Answer: Blackened area on leaves may be caused by either sunburn or bacterial or fungal disease.
The appearance of black areas on the surface of the leaves, following a hot sunny day may be the result of sunburn. Exposure to direct mid-afternoon sunlight during the late spring through early fall will scorch the leaves of some orchids. Increase the shading or move the plant to a less sunny location.
If the blackened area increases in size, this is an indication of bacterial or fungal disease. Cut off the diseased area with a sharp, sterile tool(i.e., razor blade or knife). Then treat the plant with a fungicide like Physan 20.
Good luck with your orchid.
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