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Sarracenia seedling die-off question

I'm not new to growing Sarracenia, but I am fairly new to growing them from seed.

I successfully germinated a number of species this spring, and most seemed to be growing quite well ...

Until this week.

Most seedlings vary from seed leaves to beginning to put up their second true (carnivorous) leaf.

In most of the pots, there is now some degree of die-off. The seed leaves begin to turn brown, and then the pitcher does as well.

I desperately want to prevent this from spreading. Any suggestion?

Some additional facts (fwtw):

it's just starting to heat up here -- greenhouse temps hit 93 this week.

I've been spraying with a solution of rain water and wettable sulfur to keep mold at bay. Could this be the problem?

Seedlings are germinating on a layer of milled sphagnum (perhaps 1/2" deep) over peat/sand. Water is by tray from the bottom (except for the sulfur fungicide spray).

Can I stop this? How?

And if not, should I transplant the remaining healthy seedlings? And if so, into what? More moss? or peat/sand straightaway?

Thanks in advance for any information more experience seed growers can provide!
Jay, I'm not saying this is what is happening but do you have access to microscope or hand magnification lens? Might add some mosquito dunk chunks to those water trays which also control fungus gnat larvae and shouldn't hurt plants. If you tap the trays, do you see any little fruit fly sized adult flies fly around? Just guessing but could be fungus gnat larvae eating at your roots, again just guessing because sure it could be various things. Remove a portion of the soil and look through hand lens, should easily be able to see small midge looking larvae with black heads-fungus gnats, if not then you ruled that out but mosquito dunks are good to keep mosquitoes at bay anyway-I use them in my rain tanks.
I agree with DroseraBug about the fungus gnat larvae. They certainly are a common problem in young seedlings. The thing is, they really don't affect mature plants, only tiny seedlings, so they can go completely unnoticed for a super long time in the soil of mature plants, and then, when they get into your young seedlings, they feed off of the roots and prove to be harmful to the young plants. I had fungus gnat larvae in (luckily just) one cross of Sarr seedlings this past year and I didn't really pay attention to them, and of the maybe 30 sprouts I got, only one survived the infestation. Your mix sounds almost identical to what I use for my seedlings (I use LFS over a mix of peat and perlite). If they are infested, I would obviously repot, but not necessarily change the mix.

Another thing I might check is the amount of light they're receiving. If the leaves are crisping/browning up, it often means either a lighting or watering issue. Since it seems the trays aren't drying up, it doesn't sound like a water issue, so maybe distance them from the lights a touch.
Thank you both for the advice. I put a Mosquito dunk into the tray and will cross my fingers. If it looks like it is continuing to spread, I'll repot the survivors tomorrow. I stratified/vernalized the seeds in the greenhouse, and they have remained there since. Of course, the sun is getting higher/stronger than it was in February when I sowed them. I wouldn't think that the light would be a problem, but I can certainly move them under a bench if you think that would help.

D'oh! For some reason I read terrarium instead of greenhouse and thought you were growing them under artificial lights. My bad. No, you don't need to move them under a bench.
At 93 degrees you might have scorched them, especially if they're young and the roots aren't deep yet. Spraying them probably doesnt help either - sulphur is ok for rhizomes but you don't want seedlings sitting in a puddle of sulphur water I would have thought.

Sulphur is pretty ineffective anyway, plus your seedlings shouldn't suffer mould in a greenhouse with all that ventilation and light.
You can check for fungus gnat larvae by cutting a potato open and leaving it around your plants. It sounds weird but I've had success with it, they're quite attracted to it. You'll see these little clear worm-looking insects with black heads.

Might be a little late now but when you repot you should microwave the medium a little to kill any possible larvae. Hope everything works out!