HELP!! BLACK PATCHES ON DENDROBIUM!

[Roberta]

I think that is probably too cold for that species... It is from low elevations in the Philippines, and probably wants something like Phalaenopsis temperatures. Minimum around 15 deg C (60 deg F)and as much warmth during the day as you manage. This is just a guess on my part based on what I can learn about the species since I don't personally grow it. But if it is outside, consider bringing it into the house for more warmth.