Hello April,

go to Jay's species orchid site and read what is said there. I think you will have to modify your culture, those black leaves might say fungus but they are also a sign of not optimum growing conditions.

I do not have this species, but I do have very large collection of Cattleyas and never mist any of them. They have those pseudobulbs to store nutrients and water between watering intervals.

Sure they are watered, but only in the early morning and not every day.

Nobilior are a favorite species of mine and am glad you have yours mounted. Looks like in some areas other than what you think may be rot, is a general yellowing that may resemble sunburn. Have you changed location of plant to a much brighter spot? maybe, kjnda suddenly? to possibly cause a bit of sunburn?

I would take pictures of damaged area every couple of days to compare and see it grows, in which case you should be concerned and may need some anti rot chemical gun... if there is no growth of dark area, it should be fine. Try to keep in well ventilated area so it dries quickly after watering. I used to water my mounted walkerianas and nobiliors daily and was generating some killer blooms. For a small plant it blooms its heart out... if its happy...