The symptom is also called snake eye disease. The main damage leaves. The lesions are round, brown, brown, or dirty white, with narrow margins and dark brown. The center is grayish-white parchment-like, which resembles a frog eye. It is called "frog eye disease." Due to different environments and species, lesions are sometimes polygonal, with little or no central white. When the humidity is high, a gray mold layer is formed on the lesion, and when the disease is severe, the lesions merge and cause the entire leaf to die. Green leaves or dark spots may form during the baking of leaves infected 2 to 3 days before harvesting.
The bacterium Cercospora nicotianae Ell. & Ev. is called C. nicotianae, a fungus belonging to the genus Deuteromycotina. Mycelium is colorless, septate, conidiophore brown, curved, l-3 separate, bundles of Health. Conidia are slender, colorless whip, straight or slightly curved, base is thick, with 5-10 diaphragms, no mediastinum.
Transmission routes and pathogenic conditions The mycelium was overwintering in the soil with the diseased body and became the source of the dip in early. Contaminated spores were reinfested with wind and rain. The optimum temperature for pathogenic bacteria growth is 27-30 °C. High temperature and high humidity are favorable to the onset of disease, low-lying terrain, poor drainage, over dense planting, and poorly permeable tobacco fields.
Prevention methods (1) Implement 2-3 year rotation. (2) Early nursery, early transplanting, and timely harvesting to prevent over-ripening leaves. To improve baking temperature, heat at 38-42°C. (3) Pay attention to field drainage, strengthen management, and have a reasonable density. Apply adequate fertilization of organic fertilizers using formula fertilization techniques. (4) After the tobacco field is harvested, remove the diseased body and deep-dip. (5) Chemical control Spray 1:1:100 times Bordeaux mixture or 50% carbendazim wettable powder 600-800 times solution, 70% Mancozeb WP wettablet 500 times before transplanting to reduce the disease . In the early onset of the field, in addition to the above three agents, it is also possible to use 40% extermination of the disease Wei Suojiao 400 times liquid, every 7 to 10 days once. 150 times liquid, 50% fast keratin or 50% acetaminophen wettable powder 1500-2000 times, 75% chlorothalonil WP 800 times, 12.5% ​​speed Poly WP 2000 times, 40 % Sclerotium net wettable powder 400-600 times liquid, can also be 1:1: 150-200 times more Bordeaux fluid control, liquid spray evenly, it is best to use alternately to prevent the emergence of drug resistance. Every 7-10 days, control 3-5 times. After the spraying, it rains. After the rain, it needs to be sprayed.
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