The downy mildew of lettuce was caused by the infection of flagellin, a subfungi fungus lettuce. It mainly harms crops such as lettuce and lettuce. First, the concise diagnosis of lettuce downy mildew mainly damage leaves. Occurs from the lower leaf of the plant near the ground, and initially produces faded green patches. The expanded lesion is yellowish. The veins are limited to a nearly circular or irregular shape. When the humidity is high in the field, a white mold layer is formed on the back of the diseased part of the leaf. Cysts and sporangia. Second, the occurrence of regular bacteria like low temperature and high humidity environment, the onset of the temperature range of 1 ~ 25 °C; the temperature of the onset of the environment is 15 ~ 20 °C, relative humidity of about 95%; the most suitable period for the susceptible period of adulthood. Onset of incubation period of 3 to 7 days. The main onset of downy mildew is from March to May and September to November. The annual incidence of heavy rainfall during the early spring or rainy season was heavy; the continuous cropping plots, low-lying areas, and poorly-drained plots were more severe; the crops planted densely, poorly ventilated and light-transmitting, and excessive nitrogen fertilizers were seriously affected. 1. Seed treatment: Before sowing, use 2.5% fludioxonil (Closure) to suspend the seed coating agent 3, and put the seeds in the refrigerator after coating, and soak at 3～5°C for about 48 hours to sow. Disease and increase germination rate. 2. Forklift rotation: The former is not suitable for green leafy vegetables, and promotes the rotation of crops for 2 to 3 years. 3, fine soil preparation: choose fertile soil, high dry terrain, drainage and irrigation will be two, water, fertility and conservation of the field cultivation. Apply sufficient organic fertilizer and apply sufficient base fertilizer. Minimize top-dressing or top-dressing, and top-dressing fertilizers should be used. Dissolve in water and combine with water for topdressing. 4. Proper and close planting: The spacing of the lettuce is 2525 cm, and the spacing of the lettuce leaves is 3030 cm. The light is sufficient for the growth of the plants, and the dense plants are easy to cause diseases. YT-S350 YT-S350 Shenzhen Sunshine Technology Co.,Ltd , https://www.shenzhenyatwin.com
Third, prevention and control measures