Chrysanthemum planting: what is chrysanthemum downy mildew?

What is chrysanthemum downy mildew? Please introduce and guide the methods for the prevention and control of chrysanthemum downy mildew. At the initial stage of the disease, light yellow nearly round or polygonal disease spots are produced on the lower old leaves of the plant, and then the disease gradually spreads to the middle and upper parts of the plant, and the disease spots are yellow-brown in the later stage. in severe cases, many disease spots are linked together, and the leaves are yellow and withered. When the humidity is high, the back of the lesion produces a white mildew layer. The suitable temperature for pathogen infection is 15-17 ℃, which requires more than 85% relative humidity. Autumn day and night temperature difference, frosting time is long, the disease is easy to occur, foggy, rainy weather aggravated. In addition, too dense planting, too large population, excessive application of nitrogen fertilizer, poor ventilation and light transmission or poor drainage will also aggravate the occurrence of the disease. Prevention and control of chrysanthemum downy mildew: comprehensive measures should be taken. Seriously diseased fields can be rotated with non-Compositae vegetables for 2-3 years; planting density should be reasonable to avoid excessive close planting to facilitate ventilation and dampness; re-application of base fertilizer, increase of organic fertilizer, control of nitrogen fertilizer amount, prevention of overgrowth; no flood irrigation, timely drainage after heavy rain. At the initial stage of the disease, 58% nail cream ·manganese-zinc wettable powder can be sprayed, such as 58% nail cream ·manganese-zinc wettable powder solution, or 72.2% propoxur hydrochloric acid salt solution 1000 times, or 64% bad mold ·manganese-zinc wettable powder solution, etc., once every 7-10 days, prevention and treatment for 2-3 times continuously. The fields cultivated in protected areas can be fumigated with chlorothalonil. Click to get more chrysanthemum planting techniques click to get more vegetable planting techniques