Heck, I don't know what it is either but the guy at Broward Orchid, who is pretty knowledgable about this kind of stuff (and he supplies it) said that was what he was going to do with his "palm trees". Hopefully it will stimulate growth of roots up closer to the leaves then I can cut off the "tree trunk". I'm going to get some next week at the Flamingo Gardens show in Davie, Fl.
I would think just about any rooting hormone would certainly help. Rootone is a powder and I would think would wash away once applied, unless you surrounded the area with spag. moss. I have a mokara and a vanda that had very long roots (30-36 inches) and I just trimmed them to about 12" and new roots developed on the leafless brown portion below the green leaves. When there is sufficient roots above the old roots I will shorten the entire orchid. Good luck with whatever you do. I do experiment some and never have lost one.
I've got the liquid kind, and some powder kind. I guess I could try to mix some of the liguid in my pump srayer and mist the bald area. Just dont know what else to do.