一、黄瓜霜霉病症状此病在黄瓜生长过程中发病较快，易流行、危害重。主要危害黄瓜叶片，苗期、成株期均可发病。子叶被害初呈褪绿色黄斑，早晨尤为明显，病斑逐渐扩大，受叶脉限制，呈多角形淡褐色或黄褐色斑块，湿度大时叶背面或叶面长出灰黑色霉层，后期病斑破裂或连片，致 First, the symptoms of cucumber downy mildew Cucumber disease in the growth of the disease faster, easy to epidemics, endanger heavy. The main hazard cucumber leaves, seedling stage, adult stage can be disease. The cotyledons were initially faded green macula, especially in the morning, the lesion was gradually enlarged, restricted by the veins, polygonal brown or yellowish brown patches, when the humidity is large, the leaves on the back or leaves grow black-gray mold layer, the late lesion Rupture or contiguous, caused