Stem blight of cotton

The symptoms were more serious in the northeast cotton area, the Yellow River basin, the Yangtze River basin, along the river and coastal cotton areas. The disease occurred in the whole growth period of cotton, and the damage was serious in seedling stage and bud stage. Cotyledons and true leaves were infected with purplish red at the primary edge and small gray round spots in the middle, and the later spots expanded or fused into irregular spots. Some concentric wheel lines appear in the center of the disease spot, on which there are small black dots, that is, the conidium of the pathogen. The disease part is often broken and scattered, when the humidity is high, the young leaves appear water-immersed disease spots, and then expand rapidly like boiling water, wilting and blackening, seriously withering and falling off, turning into light stalks and dying. Petiole, stem infected spot in the center light brown, surrounded by purplish red, slightly sunken, the surface scattered small black spots, serious stem branches withered or died. The disease spot of cotton boll infection is similar to that on the stem. The middle color is darker and black. When the humidity is high, the disease spot spreads rapidly, causing the cotton boll to become a stiff flap, and the boll cracking is incomplete or non-cracking.

The pathogen Gossypium Gossypium is a subphylum fungus. The conidium was initially buried under the epidermis of cotton plants and exposed on the epidermis after maturity. The spore organ is spherical, yellowish brown, with a slightly protruding round orifice at the top, the wall is thin and fragile, the size is 82.8-210 × 75-189 (μ m), and there are many endospores. Conidia ovoid, unicellular or bicellular, colorless, 4.5-7.3 × 3.5-3.8 (μ m) in size. The optimum temperature for the growth of the pathogen was 25 ℃.

The pathogen overwintered with mycelium or conidia inside and outside cotton seeds or in soil or manure with disease residue, infected cotton seedlings in the next spring, produced conidia in the diseased part, and released conidia to spread by wind and rain and aphids for re-infection. The temperature in seedling stage and bud stage was more than 20 ℃, and the overcast and rain lasted for 3-4 days. The disease may occur or spread within 3-5 days. In production, the low temperature and frequent rainfall often lead to the occurrence of the disease. APHIS gossypii is a serious cotton field, and the disease occurs seriously. The disease is also serious in cotton fields with continuous cropping and extensive management.

Control methods (1) seed treatment methods see black root rot of cotton. (2) strengthen cultivation management, implement reasonable rotation, intensive cultivation, seedling cultivation and transplanting, rational fertilization, promote cotton plant health and improve disease resistance. (3) pest control and disease prevention. It is predicted that the disease will be prevalent 1-3 days after rain, and when the number of aphids is large, spray 1 ∶ 1 ∶ 200 fold Bordeaux solution or 70% mancozeb wettable powder 1500 times, and add 1000 times of 50% dimethoate EC or 80% dichlorvos EC to control cotton aphid.