downy mildew

downy-mildew的词性：
n.（名词）

1. A disease of plants caused by fungi of the order Peronosporales and characterized by gray, velvety patches of spores on the lower surfaces of leaves.
霜霉病：霜霉科真菌引起的植物疾病，患此病的植物叶背面有一簇簇的灰色绒状胚芽