山楂白粉病是山楂的重要病害,幼苗及嫩梢被害时,顶端叶片及幼苗嫩茎出现黄色及灰白色斑块,以后叶片两面均可生出白粉,厚者呈绒毯状。叶片发病严重时病斑发展至全叶,渐萎卷缩,变褐枯死。苗茎顶端被害时,展叶迟缓,叶片扭曲纵卷,6月中下旬后病斑变为淡紫色或褐色,并在顶梢及叶腋间生出很多密集的小黑点。山楂树在春季发芽时,病芽萌发较晚,新梢嫩叶被覆白 Hawthorn powdery mildew is an important disease of hawthorn. When young seedlings and young shoots are killed, yellow and gray patches appear on the top leaves and young shoots. Afterwards, both sides of the leaves produce white flour, while the thick ones are napped. The incidence of severe leaf lesions to the development of the whole leaf, wilting curl, browning dead. When the top of the seedling stems are killed, the leaves are slowed, the leaves are twisted and curled, and the lesion becomes lilac or brown after mid-to-late June, and lots of dense black spots are formed on the tops and leaf axils. Hawthorn germination in the spring, the bud germination late buds of young shoots were white