1. Downy mildew is the main disease of lettuce. When it is severe, it can cause a large number of dead leaves and has a significant impact on yield. The disease is common at the beginning of winter season. The temperature difference between day and night in protected areas is large, and it is prone to condensation. During rainy season or when watering is too much, the water in the ground is heavy, the vegetation is too dense, the vegetation is too dense, the ventilation is poor, the humidity is high, and the incidence is heavy. The disease mainly damages the leaves. The lower leaves of the plant initially appeared pale yellow near-round lesions. Later expansion was limited by veins and was polygonal, and diseased leaves developed from the bottom up. When wet, white mold grows on the back of the leaves. In severe cases, it can also spread to the front of the leaves and also grows white mold. Later, the lesions expanded into yellow-brown and large-fallen spots, and finally the whole leaf died of dryness. 2. Control measures: When the seedlings are planted and colonized, the diseased plants are eliminated. Implement crop rotation, rational planting, diligent cultivator, more loose soil, strengthen air release and humidity, scientific watering, pay attention to drainage, and timely removal of diseased leaves. Before the onset of the disease or when the disease occurred, spray 2% antimycotic water agent 150 times, spray every 4 to 5 days, even spray 3 to 4 times. 30% or 45% chlorothalonil smoke agent can be used before the onset of lettuce in the protected area. 25% of downy mildew smoke can be used in the early stage of disease. 250 grams per acre is used. In the evening, 4 to 5 points are allocated to ignite smoking. After the closed room smoking prevention. 7 days smoked once, even smoked 4 to 5 times, can not be interrupted. Before the onset of disease, 5% chlorothalonil dust can be used. When the disease just happened, use 7% anti-mildew spirit dust agent. Use 1 kg per acre, spraying sooner or later. Once in 7 days, spray 4 to 5 times. 3, chemical control: before the onset, spray 75% chlorothalonil WP 600 times; early onset, spray 80% or 90% schisomide WP 500 to 600 times, or 70% MAP Wettable powder (or 58% metalaxyl MnZn wettable powder, 76% wet mildew wettable powder) 400 to 500 times, or 72% of Erysalactura WP (or 72.2% of Propomethrin) 600 to 800 times liquid. Choose sunny alternate spray, spray 7 days, spray 4 to 5 times. Pay attention to the bottom leaves and spray on the front and back of the leaves. Angiography Drape,Surgery Angiography Drape,Disposable Angiography Drape,Sterile Surgical Angiography Drape Xinxiang Huaxi Sanitary Materials Co., Ltd. , https://www.huaximedical.com