What is chrysanthemum greens downy mildew? What growers need to know
What is chrysanthemum greens downy mildew? Please provide an introduction and guidance on methods to control it. Chrysanthemum greens downy mildew mainly damages the leaves. In the early stage of the disease, pale yellow nearly round or polygonal lesions appear on the older leaves at the lower part of the plant, after which the disease gradually spreads to the middle and upper parts of the plant. In the later stage, the lesions turn yellowish-brown, and in severe cases many lesions merge into one, and the leaves...
What is chrysanthemum greens downy mildew? Please provide an introduction and guidance on methods to control itChrysanthemum greens downy mildew mainly damages the leaves. In the early stage of the disease, pale yellow nearly round or polygonal lesions appear on the older leaves at the lower part of the plant, after which the disease gradually spreads to the middle and upper parts of the plant. In the later stage, the lesions turn yellowish-brown, and in severe cases many lesions merge into one, and the leaves turn yellow and die. When humidity is high, a white mold layer forms on the underside of the lesions. The suitable temperature for the pathogen to infect is 15-17°C, and it requires a relative humidity above 85%. In autumn, with large day-night temperature differences and long frost periods, the disease occurs easily, and it worsens under foggy and rainy weather. In addition, overly dense planting, an excessively large population, excessive application of nitrogen fertilizer, poor ventilation and light penetration, or poor drainage will also aggravate the occurrence of the disease.
Control of chrysanthemum greens downy mildew: comprehensive measures should be adopted. In severely affected fields, a 2-3 year rotation with non-Asteraceae vegetables can be carried out; planting density should be reasonable, avoiding excessive dense planting to facilitate ventilation and moisture dissipation; apply heavy base fertilizer, increase the application of organic fertilizer, control the amount of nitrogen fertilizer, and prevent excessive vegetative growth; do not use flood irrigation, and drain promptly after heavy rain. In the early stage of the disease, you can choose 58% metalaxyl·mancozeb wettable powder at 500 times dilution, or Previcur 72.2% propamocarb hydrochloride aqueous solution at 1000 times dilution, or Sandofan 64% hymexazol·mancozeb wettable powder at 500 times dilution, etc., for spraying, once every 7-10 days, for 2-3 consecutive treatments. For fields under protected cultivation, chlorothalonil smoke agents can be used for fumigation control.
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