The pathogen overwinters mainly in soil with sclerotia, and also in host crops or weeds such as diseased rice stalks with hyphae and sclerotia. A large number of sclerotia that fell into the field at the time of rice harvest is the main source of initial infection in the coming year or next season. According to the survey, the number of sclerotia left in the field after rice harvest is 6,543,800+grains per mu in general diseased fields, 70/kloc-0,800 grains per mu in seriously ill fields, and a few of them are as high as 6,543,800+grains. The viability of sclerotia is extremely strong. According to the determination in Hunan, the survival rate of sclerotia overwintering on the soil surface is above 96%, and the survival rate of sclerotia overwintering 3-8 inches below the soil surface is about 88%. After ploughing and harrowing in spring, the overwintering sclerotia floated on the water surface, drifted with the water after transplanting and attached to the leaf sheath at the base of rice plants. With the increase of tillers and stems, the number of Sclerotinia sclerotiorum attached to rice stems also increased. Under suitable temperature and high humidity conditions; Sclerotinia sclerotiorum floating in water and sinking in water can germinate and grow hyphae, which extend on the leaf sheath and enter the inner side of the leaf sheath from the gap of the leaf sheath. First, adherent cells are formed and invade through stomata or directly through the epidermis. The incubation period ranges from 1-3 days to 3-5 days. Because sclerotia spreads with water, the influence of monsoon is mostly concentrated in the downwind angle of the field, and there are many sclerotia in the low-lying areas in the field, so these places are the easiest to find diseased plants.