Dendrobium with black mold (?) where leaves meet cane
 

Hi everyone! I’m new on this board so I’d like to thank you in advance for any advice and/knowledge you can share with me.

I bought this den nobile (my very first) and it was gorgeous when it arrived. Tons of white blooms all over! But then in a couple of days the flowers wilted and fell off. Possibly the shock of the travel?

And now a week later I find it’s got this black dusty mold where the leaves meet the cane. Does anyone know what it is? And if so, how I can fix this??

Thank you!