Control of gray spot of Radix Isatidis

Symptoms of Radix Isatidis leaves on both sides of a round spot, 2 cm in diameter, slightly sunken, gray-white in the center, brown margin. In the later stage, the disease spot becomes thin and brittle, cracked or perforated, and brown mildew grows on it when it is wet, which is the conidiophores and conidia of pathogens. The old leaf gets sick first and spreads from the bottom up. In severe cases, multiple disease spots heal each other, and the leaves wither early.

The pathogen is Cercospora (Cercospora sp.), which belongs to the subphylum Cercospora. The regular bacteria overwintered with the diseased and residual tissue and became the primary source of infection in the following year, or spread in the new cultivation area with seeds. The daily average temperature of 23-25 ℃ was beneficial to the disease, and the disease spread rapidly. The peak period of the disease is from July to August. Control methods: ① rotation and cleaning the countryside, reducing the source of bacteria, strengthening field management, ploughing and weeding twice before closing ridges. ② opened ditches for drainage after rain to reduce the humidity in the field. In the early stage of ③, spray Bordeaux solution (1-100) to protect, or spray 65% Dysen zinc 600-800 times to prevent and cure. During the onset period, 36% carbendazim wettable powder or 40% chlorothalonil suspension, 50% methyl thiophanate wettable powder, 50% carbendazim wettable powder, 65% carbendazim wettable powder and 50% carbendazim wettable powder were sprayed once or twice every 10 days.