1.看病症发生发展的过程蔬菜病害具有传染性。因此,病害的发生一般具有明显的发病中心,然后迅速向四周扩散,通常成片发生,若不及时防治,可给蔬菜生长造成很大危害。而缺素症一般无发病中心,以散发为多,若不采取补救措施,会严重影响产量和品质。 1. To see the development of the disease process of vegetable diseases contagious. Therefore, the occurrence of diseases generally have a clear center of disease, and then quickly spread to the surrounding, usually into a film, if not timely control, can cause great harm to the growth of vegetables. In general, there are no disease-causing centers for the lack of disease, so as to distribute as much as possible. If no remedial measures are taken, it will seriously affect the yield and quality.