大白菜是我省城乡居民冬季食用的主要蔬菜品种，但近几年来，大白菜软腐病、霜霉病、病毒病三大病害严重制约着单位面积产量的提高。 大白菜霜霉病主要从外部叶片开始为害，初期叶正面产生淡绿色病班。然后病班逐渐扩大，色泽由淡绿变黄，因病斑扩展受叶脉限制而呈多角形，空气 Chinese cabbage is the main vegetable species consumed by urban and rural residents in winter in our province. However, in recent years, the three diseases of soft rot, downy mildew and virus disease of Chinese cabbage severely restrict the yield per unit area. Chinese cabbage downy mildew mainly from the external leaves of the victims, the initial positive leaves light green disease classes. Then gradually expand the sick class, the color from light green to yellow, due to lesion expansion by the limitations of the veins and was polygonal, air