大白菜生长中后期，常遭受软腐病、霜霉病、病毒病和黑斑病的危害，轻者产量降低，品质变劣，严重的会导致植株死亡。一、软腐病。发生在包心期。发病初期病株的外围叶片在中午萎蔫，早晚仍能恢复正常，以后萎蔫叶片不再恢复。严重时，病株枯黄皱缩，外叶脱落，结球小而外露， Chinese cabbage is often endangered by soft rot, downy mildew, virus disease and black spot in the middle and late stages of growth. The yield of light cabbage is reduced and the quality is worsened, leading to the death of plants. First, soft rot. Occurred in the inclusion phase. In the early stages of disease, the peripheral leaves of the diseased plants wilted at midday, returning to normal sooner or later. Afterwards, the wilting leaves no longer recover. In severe cases, the diseased plants withered yellow, outer leaves fall off, the knot is small and exposed,