霜霉病是大葱栽培中的主要病害之一,常导致商品性下降,产量降低甚至绝收,多雨年份发病尤为严重,须高度重视。一、症状大葱霜霉病有系统侵染和局部侵染两类,病株症状特点不同。系统侵染的病株是由土壤和种植材料传带的病菌侵染所形成的,表现出全身性的症状。局部侵染植株只在被侵染部位出现症状。大葱被病原菌系统侵染后,病株矮化,叶片扭 Downy mildew is one of the main diseases in onion cultivation, often resulting in decreased merchandises, reduced yields or even absolute harvest, especially in rainy years, which deserves great attention. First, the symptoms of green onychomycosis There are two types of systemic infection and local infection, symptoms and disease characteristics of different strains. Infected diseased plants are formed by infection of pathogens carried by soil and planting material and show systemic symptoms. Locally infected plants show symptoms only at the infected site. After the green onions infected by the pathogen system, diseased plants dwarfed, twisted leaves