Cucumber blight is a soil-borne disease that commonly affects autumn cucumbers, especially in northern regions. The disease can lead to widespread plant death and reduce yields by approximately 30%, making it one of the most significant threats to cucumber production during the fall season.
This disease can occur throughout the growing season, particularly in summer and autumn. In the early seedling stage, the tender stems become waterlogged, soft, and eventually shrivel and die without falling over. Adult plants are also vulnerable, with infected stems showing signs of waterlogging. The upper parts of the plant may wilt, and large, round lesions appear on the leaves. Infected fruits become soft, sag, and develop white mold on their surface, emitting an unpleasant odor. This leads to deformed cucumbers and premature dropping of young fruits.
The bacteria responsible for the disease spread through irrigation water and field activities. High humidity and low-lying areas are especially prone to infection. Preventive measures are crucial to managing this disease effectively.
Crop rotation is one of the most effective strategies. It's recommended to avoid planting cucumbers in the same area for consecutive seasons or after other vegetables. Rotating with legumes or other compatible crops for 2–3 years can significantly reduce disease pressure. Using resistant cucumber varieties is also highly recommended. Seeds can be treated with warm water or grown into disease-free seedlings to enhance resistance. Grafted cucumbers using black-seed pumpkin rootstocks have proven very effective in preventing the disease.
Field management plays a key role in controlling the spread of blight. Raised beds should be used, with high and narrow ridges to improve air circulation. A typical ridge height is 15–20 cm, with a width of 30–40 cm, and spacing between ridges of 80–90 cm for wide ridges and 40–50 cm for narrow ones. Plant density should be around 3,800–4,000 plants per mu. Diseased plants and leaves should be removed promptly, and all dead material, roots, and weeds should be cleared after harvest to minimize infection sources.
Drip irrigation or under-membrane irrigation is preferred to prevent waterlogging. Flood irrigation should be avoided. Watering should be minimized at the first sign of disease to limit its spread. Mulching helps prevent bacterial attachment to stems, leaves, and fruits. Balanced use of nitrogen, phosphorus, and potassium fertilizers is important; excessive nitrogen should be avoided.
Once the disease appears, a 58% mancozeb wettable powder can be applied at a 500-fold dilution. Spraying should be done every 5–7 days, with three applications in total. The last spray should be completed at least 10 days before harvest to ensure safe harvesting.
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