Bulbophyllum orthoglossum and carunculatum not doing well-new growths keep dying :-(

[brammn]

Hi,

I have one of each of these plants and I'm not completely sure what I'm doing wrong - I have 5 Bulbo's in total and the other 3 seem to be fine
The one has dropped all of it's leaves and the other one isn't looking so good (the orthoglossum is the one that has dropped all of it's leaves).
They both keep trying to push up new growths, these get to about 3-4 cm's then go black and mushy and die. I've attached photos of the condition they are both in at the minute. The orthoglossum is trying to push up a new growth - I'm hoping this one won't die!
I've tried them in a variety of conditions - in the greenhouse, under grow lights, they're now on a north facing windowsill
Any thoughts anyone - I'm really keen to save them both and get them both growing on so they hopefully flower.
Thanks
Nathan

[Discus]

what temperature, humidity, light and watering regimes have you been using?

[brammn]

Thanks for replying
Watering is whenever they dry out, temperature varies - in the greenhouse at the moment it goes up to about 32 celsius and drops to about 16 at night (greenhouse is South facing so it gets full sun all day), under the lights it goes up to 28, then drops to about 16 (light is a 300w LED - it's enough to get Vandas and Cattleyas flowering so it is pretty meaty), where they are now goes up to about 25 and drops to about 18 (they're on a North facing windowsill now)
humidity in the greenhouse is between 50 and 70%, under the lights about 70% and where they are now about 50%
I feed probably every 4th watering - is that enough, are they heavy feeders?
Thanks
Nathan

[Discus]

By the look of that leaf (fungal/bacterial problems) you're either growing them too damp (humidity wise) or there isn't enough air circulation.

Most bulbophyllums seem to be relatively low light plants (particularly compared to e.g. vanda/cattleyas which are high light plants) so it's possible they're being scorched too.

I take it you've read things like
IOSPE PHOTOS
IOSPE PHOTOS
for cultural requirements?

Incidentally, the latter page suggest *both* these plants are B. amplibracteatum.

---------- Post added at 02:07 PM ---------- Previous post was at 02:02 PM ----------

I have a few Bulbophyllums; I don't generally let them dry out as they don't seem to enjoy it. The mounted ones have especially enjoyed the addition of sphagnum to their mounts, and they get watered almost daily.
I'm by no means an expert on this group - I've only flowered one of them!
They're not near a window and face away from my lights (although the ones near the T5s are starting to grow around the back of the mount and leaning in toward the light, so perhaps they can take more light than I thought).

[brammn]

Hmm, interesting - thanks for the reply. I think I'll leave them where they are now then as the humidity is a bit lower, and being north facing the light is not quite as fierce - see how I go.
I'll also up the water a little bit and also try increasing the fertiliser see what happens
Thanks for the advice

[Discus]

Don't change too many variables at once - leave your fertilisers as is (what dose rate are you using, incidentally?).