近年来,生菜霜霉病发生极为普遍,严重时叶片枯黄色,损失很大。先在下部或叶球外叶上发病,产生淡黄色、周缘不明显的病斑,扩展后受叶脉限制呈多角形。湿度大时,叶背面出现白色霜霉状霉层。后期病斑变为黄褐色,叶片上病斑相互连结成片,叶片枯死。一、病原菌。为莴苣盘梗霉,属鞭毛菌亚门真菌。除侵染 In recent years, the occurrence of lettuce downy mildew is extremely common, severe yellowish leaves, a great loss. First in the lower part of the outer leaf or leaf disease, resulting in pale yellow, peripheral lesions are not obvious, expanded by the limitations of the veins polygonal. When humidity is high, there is a white mold mildew on the back of the leaves. Late lesions become yellow-brown, leaf lesions on the link between each other into pieces, dead leaves. First, the pathogen. As lettuce Campanulaceae, is a flagellum subfamily fungus. In addition to infection