Symptoms are commonly referred to as "gray," "lower," and "upright." The disease mostly damages mature old leaves and develops from the bottom up. The pathogenesis of the leaves was as early as a round yellowish-brown spot. After the spots appeared white powdery spots, the lesions appeared carpet-like, the patches expanded, the white powder covered the entire leaves, and the diseased leaves turned green and browned. Withered. Severe damage to the stem, the disease stem is also covered with white powder. After the diseased leaves are baked, they are thin like paper, dark brown in color, and lose economic value.
Pathogen Erysiphe cichoracearum DC. Powdered fungus Asteraceae, belonging to Ascomycota subphylum fungi. The closed capsule has a spherical shape with a diameter of 85-144 μm and the appendages are mycelial. 6-21 ascospores, ovate or elliptic, base shortly stipitate, ascospore size 44-10723-59 (μm), containing 2 ascospores. Ascospores are colorless and oval in size 19-3811-22 (μm). The anamorphic state is Oidium ambrosiae Thum, known as Fusarium graminearum, belonging to the fungus Aspergillus spp. The white powder on the leaves and stems was the mycelium, conidial stems and conidia of the pathogen. Mycelium is colorless and has a diaphragm. Conidiophores are vertical to mycelia, size 80-12012-14 (μm), unbranched, shorter, terminal conidia. Conidia chain, unit cell, colorless, size 30-32.213.2-15 (μm). In addition to harming tobacco, the fungus also damages 15 species of plants such as sesame seeds, melons, potatoes, sunflowers, alfalfa and plantain.
Pathogens and Pathogens The pathogens overwinter on the diseased body with closed crust or mycelia. Winter in the temperate zone can also occur on hosts such as Solanaceae. In the following year, ascospores or conidia are produced and transmitted to tobacco leaves by wind, rain and insects for initial infection. The conidia produced on the lesions are re-infected. Partial application of nitrogen fertilizer, poor field management, less sunshine, heavy onset. Density in large fields, low wet soil in soil, and moderate humidity in the microclimate are conducive to disease. The powdery mildew grew at a suitable temperature of 16-23.6°C and was suitable for a relative humidity of 60%-72%. Humidity is too high, there is a suitable temperature for liquid growth 16-23.6 °C, suitable relative humidity 60% -72%. Humidity is too high, in the presence of liquid water can make conidia hypoxia.
Control methods (1) Selection of disease resistant varieties of flue-cured tobacco have Guanghuang No.10, Guanghuang No.46, Guanghuang No.55, G28, K326, DC202, F223, etc.; Sun Yanguang has Guanghong No.12, Guanghong No.13, F110 , F221, Lianjiang, Tang Peng, Jinxi smoke, etc.; burley tobacco has white ribs 21, white ribs 52, etc.; aromatic tobacco has a shell 44, Sampson and so on. (2) Strengthen field management Early planting, appropriate thinning, timely harvesting, timely removal of old leaves. Control the amount of nitrogen fertilizer application, increase phosphorus, potassium fertilizer, and enhance plant resistance to disease. Low-lying land is not suitable for planting tobacco, and it should be ridged when planting, and attention should be paid to moisture discharge. Do not apply organic fertilizer with sick body. (3) In the early stage of the disease prevention and treatment, 20% triadimefon EC 1000-1500 or 50% thiophanate WP, 50% carbendazim WP, 50% benomyl WP 1000 times, 50% Metalaxyl Sulfur Wettable Powder 500 times, 1.5% Polyoxin 150 times, 75% Chlorothalonil Wettable Powder 800-1000 Times, 40% Saprocarb Emulsion 500 times, 7-fold Spray once in 10 days and spray 2-3 times.
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