The symptoms are also called black spot and brown spot. The main damage to the leaves, the beginning of the brown spots on the lower leaves, after the expansion of the dark brown round or nearly circular to irregular spots, the size of a l0mm, the outside there is an obvious yellow halo. The edges of the lesions were dark brown in color and slightly faded in the center. When the humidity was high, there were not obvious small black spots, ie pathogenic conidia. In severe cases, the lesions fuse into a single piece, causing the entire leaf to become yellow and dry or dark, and some of the diseased leaves roll into a tube.
The pathogens Septoria chrysanthemella Sacc., called chrysanthemum and S. obesa Syd, are called chrysanthemums, which are all fungi of the subphylum Aspergillus. Chrysanthemum cruzi conidia Spherical to subglobose, size 51-78μm, brown or dark brown, wall material membranous, orifice diameter 12-17μm; conidial acicular or filiform, colorless, with 3- 6 membranes, size 23-431.1-1.8 (μm). The size of the conidia of chrysanthemum was 66-160μm, and the length of conidia was 44-108μm, which was greater than that of Chrysanthemum. Chrysanthemum chrysanthemum grew slowly on PDA medium, colonies were dark brown and hemispherical and dense. It grows well on oatmeal medium and has large colony diameters. It can reach 13mm in 63 days of culture and has more spore production. The time required for spore production at 20 to 24°C was 16 days, and that at 12°C and 28°C was 37 days and 21 days, respectively; conidia did not germinate in clean water or the germination rate was very low. Conidia germination temperature limit 12-32 °C, germination temperature 26-28 °C, 55 °C after 10 minutes to death. Conidial germination requires water droplets or water film and sufficient oxygen, otherwise germination does not occur even if the relative humidity is close to saturation. The range of pH is from pH 3 to 11, and pH 5-7 is most suitable.
Transmission routes and pathogenic conditions The pathogens overwinter on diseased bodies. When the conditions in late spring are appropriate, the pathogens are transmitted by wind and rain. After 20 to 30 days of incubation, conidia are produced again for reinfection. The conditions of high temperature and rainy conditions are prone to disease. In southern China, the warm and humid climate in May-October is apt to occur, and the incidence in the north is high from August to September. In addition, the incidence of flower beds in continuous cropping, planting dense plants and planting old roots is heavy.
Control methods (1) selection of disease-resistant varieties. (2) The onset of disease must be strengthened. Watering amount, choose to sunny morning watering, cloudy or not pouring. (3) Apply compost from enzyme fermentation to avoid partial application of nitrogen fertilizer. (4) Appropriate planting density, timely drainage of gutters, ventilation and light transmission, timely removal of diseased leaves buried or burned. (5) Spray 30% basic copper sulfate suspension 400 times or 1:1:100 times Bordeaux mixture, 80% Capitacum wettable powder 500 times, 50% thiophanate-methyl suspension 800 times liquid, 75% chlorothalonil wettable powder 600 times, 50% benomyl wettable material l500 times, every 10-15 days, old plants or into the reproductive growth every 7-10 days 1 times, depending on the condition of prevention 3-5 times.
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