I've had this ventricosa for almost a year now, and it's been doing great. Two lower leaves are yellowing, and I first thought it was just age. A few days ago, however, I noticed that the oldest leaf has a very dark tip to it, as if someone covered it with charcoal dust. All the other leaves look unaffected, but I'm just scared that this is root rot or burn.
I have it in 50% humidity, 77F days and 73F nights (sometimes the day temps can go up to 80F, if I bring it outdoors). It's potted in a bark/spaghnum/peat mix, and I usually water until the top of the moss is pretty dry. No fertilizing, and I water with rainwater. It's in medium sunlight (around the same lighting Oncidium orchids like)
Here's a photo :
Untitled by Dante1709, on Flickr
Is this just the natural aging of the leaf, some type of fungus or root rot? It happened pretty rapidly (within a week, at the most) since I haven't noticed it before.