It's a blight, and it's important to prevent it. In addition to selecting plots with good drainage, low water level and loose soil, we should also choose disease-free seedlings for cultivation, preferably test-tube seedlings; In addition, the soil should be washed, and 5 kilograms of bleaching powder should be mixed with 10 ~ 15 kilograms of sand per mu, which should be evenly scattered in the garden before it rains, and washed with rainwater for three times, namely 1 time before planting, 1 time after planting and 1 time before budding. If a diseased plant is found, it should be pulled out immediately and the soil should be disinfected with lime to prevent the spread of the disease.