Occurrence and control of brown class disease of lotus root

Brown class disease is the main disease of lotus root, which is widely distributed. It can occur in spring, summer and autumn. Generally, the diseased plant accounts for 30%-50%. In severe cases, the incidence rate can reach more than 80%, which significantly affects the yield and quality of lotus root. 1. Symptoms this disease mainly harms the leaves and petioles of lotus roots. The leaves have small brown-green spots at the beginning of the disease, and then expand into reddish brown to dark brown irregular to polygonal necrotic spots, with yellow halos on the periphery, the size of which is 2mm to 10mm, and the disease spots often have concentric lines, and in the later stage, the disease spots often merge with each other to form large patches, turn brown and dry. If the petiole is susceptible, it is easy to break and sag. When the air humidity is high, the surface of the disease spot will produce a gray-brown sparse mildew layer. two。 The pathogen overwintered with the diseased and residual tissue. When the temperature and humidity are suitable, conidia are produced and primary infection is formed. Conidia reinfection occurs after the onset of the disease. 3. ① agricultural control methods: combined with cutting stubble before winter, thoroughly clean up the diseased and residual old leaves, concentrate comminution and retting fertilizer, reduce the source of bacteria in the field, strengthen fertilizer and water management, increase the application of phosphorus, potassium and zinc fertilizer, timely and moderately drain the field, promote root growth, and enhance plant disease resistance. ② chemical control: at the initial stage of the disease, you can choose 50% dimethrin wettable powder 500x liquid or 40% Fuxing EC 5000 times liquid, or you can also use 70% methyl thiophanate wettable powder 600x liquid or 40% isoprazin wettable powder 600x liquid spray, spray once in 7 days and 15 days, 2 times in a row for 4 times.