Angela: I've been fighting something like this for the last year or so. I've shown it to several orchid people (on forums and elsewhere), and it's surprising that I get so many different opinions of it. It has particularly devasted my dendrobiums, bulbophyllums and thin-leaved plants. I'm going to treat it as a fungus or bacterial problem and am going to hit it with Bayer Advanced 3in1 according to instructions (i.e., spray three times every 7-14 days). I'm also going to sanitize the greenhouse with a peroxide-based spray and put fungicide in the evaporative cooler. If that doesn't work, I'll have to focus on slipper orchids which seems to be the only group that isn't affected by it.

Needless to say, I feel your pain.

wuness