First, harm symptoms and identification. Chinese cabbage black spot is a systemic fungal disease. The main harm to the leaves, from the cabbage seedlings began to suffer, the Chinese cabbage into the rosette later suffered the most, thus affecting the late cabbage Chinese cabbage and its quality. In general, the middle and lower leaves of Chinese cabbage are the most affected, and serious lesions also occur on the top of the heart of the plants.
At the time of first onset, small black spots appear on the leaves, and then gradually expand to form dark brown concentric ring lentiguli, sometimes with perforation or rupture. When the humidity is too high, mildew is formed on both sides of the lesion, and the local or entire leaves of the diseased lobe appear yellow and scorch.
Second, the law of occurrence and epidemic conditions. The occurrence of melasma is related to the climatic conditions, the disease resistance of the varieties and the cultivation and management. The degree of mutual coordination plays a decisive role in the disease epidemic. High temperature and high humidity are conducive to the occurrence of diseases. Under conditions of suitable temperature of about 17°C, continuous rain or heavy fog, it is easy to become a disaster. Disease resistance of different varieties is different, the incidence of early sowing of the same species is heavy, and the incidence of late sowing is light. Where the flood irrigation, the lack of base fertilizer disease is heavier, and the seedlings that had been seeded before sowing have very little disease at seedling stage, and the damage during the latter part of the growing season is also light. According to field observations, black spot disease is the most serious disease in the outer leaves of Chinese cabbage, followed by the globules, and the lightest leaves; the older leaves of the feet are heavier. The order of incidence of the leaves is from the bottom up and from the outside to the inside.
Third, prevention and treatment methods. The main focus is on agricultural control, combined with selection of disease-resistant varieties, appropriate drug protection, and comprehensive prevention and control.
1. Implement crop rotation and do a good job in idyllic cleansing. Black spot disease not only harms cabbage, but also harms cruciferous vegetables extensively. The field of crucifer crops has been cultivated year after year. Black spot disease has been increasing year by year. Therefore, it should be planted with leguminous, melon, and eggplant crops, and the cabbage should be cleaned in a timely manner after harvest to reduce the source of field bacteria.
2. Strengthen field management
(1) and time Miao Dingmiao: To stay weak and strong, to stay small, and finally choose a strong seedling Dingmiao.
(2) Formulated fertilization: According to the growth needs of Chinese cabbage, and according to the formula for measuring soil, the output of 10,000 kilograms per acre shall be calculated. Before planting, 5000 kilograms of high quality farmyard manure and 50 kilograms of phosphate fertilizer shall be applied; during the seedling stage and the rosette stage. A total of 16 kg of pure nitrogen, 8 kg of phosphorus pentoxide, and 18 kg of potassium oxide were applied to the core and baling period.
(3) Reasonable irrigation: Small water ground irrigation at the seedling stage, appropriate water control during the rosette period, and large fertilizer and water during the filling period, but avoid bountiful flooding to keep the ground moist.
(4) Appropriate late sowing: The appropriate sowing time for Chinese cabbage in our county is about 1 week before Liqiu, and it should be sowed in a timely manner on the premise that it does not affect the later period of Chinese cabbage.
3, selection of disease-resistant varieties. At present, the disease-resistant and high-yield-storage variety in our county is Qingza Zhongfeng, followed by Fengkang 78, Fengkang 79, Fengkang 80 and so on.
4, seed treatment. To eradicate the germs of the seed itself, seed germination of 0.3%-0.4% 75% chlorothalonil wettable powder or 70% mancozeb wettable powder before sowing occurs. There is inhibition.
5, pharmaceutical control. When a central diseased plant emerges, it is immediately treated with medication, once in 7-10 days, for a total of 2-3 times, to control the occurrence of melasma. The agents used are: (1) 50% acetaminophen wettable powder 1000 times; (2) 75% chlorothalonil wettable powder 600 times; (3) 70% mancozeb WP wettable powder 600 times; (4) 64% antivirus WP 500 times liquid.