The symptoms are also called early blight. Located in Liaoning, Hebei, Yunnan, Hunan, Henan, Jiangsu, Fujian, Taiwan and other places. Occurred mainly in the mid-lower leaves of the tobacco plant from the long-term to the mature harvesting period, and had a round or irregular shaped gray or black spot, a narrow yellow halo or none, a size of 3-20 mm, and a multilayer wheel. Lines, sometimes with gray mold layer, that is, conidial stems and conidia of pathogens. The lesions are easily broken under dry conditions.
Alternaria tenuissima (Fr.) Wiltsh synonym A. Tabacina (Ell. et Ev.) Hori is called Alternaria spp. Conidial stems linear, dark brown. Conidia are stick-shaped, dark brown, 42-70l0 in size 18 (um). In addition, Alternaria solani Sotauer is said to be an aetiological agent of Alternaria solani.
Transmission routes and pathogenic conditions The pathogens overwinter in mycoplasma and conidial plexus in the diseased area or in the soil left over from the diseased body. In the following year, conidiospores were produced by airflow or rain spattering for initial infection and reinfection. The bacteria in the south have spread around the host and there is no wintering problem. Usually warm and humid weather or densely planted ecological environment is conducive to the occurrence and expansion of the disease.
Control methods (1) Proper close planting, clean ditch, pay attention to improve the ventilation conditions to reduce the temperature. (2) After the growing season is over, the disease is completely collected and burned to reduce the bacteria source. (3) 70% chlorothalonil wettable powder 1000 times solution plus 70% mancozeb WP 1000 times solution, 80% spray WP wettable powder 600 times solution, 80% Xinwansheng Wet powder 600 times, 40% chlorothalonil suspension 500 times.
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