Detailed Explanation of Leaf Spot Disease in Vanda Orchids

① Harm: Known hosts of this pathogen include: Vanda, Aerides, Arachnis, Ascocentrum, Doritis, Phalaenopsis, Rhynchostylis, Aeridovanda, Ascocenda, Renanthera, etc. ② Symptoms: The lesions on the underside of the leaves are very small, generally less than 1mm in diameter, sunken, and purple-brown in color. Several small lesions may merge into larger ones. Once primary infection occurs, many small lesions are produced. Usually, due to intermittent growth of the mycelium within the leaf tissue, these lesions arrange themselves in a circular pattern. If no control measures are taken, the entire underside of the leaf will be covered with small lesions. Because the pathogen enters the plant through the stomata, the corresponding areas on the upper surface of the leaf turn yellow-green and may eventually become purple-brown. In severe infections, the leaves may die or drop off. ③ Control methods: Prepare a 1000-fold solution using 50% wettable powder of benomyl, add a small amount of wetting agent, and spray 3 times at intervals of two weeks. After that, if necessary, spray once a month. Ferbam can also be used to protect healthy tissue at a concentration of an 800-fold solution with an added spreader-sticker, applied once every 2 weeks. When conditions permit, all diseased leaves should be removed and destroyed. (Liu Zhongjian)