Symptoms often occur at the seedling stage. At the beginning of the disease, the leaves became dark green water spots, followed by a brownish-brown spot. The center of the lesion was slightly sunken, white to yellow-brown, with sharp edges, slightly elevated and brown. When the wet spot occurs on the lesions and small black spots. The diseased tissue is old and hard when it is dry, and the lesions are mostly yellow or white with no ridges and dark spots. When the disease is severe, the lesions fuse into large spots, causing the tobacco leaves to shrink or dry. The veins, petioles, and young stems were spotted with spindles, browns, and longitudinal depressions. When severe, the seedlings were folded and the petioles were broken. In the adult plant stage, the disease often spreads from the lower leaves and gradually spreads upward. The culms are larger and the lesions are formed, forming longitudinal reticular reticular striae, depressions, dark brown, and the disease minister produces black dots when the climate is humid. Bracts and pods cause brownish near-circular patches.
The pathogen Collettrichum nicotianae Av. Sacca called tobacco anthrax, a fungus belonging to the subphylum Fungi. The black spot on the lesion is the conidia plate. Disk dense conidiophores, conidiophores short rod-shaped, colorless, unit cells, stems on the top conidia. Conidia are long cylindrical, colorless, unit cells, and terminal conidiospores. The conidia are long, cylindrical, colorless, single cells, with oil spheres at both ends. The bristles were mixed with bristles. The bristles were dark brown with a septum and slightly curved outside.
Transmission routes and pathogenic conditions The pathogens are mycelium and conidiospores that remain on the soil and manure as wintering with the diseased bodies, or they use the hyphae in the seeds or conidia to overwinter on the seed surface, becoming the first invasive disease in the seedlings in the following year. Dye source. The source of field bacteria is from diseased seedlings and soil diseased bodies. Germs spread by wind and rain. Conidia can only germinate when they are wet and only when water film is present. Tobacco anthrax mycelium suitable for the growth temperature limit of 5-35 °C, the optimum 25-30 °C, more than 35 °C less incidence. The incubation period is generally 2-3 days, and the low temperature incubation period is prolonged. Water plays a decisive role in the incidence of anthrax. Rainy days, heavy rainfall, poor drainage of seedbeds, dense tobacco seedlings, and excessive wet seedbeds are conducive to disease.
Control methods (1) Choose a non-heavy land with high topography, good drainage, and fertile soil as a seedbed. Use film seedlings, appropriate thinning, early seedlings, Dingmiao, less watering and choose sunny morning, avoid flooding. (2) choose to stay away from the soot, vegetable gardens, barns, and tobacco sheds. Apply adequately decomposed organic fertilizer. (3) Chemical control Before sowing, soaking with 1%-2% copper sulfate or 0.1% silver nitrate for 10 minutes, then rinse with clean water and sow again. Seedbeds were sterilized with pentachloronitrobenzene 5g/m2 or enemies 6g/m?2. In the early stage of disease, 75% chlorothalonil wettable powder 500-800 times or 70% mancozeb, 80% anthrax, 80% spray WP, 25% carbon WP, 500 times, can be sprayed. 50% thiodithiocarbamate or 50% TU wettable powder 600-800 times liquid, every 7-10 days, even spray 2-3 times.
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