水稻恶苗病从苗期至抽穗期均可发生,一般有3个较明显的发病高峰期。在播种后15天左右出现第一个发病高峰,在水稻分蘖高峰期出现第二个发病高峰,在水稻孕穗期出现第三个发病高峰。在前两个高峰期发病较严重。苗期发病,病苗比健苗细高,叶片、叶鞘细长,叶色淡黄,根系发育不良,部分病苗在移栽前后不久死亡。病死植株表面产生分生孢子,能经风雨传播到健苗,从伤口侵入,造成多次再侵染。但这种再侵染能力比较弱,在田间侵染健康稻苗的 Rice Bakanae disease from seedling to heading stage can occur, there are generally three more obvious peak incidence. The first peak appeared at about 15 days after sowing, the second peak appeared at the peak of rice tillering, and the third peak appeared at the booting stage of rice. In the first two peak incidence more serious. Emergence of seedling disease, seedling thinner than the health seedlings, leaves, leaf sheath slender, leaf color yellow, poorly developed roots, some of the vaccine died shortly before and after transplanting. Conidiospores are produced on the surface of diseased plants and can spread to healthy seedlings through wind and rain, invading from wounds and causing multiple re-infection. However, this re-infection capacity is relatively weak, in the field infected with healthy rice seedlings