俗谚说 :“头伏萝卜、二伏菜。”近年来 ,农民为了让白菜提早上市 ,种菜时间提早到头伏 ,由于昼夜温差大、管理不当等原因 ,霜霉病越发严重 ,轻者减产２０ %～５０ %,重者达到绝收的程度。病状特点 :病斑在叶片中央受叶脉限制呈多角形 ,由黄白色渐变黄褐色 ,叶背面可见霜状霉层 As the saying goes: “the first carrot, two-volts.” In recent years, farmers in order to make cabbage early market, planting time to head and volts, due to large temperature difference between day and night, mismanagement and other reasons, downy mildew more serious, light production 20 % ~ 50%, heavy to achieve the absolute level. Pathological features: lesion in the center of the leaves by the veins were polygonal polygonal yellowish white gradient yellow-brown,