危害大葱的病害种类很多,其主要的有紫斑病、锈病、霜霉病和萎缩病等。各病害的识别与防治方法如下: 一、紫斑病该病是大葱、圆葱常见的一种危险性病害,分布普遍,危害严重。首先在叶片上发病,病斑为纺锤形,呈紫色并覆盖一层霉状物呈同心轮纹状排列。染病处变软易折断或茎部倒伏,严重影响产量与质量。在高温多湿的条件下发病快而重。病菌潜伏在病株残体组织内越冬。次年春天由风、雨传到大葱、圆葱等寄主叶片上,由气孔或伤口侵入寄 The types of diseases that endanger green onions are many, and their main diseases are purple spot, rust, downy mildew and wilt disease. Disease identification and prevention methods are as follows: First, purple spot disease is a common onions green onion, onion a dangerous disease, the distribution of common, serious harm. The first disease in the leaves, the lesion was spindle-shaped, purple and covered with a layer of mildew concentric concentric rims arranged. Soft spot easily broken or stem lodging, seriously affecting the yield and quality. In the hot and humid conditions faster and heavier. Bacteria lurk in diseased plants in the winter tissue. The following spring by the wind, rain spread to green onions, onion and other host leaves, invasion by stoma or wound