防治病害的前提是正确的诊断,根据症状确定植物是否发病,及病害的类型,进而确定是哪一种病害,才能对症下药。但是,不同的病原物可以引起相似的症状,相同的病原物在不同的条件及不同的作物上又可以引起不同的症状,而且同一种病害在不同的发展时期可以出现几种不同的症状,正确识别有时较为困难。尤其在蔬菜上,特别是大棚等保护地蔬菜上,因为高温高湿的条件,非常利于各种病害的发生,往往多种病害混发,很多农民很难正确判断。但是,不同种类病害症状又具有一定规律性,防治方法也很相似。因此,根据症状判断出病害类型,即使不能明确判断是那一种病害,防治时也可以取得较好效果。这对专业知识较少而又缺乏仪器进 Prerequisite for the prevention and treatment of diseases is the correct diagnosis, according to the symptoms to determine the incidence of plants, and the type of disease, and then determine what kind of disease, can the right medicine. However, different pathogens can cause similar symptoms, the same pathogen in different conditions and different crops can cause different symptoms, and the same disease at different stages of development can show several different symptoms, the correct Identification is sometimes more difficult. Especially in vegetables, especially greenhouses and other protected vegetables, because of high temperature and humidity conditions, is very conducive to the occurrence of various diseases, often mixed with many diseases, many farmers is difficult to judge correctly. However, different types of disease symptoms have a certain regularity, prevention and control methods are also very similar. Therefore, according to the symptoms to determine the type of disease, even if it can not clearly determine the kind of disease, prevention and treatment can also get better results. This lack of expertise and lack of equipment into