Detailed Explanation of the Harm and Control Methods of Clubroot in Chinese Cabbage

Clubroot of Chinese cabbage is a *soil-borne disease and pest* that causes relatively serious damage to cabbage. It often occurs from seedling emergence to the mature plant stage. Clubroot of Chinese cabbage can cause great harm to both the yield and quality of Chinese cabbage, so how can clubroot of Chinese cabbage be controlled?

I. Symptoms

In the early stage of the disease, the surface of the tumor is smooth; in the later stage, the surface becomes rough and uneven, with obvious cracking. The tumors on the main root can be as large as an egg, while their number decreases; the tumors on the lateral roots are very small, and the fibrous root tumors usually appear in strings, with as many as more than 20 in large cases.

II. Harm

The main damage is to the root system, causing tumors of varying sizes to appear on the main root or lateral roots, shaped like fingers, short rods, or spheres. The leaves gradually turn yellow from the bottom upward, and around noon on sunny days the plants wilt as if suffering from water shortage or nutrient deficiency.

III. Agricultural Control

1. It is forbidden to transport seedlings and vegetables and fruits from diseased fields in order to maintain disease-free fields. Strictly select disease-free land or newly reclaimed land for seedling raising, and pay attention to replacing diseased seedlings when planting and transplanting.

2. Improve alkalinized *soil*. It has been found that *soil* alkalinization is one of the key factors causing clubroot of Chinese cabbage. Using quicklime powder and silicon powder to adjust the *soil* pH has a good effect on controlling this disease. To adjust the *soil* pH well, apply 100 kg of quicklime powder per mu at the seedling stage before planting, then irrigate with moisture so that the pH value remains between 7-7.5. When the *soil* at the seedling stage is alkaline, the incidence of clubroot in the cabbage seedlings grown is significantly reduced. This is a simple and easy technical measure.

3. Use disease-resistant varieties. This is the best way to solve clubroot from the root. At present, the resistant varieties promoted on the market include Dafeng No. 2, Qingza No. 3, Improved Qingza No. 2, Chengyang Qing, Lüfeng No. 2, Lüxing 70, Jiaobai No. 10 and other varieties. All regions can adopt them according to local conditions.

4. Rotation and stubble change. In severely affected fields, rotation for more than three years should be carried out with non-cruciferous crops such as corn, wheat, rice and other grass-family crops, or with legumes such as soybean and kidney bean. Generally, in spring and summer, solanaceous vegetables, melon vegetables and leguminous vegetables can be planted; in autumn and winter, spinach, celtuce and onion, ginger and garlic vegetables and fruits can be planted instead.

5. Sun-dry the *soil* and use high-ridge planting. Transplanting should be chosen on sunny days; if there are 1-2 weeks of sunny days after transplanting, the disease incidence can be greatly alleviated; if it rains at transplanting or soon after transplanting, drench with 2% lime slurry to slow the disease. When harvesting the vegetables, it is best to pull them up with roots and bury the diseased nodules in pits 45-60 cm deep, apply lime, and then cover with *soil* to promote rotting of the vegetable roots and death of the pathogen. Pay attention to the combined application of nitrogen, phosphorus and potassium, and do not apply excessive or one-sided nitrogen fertilizer; attention should also be paid to field sanitation, and cruciferous weeds at the field edges should be removed promptly.

6. Use quicklime powder appropriately. When plowing, apply 75-100 kg of lime powder per mu to adjust the *soil* to slightly alkaline. Seven to ten days before transplanting, lime powder can be evenly applied to the *soil* surface and then formed into beds, or applied in holes at transplanting. After the disease occurs at the street edge, 2% aluminum chloride can be fully drenched on the bed surface, and then drenched once every seven days, which can greatly alleviate its harm. Or during the vigorous growth period of Chinese cabbage, irrigate the roots twice with 1% quicklime water.

IV. Chemical Control

1. Seed disinfection

For every 100 kg of seeds, use 500 ml of 25 g/L fludioxonil flowable seed coating agent, add 2 kg of water and mix well to carry out seed disinfection treatment. The disease prevention effect is good.

2. *Soil* or seedling disinfection

Before planting, the *soil* at the seedling stage must be disinfected. The method is: for wet *soil*, use 1:500 formalin solution and sprinkle 18 kg of liquid per sq m; for dry *soil*, use 1:100 formalin solution and sprinkle 36 kg of liquid per sq m, then cover with plastic film or straw matting. You can use 0.3 kg of 95% fenaminosulf wettable powder, mix with 30 kg of fine *soil* and apply it into the direct seeding furrow, then cover with *soil* and sow. Or before planting Chinese cabbage, evenly band-apply 70% quintozene or 50% thiophanate-methyl wettable powder on the bed surface, with a dosage of about 1.5 kg per mu, or when planting vegetables and fruits, irrigate with 500-fold dilution of 50% thiophanate-methyl wettable powder, irrigating 250 g of liquid per plant, and then irrigate once more after one month. Or before planting, after planting Chinese cabbage, irrigate the roots with a 2000-fold dilution, using 300 kg of liquid per mu, and then irrigate the roots once more after an interval of 7-10 days. In the planting field, irrigate the roots and spray the chemical when watering to settle the roots. Or before planting, soak the vegetable seedling roots in 800-fold dilution of 10% cyazofamid suspension for twenty minutes.

3. Control in diseased fields

In the early stage of the disease, when a small number of diseased plants are seen in the field, irrigate the roots with 500-fold dilution of 50% thiophanate-methyl wettable powder or 500-fold dilution of 50% triadimefon wettable powder, which has a good disease control effect. Use 0.5 kg of liquid per plant. Or use 1000-fold dilution of 20% oxolinic acid wettable powder to spray at the base of the diseased part, all of which have good control effects.

In summary, the above is the content on the control of clubroot in Chinese cabbage. Chinese cabbage growers and friends can refer to it for learning. Everyone should treat it early in the early stage of the disease; in the later stage it is very difficult to recover.