Symptoms: The main roots and stem bases of damaged plants are initially wetted with water, then turn black and rot, the lateral roots wither, and the cortex is easy to fall off. There is a dense layer of white snow on the surface of rotting roots, which is the mycelium of pathogenic bacteria and looks like black particles like mouse feces. This is the sclerotia of the pathogen. In the later stage, the water in the diseased stem evaporates, and the diseased part becomes dry and gloomy, and the epidermis breaks like hemp, and sometimes there are black particles like mouse excrement inside.
Epidemic law: the pathogen can survive or spread on the seeds, and the carrier rate of the seeds is 1.2% ~ 14.2%, which is mainly spread on the seed surface through the seed coat. In addition, bacteria overwintering in the soil with mycelium and chlamydospores can become the main source of infection in the next year. The incidence of this disease is related to soil moisture content. When the groundwater level is high or the water is accumulated in the field, the disease is the most serious when the water capacity in the field is higher than 92%, and the disease in the field with high terrain is lighter. Broad beans, wheat and rape are intensively cultivated in winter and the rotation is light. The difference between years is related to meteorological conditions. When sowing, the seedlings died seriously in rainy weather.
Control method: (1) Strengthen field management. Irrigation in time during drought; Timely drainage and drainage when it rains; Reasonable rotation, no partial application of nitrogen fertilizer; Reasonable close planting can make the field ventilated, improve plant disease resistance and reduce diseases. When sowing, cover the seeds with 50% carbendazim150g mixed fine soil per mu. (2) chemical control. At seedling stage, the roots were irrigated with 50% carbendazim 1000 times solution, or sprayed with 70% thiophanate 800 ~ 1500 times solution or 65% zineb wettable powder 600 times solution.