Control techniques of black spot of chrysanthemum

First, the main symptoms: occurs on the leaves, serious can spread to the petioles. The initial stage of the disease spot is grayish black spots, surrounded by a faded green halo; after expansion, the disease spot is nearly round to irregular, with grayish brown inside, blackish brown edges and yellow spots around; in the later stage, the center of the disease spot is yellow-brown and dry, and black particles will appear on the disease spot in wet environment. 2. Pathogenesis: Fungal disease. Pathogens survive in soil and plant debris, spread by wind and rain, watering, airflow, grafting, etc., and infect from stomata and wounds of plant leaves. Plant growth weakness, heavy soil viscosity, long-term rain and so on are easy to induce disease, seedling bacteria is the main factor causing serious disease. 3. Control methods: ① replace cultivation substrate, increase organic fertilizer and enhance soil permeability. (2) The cultivation substrate should be disinfected. The 500-fold solution of quintozene fungicide can be sprayed on the substrate for many times and used several days later. (3) In the early stage of disease, spray 600 times solution of zinc or thiram fungicide.