What is the cause of black spot of Chinese cabbage? How to prevent and cure?

Chinese cabbage is one of the common vegetables, and many farmers grow it. It is easy to appear black spots on leaves in the specific planting process, which is probably caused by black spot of Chinese cabbage. What is the cause of the disease? How to prevent and cure?

What is the cause of black spot of Chinese cabbage?

Alternaria brassica is a semi-known subphylum fungus, which is an anamorph fungus. The conidia pedicel olive brown, not often branched. Conidia solitary, spore with 5 × 12 diaphragms, several mediastinal membranes, gray olive brown, size 33 ~ 147 × 9 ~ 33 microns, beak with 1 × 6 diaphragms, size (27 ~ 111) microns × (4.9 ~ 7.4) microns, spore body to beak tapering. In addition, Alternaria brassicae and Alternaria radish can also be seen in some seasons or areas.

Most of the damage to cabbage starts from the outer leaves, and water-stained light brown round spots appear at the beginning of the disease, then turn into black-brown round spots, and when the humidity is high, there is black mildew on the disease spots. The disease spots on the stems and leaves are dark brown, fusiform, slightly sunken, ringed, and rot slightly in high humidity. When the disease is serious, the diseased leaves die or fall off.

Second, how to control the black spot of Chinese cabbage?

1. Seed treatment

The pathogen of black spot can be attached to the seeds of Chinese cabbage and directly infect the seedlings. Therefore, before sowing Chinese cabbage, the seeds can be mixed with 50% thiram wettable powder with 0.4% seed weight, or with 50% prohydantoin wettable powder with 0.2% seed weight and 0.3% seed weight.

2. Control the humidity in the field

In the disease-prone period, the humidity in the field is high and the disease is serious. The seedlings were fixed at the right time of ①. According to the variety characteristics and soil fertility of Chinese cabbage, appropriate plant spacing should be used to determine seedlings (not later than early September in Taiyuan area) in order to improve the ventilation condition in the field. ② was watered reasonably. In the disease-prone period, it is necessary to "look at the sky, look at the earth, look at the growth of Chinese cabbage" timely and appropriately according to the border watering, should avoid rainy days after watering. The stagnant water in the field should be discharged as soon as possible.

3. Foliar fertilization

If the plant is weak, in addition to strengthening the management of water and fertilizer, 0.2% potassium dihydrogen phosphate or 1% red (white) sugar can also be added to the spray solution to replenish the foliar nutrition.

4. Spraying as early as possible

After the pathogen of black spot invaded Chinese cabbage leaves, the disease spot could be formed after 3-5 days, and black mildew could be produced on the disease spot, and then invaded Chinese cabbage. Therefore, when disease spots appear on the lower leaves of Chinese cabbage, you can spray 75% chlorothalonil wettable powder 600x liquid, or 50% propofoin wettable powder 1500 times liquid, or 50% thiram wettable powder 500x liquid, or 64% poison alum wettable powder 500x liquid, spray once every 7 to 10 days, continuous spray for 5 times, 50kg per 667m2.

5. Points for attention

Land prone to disease: land with continuous stubble and adjacent stubble of cruciferous vegetables, land sown without seed treatment, land with early sowing, land with high plant density in the field, land with insufficient base fertilizer and topdressing fertilizer, land with weak plant growth, land irrigated by flood, prone to disease.

Vulnerable vegetables: in addition to Chinese cabbage, radish, cabbage, rape (Chinese cabbage or green cabbage), cauliflower (cauliflower), etc., vulnerable to the disease, control measures can refer to Chinese cabbage.