Chinese cabbage and Chinese cabbage are prone to white cabbage (Chinese cabbage brown spot), which mainly occurs on the outer leaves. Often cause a certain loss and affect the commodity. In addition to harming cabbage, the disease is also harmful to rapeseed, mustard, cabbage, radish and so on.
First, the symptoms
Primary water-immersed round or nearly round small spots, enlarged to become polygonal or irregularly shaped light yellow-white spots, with a transverse diameter of 0.5 to 6 mm, light yellow-white, with slightly protruding brown bands on the edges (visible to light) The edge of the lesion is darker in color. When the lesions are many, browning of the whole leaves or large leaves may even cause the leaves to turn yellow and dry. When the humidity is high, the leaves are immersed in water and dried and then whitened and dried.
On Chinese cabbage, the disease starts from the outer leaves and gradually expands to the inside. The disease spreads rapidly, and the heart leaves can be reached within a few days. The production often turns into pieces of decay or dryness. Some are limited by veins and the lesions are slightly raised.
Second, the pathogen
Cercospora brassicicola P.henn., called the genus Aspergillus, is a fungus of the fungi. Conidiophores (color map 4) protrude from the underdeveloped sub-seat, each bundle of 4 to 18 or more, sapphire brown to brown, erect, rarely curved and branched, the upper and lower widths are more consistent, there are 3 ~ 6 clear diaphragms, size (105 ~ 188) micron Ã— (4.25 ~ 5.25) micron, very few knee joints. Conidia (color map 5) is colorless, needle-shaped or whip-shaped, base is truncated, top sub-sharp, with 10 to 11 diaphragms, size (85 to 250) microns Ã— (2.5 to 4) microns.
Third, the incidence of the disease and the route of transmission
The pathogens are covered with hyphae or conidiophores and the disease remains in the soil for wintering. The conidia can also adhere to the seeds and spread long distances as the seeds are transported. Whenever it appears on warm and rainy days, the diseased part produces a large number of conidia that flies with the wind to the cabbage leaves for initial infection and reinfection. The pathogen is at a temperature of 25-30 Â°C. Spores are required to be present in the germination of the conidia, especially in high humidity (relative humidity 98%~100%) or spore germination in water. Therefore, the warm and rainy weather or the low-humidity cultivation environment of the plantation is conducive to the onset.
Generally, the field adjacent to the early-ripening cabbage is susceptible to disease. In particular, excessive application of nitrogen fertilizer, high humidity in the field of clay or wetlands, shady or poorly drained plots. If the growing season encounters rainy weather or the humidity in the field is high and the temperature is high, the disease will expand rapidly and it will easily cause damage.
Fourth, comprehensive prevention
Agricultural control. Seed disinfection, soaking in warm water at 50 Â° C for 10 minutes, or using seed weight 0.3% more than 40%. Ketone wettable powder, or 45% oxazolone. Fumei double wettable powder is seeded and sown after 48 to 72 hours of sealing. Or seed dressing with 50% carbendazim wettable powder with a seed weight of 0.4%. And use resistant varieties.
Strengthen water and fertilizer management. Grasp the cultivation and disease prevention centered on fertilizer and water. Apply enough base fertilizer, early topdressing, nitrogen, phosphorus and potassium together, avoid partial application of nitrogen fertilizer, spray foliar nutrient in a timely manner, promote plant growth without strengthening, enhance resistance; timely watering, growth period Prevent dry water from inducing dry heartburn, and avoid flood irrigation to prevent soil from being too wet. It should also be combined with management to remove diseased leaves in a timely manner and concentrate on burning to reduce the source of bacteria.
Seriously and non-cruciferous vegetables are rotated for more than 2 years. Choose plots with flat terrain, fertile soil and well-drained plots. After the harvest, the soil is turned over and the diseased body is decomposed and decomposed. Sorghum or high ridge cultivation, suitable for late sowing, avoiding the hot and rainy season, controlling the water and fertilizer during the rose period.
Chemical control. Combined with prevention and treatment of other diseases, early spraying will prevent and control diseases. When the plant enters the filling phase, at the latest at the onset of the disease, spray 75% chlorothalonil WP + 70% Thiabendazole WP (1:1) 1000-1500 times, or 40% more. Ketone wettable powder 1000 times solution, 45% oxazolone. Fumei double wettable powder 1000 times liquid, 75% chlorothalonil wettable powder + 50% antibacterial special wettable powder (1:1) 800 ~ 1000 times liquid, with 45 ~ 60 kg per acre of pharmaceutical dosage, spray 2 ~3 times, once every 10 to 15 days, alternate medication.
In the early stage of severe disease, 70% thiophanate-methyl WP can be used, or 40% carbendazim. Sulfur suspension 800 times solution, 80% mancozeb wettable powder 800 times solution, 50% different bacteria. Fumei double wettable powder 1000 times liquid, 80% anthrax. Fumei WP 800 times solution, 50% ethyl mold. Carbendazim WP 1000 times solution, 40% synergistic metalaxyl WP 1000 times solution and other agents spray, once every 7 days, continuous control 2 to 3 times, each time 45 ~ 60 kg per mu.
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