一、紫斑病主要危害大葱、洋葱,也危害大蒜、韭菜。危害叶片、花梗、鳞茎。初期病斑小,灰色至淡褐色,中央微紫色,有黑色分生孢子。病斑很快扩大为椭圆形纺锤形,凹陷,暗紫色,常形成同心轮纹。环境条件适宜时,病斑扩大到全叶,或绕花梗一周,叶片、花梗枯死或折断。严重影响鲜葱的产量、品质和种子成熟。在24℃～27℃温度下发病重,温暖多湿、连阴雨天、缺肥、植物生长衰弱、葱蓟马造成伤口时,发病严重。 First, purple spot the main hazards green onions, onions, but also endanger the garlic, leeks. Harm the leaves, pedicel, bulbs. Early lesion, gray to light brown, central purple, with black conidia. Lesions quickly expanded to an oval spindle, depression, dark purple, often forming concentric wheel pattern. Appropriate environmental conditions, lesions extended to the whole leaf, or around the pedicel a week, leaves, pedicel dead or broken. Seriously affect the fresh onion production, quality and seed maturity. Severe onset in the temperature of 24 ℃ ~ 27 ℃, warm and humid, even the rainy days, lack of fertilizer, plant growth and weakness, onion thrips caused by wounds, the incidence of serious.