Detailed Explanation of Leaf Spot Disease in Oncidium and Related Orchid Genera

① Harm: This Cercospora fungus can infect Oncidium and related genera oforchids, including some species and hybrids. Under normal circumstances, the damage to plants is very small, but occasionally it can be severe. Besides Oncidium, other related host genera that can be infected include: Comparettia, Mitonia, Rodrettia, Rodricidium, and Rodriguezia. ② Symptoms: The symptoms initially appearing on the underside of the leaves are sunken light reddish-purple spots with a slightly raised center that is light brown. Individual lesions are usually less than 1mm in diameter. As the lesions age, the entire lesion becomes sunken. If two or more lesions coalesce, they eventually become sunken light reddish-purple spots that can reach several millimeters in diameter. The corresponding areas on the upper leaf surface turn yellow-green. ③ Control: Spray 3 times with 50% benomyl wettable powder at 1000 times dilution plus a small amount of wetting agent, once every 2 weeks. After that, if necessary, spray once a month. Liu Zhongjian