So many problems someone help?

When a dendrobium cane turns black it is usually due to a disease causing agent gaining access to the interior of the plant and rotting it. Leaf fall, depending on when and where it happens can be due to disease, but it can also be part of the normal yearly cycle of the plant. Also when plants are moved from their growing place to another, the change in environmental conditions can prompt leaf loss. Another very common cause for leaf loss is root loss.

 

A cane that is black and mushy its beyond help. There could be the remote possibility that it is just the leaf sheath over the cane which is black and the cane under it is good. But this is not how things usually go. So if the cane has gone black, it has left this mortal coil.