Cucumber downy mildew is the main disease of cucumber. The disease mainly damages the leaves of cucumber, pumpkin, sponge gourd and other melon vegetables. Generally, the old leaves of the lower part suffer damage first, and then spread upward and expand. In the early stage of disease, the leaves showed pale yellow spots on the leaves. After the lesions were expanded, the lesions were limited by veins to form square or polygonal yellow-brown lesions, and later the lesions healed into large spots. When the disease is severe, the entire leaf is yellow-brown and dry, eventually causing the plant to dry and die prematurely, shortening the harvest period, and seriously affecting the yield of cucumber. The loss can reach 20% to 60%. Therefore, prevention and control should be strengthened. First, the incidence of disease in the city year round from April to May and September to October is the peak period of the disease, autumn disease incidence is more important than spring planting melon, bacteria (sporangia) spread by air or rain, repeated infections, No significant wintering period. When a central disease strain occurs, the disease becomes rapidly prevalent at temperatures of 16 to 22°C, humidity of 85% or more, and rainy days and heavy dew conditions. Generally, the disease can be widespread after 15 to 20 days. However, under conditions of drought or temperatures above 30°C, the disease development is limited and the incidence is lighter. If the management is extensive, the fertilizer is insufficient or densely planted, water is not properly used, long-term accumulation of water, and melon gardens are shaded, it is easy to induce the disease. Second, the prevention and control methods 1. Selection of fine varieties: production should use anti-illness varieties, cultivate disease-free strong seedlings. 2. Strengthen management of melon gardens: Strengthen management of melon gardens, cultivating plants in order to facilitate ventilation and light transmission; achieve reasonable close planting, planting in high cabinets and deep trenches; scientific drainage and irrigation to prevent waterlogging; scientific fertilization, mainly organic fertilizers, organic Inorganic combination, nitrogen, phosphorus and potassium fertilizers; improve the growth environment of cucumber, do a good job of fitness cultivation, and improve the resistance of plants. 3. Elimination of the source: The diseased melon garden should be promptly cleared of diseased plants, to reduce the repeated infection of pathogens. 4. Pharmacy control: The focus of chemical control is to grasp the early stage of disease application. If the disease continues to develop, it should be sprayed 2 or 3 times every 10 days in order to effectively control the spread of the disease. Can use 58% of methosulfuron manganese 700 times or 25% Lei Duomi 800 ~ 1000 times and other fungicides spray control.
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