What are the control methods for southern blight in orchids?

This disease is a major hazard that causesorchidsto die. It begins in the plum rain season from May to June, with an optimum temperature of 25-35 C; in humid conditions plus stuffy, hot weather, the fungus can survive in dry environments for 3-5 years, with 2-5 generations occurring each year. Whereverorchidsare cultivatedand grown, this disease is present. Ventilation, sparse planting, isolation and burning of diseased leaves must be strengthened. Control methods: Because southern blight can infect the seedlings of many kinds of plants and reproduces quickly, preventive measures should be taken as the priority. 1. The soil used must be sterilized and disinfected at high temperature (100 C or exposed to blazing sun), and it is best to use soillesscultivationwith nutrient solution added, which is hygienic and harmless. 2. Organic fertilizers must be fully decomposed before application; switching to an inorganic nutrient solution is also acceptable. 3. Strictly control the introduction of the pathogen; isolate and handle diseased plants as soon as they are found. 4. Outdoors, prevent excessive rain exposure; indoors, control humidity during cultivation and pay attention to ventilation conditions. 5. When repotting or dividing plants, wash the orchid leaves and pots, and it is best to disinfect with a diluted potassium permanganate solution. 6. During the disease season, spray monthly with thiophanate-methyl at 800-1000 times dilution, or carbendazim at 500 times dilution. Two hours after using insecticides, spray the leaf surfaces once with clean water to remove the pesticide from the leaves and prevent burning the orchid leaves and seedlings. (Deng Shaokang)