1. Disease: Downy mildew harms leaves, shoots, pedicels and flowers. In the initial period, irregular pale green markings appeared on the leaves, followed by tan and purple, and later gray-brown. The edges were darker and had no obvious boundaries with healthy tissues. Eventually causing blade distortion and malformation. When the weather is wet, a sparse layer of gray downy mildew can be seen on the lesions on the back of the leaves. The leaflets tend to turn yellow, some are purple-red, and the center is gray, similar to pesticide and chemical fertilizer burns. When the shoots and flowers were infected, the lesions were similar to the leaves, but the lesions on the shoots were slightly depressed. In severe cases, the leaves shrink and fall off and new shoots die.
2. Pathogens: Upland downy mildew is a type of fungus that is caused by the invasion of rose persecum (Peronospora sporsa Berk). The pathogens overwinter in the diseased tissue with oospore or mycelium. In the case of low temperature, high relative humidity, and water droplets on the surface of plants, the disease is prone to occur and spread. Poorly ventilated greenhouses, dense plants, high humidity, and excessive nitrogen fertilizers are serious diseases.
3. Incidence of disease: The pathogenic bacteria were infested with ovipositing spores during winter and conidia. The spore germination temperature was 1-25°C, and the optimum temperature was 18°C. The germination rate was lower than 21°C, and no germination was observed at temperatures above 26°C. 26 °C 24-hour spore death, spore transmission requires 100% air humidity, 10-25 °C temperature, spore germination requires the presence of water droplets, open cultivation occurs mostly in the rainy season, greenhouse occurs mainly in March-April and September-October, In the greenhouse. The seedbed is dense, poorly ventilated, humid, and heavily nitrogenous.
4. Control methods: Avoid high temperature and high humidity, reduce leaf moisturizing time, control air humidity, open more windows and change air; use 20000 times Daisen ammonium; 500 times mancozeb or manson manganese spray control, but the latter Easy to contaminate the blades.
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