大葱紫斑病是大葱的最重要病害。除会为害葱外,还为害洋葱、蒜、韭菜。该病生长适温24~27℃。主要侵害叶片和花梗,偶可为害鳞茎。发病初期,病斑小,略凹陷,后逐渐变大,椭圆形或梭形,褐色到紫色。潮湿时病斑上生黑色霉层,并有同心轮纹,病部易折断。湿度大时布满黑褐色霉状物, Purple onion is the most important disease of green onions. In addition to harmful onions, but also harmful onions, garlic, leeks. The disease growth temperature 24 ~ 27 ℃. The main damage to leaves and pedicels, even harmful bulbs. Early onset, lesion is small, slightly depressed, then gradually larger, oval or fusiform, brown to purple. Lesions spotted on the black mold layer when wet, and concentric ring pattern, easy to break the disease department. Humidity is covered with dark brown moldy,