Symptoms occurred in the northeastern cotton area, the Yellow River valley, and the Yangtze River basin, along the river, and in the coastal cotton area. Cotton can be infected during the whole growing period, and the seedling and bud stage suffer heavy damage. The cotyledons and true leaves were infected with the diseased purplish-red borders and the middle gray-white round spots. The later lesions spread or merged into irregularly shaped lesions. In the center of the lesion, there are concentric ring patterns, on which small black particles are scattered, which is the conidia of the pathogen. Disease Department often broken and scattered, when the humidity is high, the young leaves appear immersed in water-like lesions, after the expansion of rapid like boiling water burned, wilting black, severe dry off, become light stalk and withered. The petiole and stem lesions were spotted in the center of light brown, surrounded by reddish purple, slightly sunken, and scattered with small black spots on the surface. Severe stems were dead or dead.
Boll lesions are similar to those on the stem. The middle color is darker and blacker. When the humidity is high, the lesion spreads rapidly, causing the cotton boll to become a frozen valve, and the bell cracks incompletely or does not crack.
The pathogenic Ascochyta gossypii Syd. called cotton shell bifida, belonging to the fungus Aspergillus Suberii. The conidia were initially buried under the epidermis of the cotton plant and were exposed on the epidermis after maturation. The spores are spherical, yellowish-brown, with a slightly projecting circular orifice at the top. The walls are relatively thin and fragile, with sizes ranging from 82.8 to 21075-189 (Î¼m), with many conidia endogenously. Conidia Oval, unit cells or twins, colorless, size 4.5-7.33.5-3.8 (Î¼m). The optimum temperature for the growth of the bacteria is 25Â°C.
Transmission Pathways and Pathogenic Conditions Germs are infected with mycelium or conidia inside or outside the cotton seed or with the diseased body in the soil or manure, and the cotton seedlings are infested in the spring and winter, and the conidia are produced in the diseased part to release the points. The spores are re-infested by wind and rain and locusts. The temperature during the seedling and budding period is stable above 20Â°C. Even the rainy days last for 3-4 days. The disease may occur or become popular within 3-5 days. Low temperatures and frequent rainfall on the production site often cause the disease to occur. Cotton aphid is a serious cotton field and the disease is heavy. The incidence of continuous cropping and management of extensive cotton fields is also heavy.
Control methods (1) Seed treatment methods See cotton black root rot. (2) Strengthen cultivation and management, implement rational crop rotation, intensive cultivation, seedling transplanting, rational fertilization, promote cotton strains, and improve disease resistance. (3) pest control and disease prevention. Prevention and cure of the disease combined with the treatment of sputum, it is predicted that the disease will be popular 1-3 days after the rain, and when the number of aphids is large, spray 1:1:200 times Bordeaux mixture or 70% mancozeb WP 500 times. , 50% benomyl WP 1500 times, and in the above liquid by adding 50% dimethoate EC or 80% dichlorvos EC 1000 times, both for cotton aphid.
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