Received this. Cattleya several weeks ago, repotted it, just noticed some black spots.. fungus? Thought I would try to treat with physan 20 (purchased but have never used). Thoughts?
Probably it doesn't get dry as fast as it needs after watering. Temps bellow the recomendable, acting together with what I said previously, might be another factor.
If the lighting level and temperature levels are kept within satisfactory ranges, and there's adequate air-movement in the growing area ----- and also roots remain in a healthy condition, then the chance of these black patches occurring becomes quite small --- or even zero chance.
Littleflower - if those patches dry up or remain hard and don't grow in size, then it should be ok.
littleflower - some air-flow - doesn't have to be huge amount - can help in various ways. It can help cut-down or prevent fungal and/or bacterial growth on leaves, and on roots etc. Maybe a similar idea in a moist/damp bathroom that doesn't get enough air-flow inside ----- a buildup of mould etc, and the mold can also spread once they produce spores.
Air-flow can also help move air among the roots and media in the pot - if the media and pot and drainage etc are chosen suitably, which can help the roots stay healthy if a suitable watering schedule and method is applied.