大葱干叶严重影响食用及经济价值。引起干叶的主要因素是病虫害。大葱疫病:病斑通常从中部开始,初期呈暗绿色水浸状,扩大后变成灰白色斑,致使叶片枯萎变干。潮湿时病部长出稀疏白色棉毛状霉,天气干燥时白霉消失,撕开表皮可见棉毛状白色菌丝体。该病适宜发生温度为25～30℃(阴雨天气),种 Onion dry leaves seriously affect the edible and economic value. The main cause of dry leaves is pests and diseases. Scallion disease: Lesions usually start from the middle of the initial dark green flooding, expanded to become grayish white spots, causing the leaves withered and dried. When wet, the disease grows sparsely white cottony mildew, white mold disappears when the weather is dry, and the cottony white mycelium can be seen by tearing the epidermis. The disease is suitable for the occurrence of temperature 25 ~ 30 ℃ (rainy weather), species