Browning and blackening of leaves

[SundayGardener]

Looking at your initial pictures, I have orchids that look exactly the same. Over the past year, I have been able to rule out watering issues (over or under watering) and bacterial infection.

In some cases, specifically for catts, increasing calcium in the water and adding oyster shell to the potting media helped.

In a few cases, moving the plant to lower light helped (but the damaged areas of the leaves remain).

I definitely have a fungal situation, and dendros are particularly susceptible. For those, so far the only fungicide that has made a difference has been mancozeb.

I have also tried diluted rubbing alcohol on leaves where I suspect insects, and pesticides containing imidacloprid for suspected mealy bugs.

I typically remove the damaged portion of the leaf or the entire leaf for containment.

Although I have different varieties of orchids with black and brown spots, I suspect they have different ailments. The dendros are the least able to cope, while the catts rally and carry on.

By the way, I also use Garden Solutions and K-Lite and kelp...