甘蓝、白菜、萝卜霜霉病危害症状霜霉病为十字花科蔬菜常发性病害,春秋两季多发。苗期开始发病,下部叶片初生退绿斑,逐渐变为淡黄色,中央略带黄褐色稍凹陷斑,受叶脉限制呈多角形,湿度大时叶背或叶面生稀疏白色霉状物。病斑连片后叶片呈黄褐色干枯,病重时,病斑成片,叶片枯萎。农业防治从无病株采种;苗床换土,培育无病苗;实行与非十字花科蔬菜2年以上的轮作。 Cabbage, cabbage, radish downy mildew Hazard symptoms Downy mildew is cruciferous vegetables often disease, multiple seasons spring and autumn. Seedling begins to develop. The lower leaves begin to regain green spots and become yellowish gradually. The center is slightly yellowish brown and slightly depressed. The leaves are polygonal under the restriction of the veins. When the humidity is high, the sparse white mildew is formed on the leaves. After the lesion contiguous leaves were brown dry, ill, lesions into pieces, withered leaves. Agricultural prevention and control of seedless plants from planting; seedbed soil replacement, nurturing disease-free seedlings; implementation and non-cruciferous vegetables more than 2 years of rotation.