Dendrobium Leaf Drop & Blotchy Leaves

[DSDNYC]

My Dendrobium Yellow Chinsai 'Little Joe' was growing quite well until late-summer with lots of new growth and green leaves. Over a short period, I noticed numerous black leaf spots followed shortly thereafter by leaf drop. I suspected fungus, and treated with Photon 20 Situation seemed to improve, though I'm not convinced all is well.

With the arrival of cooler weather, I cut back watering as I normally do with this orchid, but even a small amount of water every few weeks cause massive leaf drops. I'm clearly not this orchid's best friend.

Help appreciated.