Thanks Rocket. I just peeled back a very large fat sheath on one of my BLC's and found some really nice ....BLACK GOO!!!!!!!!!! ARG!!!!! Oh well. It's been quite a time getting this one to even grow new pbulbs so maybe another year and it'll be better.
I usually see some form of discoloration in the sheath. If I cut the sheaths off on the end it usually helps them. It is moisture in the sheath and it sets up some sort of fungal crap. Irritating to say the least. It could be high light hitting the sheath and causing moisture to condense.
NY, I've watched for many years how the flower sheaths push out and grow just to have them rot in-sheath. The only commonality is moisture and sunlight. They stay closed with no apparent break in the sheath yet still sometimes become black and rotted. Sometimes they turn pinkish or reddish which tells me they are rotting. When I cut open the tops of the sheaths I don't get that condition. Most of the time when sheaths start to really plump up I curtail watering normally. When I do that, again I get no rot. Remember mine are almost always in some state of rehabilitation. It's just annoying when I wait for a long time for something to bloom and at the end have rotted flower buds. Oh well.