一、霜霉病:该病主要为害叶片,从幼苗至成株期都可发生,以生长中后期发生较重。植株的下部叶片先发病,叶面出现淡黄色近圆形病斑,逐渐扩大成不定形,或因受叶脉限制而呈多角形,病斑颜色转为黄褐色,潮湿时病斑背面长出稀疏的霜状霉层。许多病斑相连可使叶片枯干。 First, downy mildew: The disease is the main damage leaves, from seedlings to adult stage can occur to occur in the late growth heavier. Lower leaves of the plant first disease, the emergence of pale yellow nearly round lesion, and gradually expanded into indefinite, or due to the limitations of the veins and polygons, lesion color to brown, the back of the lesion grew thin when wet Creamy mildew layer. Many lesions can make the leaves withered.