Symptoms and Control Methods of Black Rot in Chinese Cabbage

Chinese cabbage is a very common vegetable, cultivated in all parts of our country, and there are many ways to eat it. Whether stir-fried plainly or pickled, it has its own unique flavor. Chinese cabbage has low requirements for the growing environment and is easy to manage. A common disease of Chinese cabbage is black rot, and once this disease occurs it will cause very serious damage to its quality. So what are the symptoms of black rot in Chinese cabbage? How to control it?

1. What are the symptoms of black rot in Chinese cabbage?

Black rot in Chinese cabbage occurs at every stage of growth. When seedlings and cotyledons are affected, the edges become water-soaked, the pith of the root turns black, and the plant quickly withers and dies. At the adult plant stage, lesions appear from the leaf edges and gradually spread inward, forming "V”-shaped dark brown lesions, with the surrounding area turning yellow and the boundary with healthy tissue being indistinct. The netted veins within the lesions turn brown or black. When the petiole is affected, the disease develops upward along the vascular bundles, which can form brown dry rot, with the leaf tilting to one side and half of the leaf turning yellow. In severely affected plants, most leaves wither and die or break off.

The pathogenic bacteria overwinter on seeds and on diseased plant residues in the field, and can also overwinter on seed-producing plants or overwintering vegetables. Infected seeds are the most important source of primary infection. In spring, the bacteria spread to leaves through rainwater, irrigation water, insects or farming operations, and invade through the water pores at the leaf margins, wounds on the leaves, and insect wounds. The most suitable conditions for disease development are a temperature of 20-30°C and a relative humidity above 90%; the most susceptible growth stages are from the rosette stage to the head-forming stage. Outbreaks often occur after storms. The disease is more severe in low-lying plots prone to waterlogging and plots with excessive irrigation, under continuous cropping, when undecomposed farmyard manure is applied, when planting is too dense, when dew remains on the leaves for a long time, when guttation occurs at the leaf margins, when management is extensive, when plants grow excessively or senesce prematurely, and when insect pests occur severely.

2. How to control black rot in Chinese cabbage?

1. Collect seeds from disease-free plants, and disinfect the seeds before sowing. Seeds can be soaked for 20 minutes in a 400-fold dilution of 45% amobam aqueous solution, then washed and air-dried before sowing; or soaked for 20 minutes in warm water at 50°C and then cooled with cold water; or treated with a seed dressing of 50% thiram wettable powder at 0.3% of the seed weight.

2. Carry out a 2-3 year rotation with non-cruciferous crops.

3. Sow at the proper time, water the seedlings at the proper time, carry out proper seedling hardening, promptly pull out diseased plants in the field and take them outside the field for deep burial, and spread lime on the diseased planting holes for disinfection.

4. Chemical control. At the early stage of the disease, promptly spray “Tianda 2116” at 800-fold dilution + “Tianda Nuosha” at 1000-fold dilution, 72% agricultural streptomycin soluble powder at 4000-fold dilution, Xinzhi streptomycin at 4000-fold dilution, 47% Kasumin wettable powder at 800-fold dilution, 70% dexon soluble powder at 1000-fold dilution, etc.

Therefore, growers should pay attention to choosing suitable varieties, suitable soil and correct management practices when growing Chinese cabbage, so as to effectively prevent the occurrence of black rot in Chinese cabbage.