How to prevent and control sclerotinia rot in napa cabbage? These methods you need to know

Napa cabbage is a major winter and spring vegetable in Northeast and North China. It can be eaten raw, stir-fried, salted or pickled in soy sauce; the outer leaves that fall off can be used as feed. Napa cabbage has many varieties, is rich in nutrients, and has certain medicinal value. It is widely grown, and in many parts of our country it is grown in. Napa cabbage is very prone to sclerotinia rot. What are the prevention and control methods for this disease?

1. Symptoms of sclerotinia rot in napa cabbage

When seedlings are affected, the young leaves first show clear veins and loss of green along the veins, then become mosaic and wrinkled. Irregular water-soaked lesions appear at the base of the stem, gradually becoming soft and rotten and producing white mold, causing damping-off.

When adult plants are affected, the disease usually starts at the base of the leaf midribs near the ground, then spreads to the entire leaf and even the whole head. Water-soaked light brown lesions appear on the affected leaves. Under humid conditions, they cause the head and stem base to rot, but without a foul odor. White cottony mycelium and black sclerotia grow on the surface of the diseased parts and on the roots. Small brown spots may appear on the petioles, and the area around the spots turns bright yellow. In dry conditions, the diseased parts dry up and become perforated, also bearing white mycelium and black sclerotia. As the disease develops, the leaves die, until the whole plant dies. In rapidly developing cases, the plant quickly wilts and dies, and eventually the stem epidermis of the diseased plant rots and peels away.

On seed-production plants, the stems are mostly affected. The stalk base is initially light brown and sunken, then turns white, the cortex decays, and the fibers separate into a tangled mass like loose hemp. The stem cavity becomes hollow and contains black sclerotia shaped like mouse droppings. In rapidly developing cases, the whole plant quickly wilts and dies. Affected plants often dry up and die before flowering, resulting in total loss of yield. Diseased seed-production plants during storage are especially severely affected; this is a devastating disease.

2. What are the prevention and control methods for sclerotinia rot in napa cabbage?

1. Eliminate sclerotia

Since sclerotia are the primary source of infection for this disease, eliminating sclerotia is the first measure for disease prevention.

① Crop rotation. Practicing alternate-year rotation with rice or grass-family crops can cause a large number of sclerotia in the soil to die off.

② Deep plowing. After harvesting cruciferous vegetables, carry out 1 deep plowing to bury the sclerotia in the soil layer below 2-3 cun, so that they cannot produce apothecia or the apothecia cannot emerge above the soil surface. Deep plowing is one of the important methods for reducing disease sources in dryland. In addition, cultivating during the apothecium formation period can destroy the production of apothecia or bury them in the soil, reducing the spread of ascospores.

③ Seed treatment. Seeds should be collected from disease-free, vigorous plants. If the seeds are mixed with sclerotia, they can be selected with 10% salt water or 20% ammonium sulfate water to remove the sclerotia floating on the water surface. The treated seeds must be repeatedly washed with clean water before sowing, so as not to affect the germination rate.

2. Remove yellow leaves

Thoroughly removing the yellow leaves at the lower part of the plants not only prevents the pathogen from spreading through aging yellow leaves, but also improves ventilation and light penetration and reduces humidity, which has a certain inhibitory effect on the disease. Removing yellow leaves can be done once each at the early flowering stage and the final flowering stage. The removed yellow leaves should be gathered and deeply buried.

3. Reasonable fertilization

Avoid over-applying nitrogen fertilizer, and increase the application of phosphorus and potassium fertilizers to improve the disease resistance of the plants.

4. Prevent flooding irrigation and drain promptly after rain. Use high-ridge cultivation in low-lying land.

5. Strengthen cellar management

Before and after seed plants are put into the cellar, strictly prevent them from freezing. When the cellar temperature rises and the humidity is too high, ventilate promptly to lower the temperature and humidity, and promptly turn the vegetables and remove diseased plants to strictly prevent the spread of disease in the cellar.

6. Chemical control

When seed-production plants enter the full flowering stage, if the rate of diseased leaf plants reaches 10% and the rate of diseased stem plants is about 1%, spraying should begin, then spray once about every 10 days, for a total of 2-3 sprays. The spray solution should be focused on the stem base of the plants, old leaves and the ground. Commonly used agents include 70% thiophanate-methyl wettable powder at 1000 times dilution; 50% thiophanate wettable powder at 500 times dilution; 50% carbendazim wettable powder at 500 times dilution; 50% dicloran wettable powder at 1000 times dilution; 5% dicloran powder at 2-2.5 kg per mu mixed with 15 kg of fine mud powder to make medicated soil, or 70% quintozene powder at 250 g per mu mixed with 15 kg of fine mud powder, evenly scattered on the ground between rows.