Dendrobium nobile - black powder at stem joints
 

Hello!

Has anyone encountered this before? I am thinking it’s some kind of black mold? I sprayed it down with alcohol and am hoping that does the trick ...

Attachment 146550

It’s sooty mildew from honeydew secretions. Make sure you don’t have mealy bugs exacerbating the problem. Otherwise, just wipe it away with a damp cloth/paper towel.

Ok, that’s not so bad! Yes, I wiped it away before I sprayed them down :) I don’t seem to see any pests. Spider mites on my catasetums but that’s a whole other story!!

Is it an outdoor grower? I can't see from the pic, as the pic is relatively small. Does the orchid get some nice gentle air-movement? Air-movement can often cut down on fungal activity. And keeping leaves dry in some home-growing conditions (where possible) can help cut down that kind of thing too.

It’s an indoor grower but high temp (up to 95F+) and humidity (70%). I do have fans going all the time but all my orchids have been producing a lot of sap recently, so this makes sense. I will try to keep it away from the humidifiers.

I can't see the photo very well. The cane is very shriveled. They should not dry out this much. You may not be watering enough. Den nobiles need huge amounts of water during the growing season, and they should never dry out during this time. If underwatered leaves may die by turning black at the bases.