How to prevent and cure the black spot of chrysanthemum?

How to prevent and cure the black spot of chrysanthemum? Please introduce that the pathogen is Alternaria chrysanthemum. Also known as brown spot, spot blight. It is a serious disease on chrysanthemum, which occurs all over the country. Symptomatic characteristics of the susceptible leaves initially appeared round or oval or irregular purple-brown spots of different sizes, and later became dark brown or black, with a diameter of 2 mm to 10 mm. The boundary between the susceptible site and the healthy part was obvious, and in the later stage, the center of the spot became shallow, gray-white, and small black spots appeared. In severe cases, only the top 2-3 leaves were disease-free, and the diseased leaves withered prematurely, but did not fall off immediately and hung on the plant. The pathogen overwintered on the residual body with mycelium and conidium, which became the source of infection in the coming year. The conidium emitted a large number of conidia, which were transmitted by wind and rain. Rainy autumn, high planting density and poor ventilation are all conducive to the occurrence of diseases. There are differences in disease resistance among varieties, such as purple lotus and mandarin ducks are more resistant, while the yellow disease in Guangdong is the most serious, the plant propagated by roots is more serious, and the disease is lighter when the buds are taken from the upper part of the healthy plant. Control method ① small area planting, artificial removal of diseased leaves, concentrated burning. ② improved the planting environment. Crop rotation should be carried out in areas with serious disease, and the planting density should not be too dense, so as to facilitate ventilation and light transmission, and eliminate stagnant water in time. During the onset of ③, spray with 100% 150 times Bordeaux solution or 80% dimethane wettable powder 500x solution, or spray 50% methyl topiramate 1000 times solution with 80% dicarbendan 500x solution, or spray with 45% chlorothalonil and carbendazim 1000 times suspension solution is better than single use. Click for more chrysanthemum planting techniques click to get more flower planting techniques