Clumps of yellow balls of fungus on medium surface
 

A new day, a new discovery. Today it's clumps of small yellow balls of fungus (presumably) on the surface of my dendrobium's medium. Does anyone know what this is specifically, and whether it's something to be concerned about? Should I just reduce watering and hope that drying it out a bit will kill the fungus off?

Drying will not kill the fungus. The spores can sit around bone dry for years, then germinate upon contact with moisture.

Certainly you can treat with a disinfectant, but that potting medium looks pretty old, and likely needs to be replaced.

Yes, I was wondering whether I should repot. OK - thanks, Ray.