1, onion black spot. In the damp and wet areas, the disease is easy to occur. At the beginning, brownish-oval, spind-shaped lesions are formed on the leaves, and the lesions are slightly depressed at the late stage. The lesions are dark purple, with concentric ring veins and powdery smoke on the upper part of the soot. The damaged part is softened and easily broken. 75% of chlorothalonil wettable powder can be used to prevent and treat this disease, or 50% of acetaminophen wettable powder can be used as 1500 times. 2, purple onion spot. In the hot and humid conditions, the disease is widespread. The lesions mostly occur in the leaves, spindle-shaped, slightly concave, concentric ring, purple and coated with mold. The affected area becomes soft and easy to fold, and the severe leaves die. To control the disease, use 40% carbendazim gel suspension 400 times, or 50% Daisen ammonium 600 times.