Bulbophyllums are giving me grief

[ArronOB]

Hi. I have about 40 orchids in 2 or 3 inch pots on our windowsills. Most are young cattleyas, but there are 4 bulbophyllums and although the cattleyas and oncidium types are in great health the bulbos all have problems.

There is a B. lasiochilum with a big pale patch. A B. lobbi gigantea with a chain of black spots, and a B. sikkimensis with a single black spot on a leaf tip. The photos below should be in that order. The 4th one is noid, multi-branched, and one new growing tip seems to be rotting off. It’s not really practical to photograph that fault.

Can anyone suggest the problem ?

Cultural notes: growing indoors in plastic pots, with pine bark medium. Watered frequently and weak fertiliser weekly. The cattleyas are dark green which suggests to me light levels are fairly low. Basically, the majority rules and they get treated like cattleyas. Minimum nighttime temp thru winter/early-spring on the windowsill was about 14 degrees Celsius (57farenheit) and max daytime temp was about 35 Celsius (95f) but that was only a couple of freak days. More normally about 25-28c. They got a brief winter rest through July and August. They’ll all go outside soon.

Thinking about it, I’m not a big fan of bulbos, so if there is any chance of them infecting my other plants then I’d rather just play safe and get rid of them. Can these issues spread to healthy cattleyas or oncids?

Cheers and thanks
Arron