大白菜黑腐病、软腐病和霜霉病是现阶段大白菜的三大病害。由于这三种病害可连续或交替发生，从而可造成大白菜减产甚至绝收。 一般黑腐病苗期就可发生，病叶有“Ｖ”型病斑，叶脉变黑，组织变黄，病根部呈黄褐色，最后全叶变黄枯死；软腐病多在大白菜包心期开始发病，病菌从伤 Chinese cabbage black rot, soft rot and downy mildew are the three major diseases of Chinese cabbage at this stage. As these three kinds of diseases can occur continuously or alternately, which can cause Chinese cabbage to cut even without income. Common black rot can occur at the seedling stage, the diseased leaves have “V” type lesions, the veins become black, the tissues turn yellow, the diseased roots are yellowish-brown, and finally the whole leaves turn yellow; the soft rot is mostly in the heart of Chinese cabbage The onset of disease, bacteria from injury