大葱在夏末秋初的生长期间,最容易发生紫斑病、霜霉病、锈病,同时还易发生潜叶蝇、葱蓟马、葱蛆3种害虫。下面将其为害症状和防治方法介绍如下: 一、病害的症状和防治方法 1.紫斑病此病在高温潮湿的条件下发生普遍,从出苗到收获连续发生。病斑多为谈褐色,形状为纺锤形,稍凹陷,后变为紫色并有霉状 Scallions, purple molds, downy mildew are most likely to occur during the growth of late spring and early autumn in early spring, and three pests such as leaf miner, onion thrips and onion maggot are also prone to occur. The following symptoms and prevention methods are described below: First, the symptoms of disease and prevention and control methods 1. Purple spot disease occurs in hot and humid conditions in general, from emergence to harvest continuous occurrence. Mostly brown spots on the talk, the shape of spindle-shaped, slightly depressed, then become purple and moldy