病毒病、软腐病和霜霉病是为害大白菜的三大病害。这三种病害也为害萝卜、甘蓝、小白菜和莴苣等其它十字花科蔬菜。 一、发生与为害 1、病毒病 该病是三大病害中发生最早的一种。病毒在大白菜、萝卜、甘蓝等残株落叶和车前草、荠菜等杂草上越冬,由蚜虫传播为害,春秋两季均可发生,而以秋季为甚。该病的发生与气候条件关系密切,8—9月份高温干旱时,容易发病。天气多雨低 Virus disease, soft rot and downy mildew are the three major diseases that damage Chinese cabbage. These three diseases also harm other cruciferous vegetables such as radish, cabbage, cabbage and lettuce. First, the occurrence and damage 1, the virus disease The disease is the first of three diseases occurred. The virus in Chinese cabbage, radish, cabbage and other residual deciduous and plantain, shepherd’s purse and other weeds overwinter, spread by aphids, spring and autumn can occur, but in autumn is staggering. The incidence of the disease is closely related to climatic conditions, 8-September high temperature and drought, prone to disease. The weather is rainy and low