Symptoms and control techniques of downy mildew in spinach

Downy mildew is a common disease of spinach, and the damage degree varies among years. Downy mildew of spinach is an obligate parasite, which only damages spinach. I. Symptoms Spinach downy mildew can infect leaves locally or systemically. When the leaves were infected locally, the affected parts were light green water-soaked circular spots at the beginning, and then expanded into irregular yellow spots, the edges were not obvious, and gray mold layers were produced on the back, and then they became purple-gray. Generally, the lower part of the plant first disease, gradually upward development, drought when the disease leaves yellow, humidity is easy to rot. When the system was infected, the diseased plant was atrophied, and a large number of purple-gray mold layers were produced on the back of the leaves. When it was serious, the diseased spots covered the whole leaves, and the leaves were withered. When the humidity was high, it caused rot. II. Route of transmission and conditions of disease The pathogen overwinters as hyphae on spinach and seeds or as ospores in diseased plants. In the following year, sporangia are produced and spread by air flow, rain, irrigation water, farm tools, insects and agricultural operations. The sporangia invade through stomata or epidermis and repeatedly infect under 7~16℃, rainy and humid conditions. The most suitable growth period of spinach downy mildew is when there are more than 5 leaves; the peak period of incidence is March to April in spring and September to December in autumn; generally, the incidence is light when there is less rain in spring, and the incidence is heavy when there is more rain in autumn. Perennial continuous cropping plot, adjacent to or continuous cropping with other frequently occurring downy mildew vegetables, low-lying, easy to accumulate water, too high sowing density, closed field, poor permeability, serious disease. III. Prevention and control methods 1, agricultural control seriously ill plots to implement 2~3 years rotation; strengthen cultivation management to achieve moderate density planting, reasonable irrigation; found infected plants removed in time; after harvest to remove residual branches and leaves. 2. Seed dressing can select 30% ruidumei or 25% metalaxyl wettable powder for seed dressing, and the dosage is 0.3~ 0.4% of seed weight. 3. Chemical control and spraying control in the early stage of disease, once every 7~10 days, continuous spraying 2~3 times. 58% metalaxyl manganese zinc wettable powder 500 times solution, 50% tuijunte wettable powder 500 times solution, 64% toxoalum wettable powder 500 times solution, etc. can be selected. If the disease occurs seriously, spray control can be carried out by spraying 800 times solution of 72% Kelu WP or 500~600 times solution of 50% Anke Mangzinc WP.