This disease can be caused by pythium, Fusarium, Phytophthora and other pathogens. Bacteria overwinter in the soil or on the sick and disabled, becoming the main source of primary infection in the following year. Bacteria invade from roots or roots and spread through rain or irrigation water. Fields with low terrain, poor drainage, water accumulation in the field, continuous cropping, dripping water and leaking water in the shed, and injured plant roots are seriously ill. Rainy years in spring and rainy years in plum rains are serious.