, and adequate phosphorus and potassium. Bagging the fruit helps prevent pathogen infections. After winter pruning, remove and properly dispose of diseased leaves and branches by burying or burning them. Conduct thorough garden cleaning using a 5% sulfur solution before the vines begin to sprout.
Chemical control is also crucial. Early spraying is recommended, usually in mid to late May and early June, and again in late August to early September. Use products such as 66.8% propineb wettable powder (e.g., Moldgram) diluted 700–1000 times, 70% propineb wettable powder (Taisheng) diluted 400–600 times, 25% azoxystrobin suspension (Amisida) diluted 1000–2000 times, or 80% mancozeb wettable powder (Dasheng, Shan Desheng, etc.) diluted 600–800 times. These treatments have shown good results in controlling the disease. Avoid using powders in unsealed areas. After harvest, apply a Bordeaux mixture at 200 times dilution once for additional protection.
By combining cultural, mechanical, and chemical methods, grape growers can significantly reduce the occurrence and damage caused by downy mildew, ensuring healthier crops and higher yields.
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