Symptoms and identification: Rhizomatosis mainly harms the roots of plants. At the early stage of the disease, local swelling appears on the main roots and the first and second lateral roots, and the overground parts grow slowly. The outer leaves often wilt at noon and recover in the morning and evening. At the late stage of the disease, the root tumor grew up, with the maximum diameter of more than 10 cm, one or more of which varied, and symptoms such as yellowing leaves, dry leaf edges and dry heartburn occurred in the aboveground parts. After the Chinese cabbage plants were infected, the ability of heading was weakened, and the leaves were small and loose.
Control methods: ① control the source of seeds. Introduce seedlings from areas where clubroot does not occur, and strictly implement the quarantine system to avoid seed carrying bacteria. ② Improve the soil. When planting in areas where clubroot often occurs, the field should be sprinkled with hydrated lime 7 ~10 days before sowing or planting, and the dosage per mu should be 70 ~100 kg. Or at the early stage of the disease, irrigate the roots with 15% lime milk, with 0.3 ~ 0.5 kg emulsion per plant. ③ Strengthening cultivation management. Rotation with non-cruciferous vegetables for 4-5 years, and high ridge or high border cultivation. Increase the application of alkaline fertilizer, intensive cultivation, timely pull out diseased plants in the field and take them to non-water sources for destruction. ④ Chemical control. 75% pentachloronitrobenzene wettable powder can be used, with an amount of fine soil per mu1.5 ~ 3kg, and applied in furrow before sowing or planting. Or use 700 ~1000 times of 75% quintozene wettable powder, and pour it at the point before planting, with 250 ~ 500 grams of liquid medicine per mu. You can also use 50% thiophanate-methyl wettable powder1.5 ~ 3 kg, add a proper amount of fine soil, and apply it in furrow before sowing or planting; Or when planting, each plant is watered with 400 ml of benomyl solution (gram of active ingredient), and then watered every 1 month/time.