Key points of pollution-free control of white rust of hollow cabbage

Symptoms: the disease spot grows on the back of the leaf, the leaf front appears yellowish to yellow spot, then gradually turns brown, the disease spot expands, and the back of the leaf produces white protuberant blister spots, which are nearly round or oval to irregular shape, and sometimes heal into larger blister spots. In the later stage, the blister spot ruptures and spreads out white impotent sporangia. When the leaves are seriously damaged, the disease spots are dense, the diseased leaves are deformed, and the leaves fall off. Main points of prevention and control: (1) choose disease-free seeds or mix seeds with 0.3% seed weight. (2) the disease is limited to infecting rosette vegetables. After 2-3 years of rotation, the disease control effect is good. (3) pay attention to the discharge of stains in the field and ventilation of sparse plants. (4) at the initial stage of the disease, 48% metalaxyl manganese zinc wettable powder, 40% methyl cream copper wettable powder, or 64% disinfectant alum wettable powder 600 times, 72.2% Procrylic water agent 800 times, once every 7-10 days, continuous prevention and treatment for 2-3 times.