Me too. Every year. I wonder if it is too low a light. I tried propping open the little tray lid with a popsickle stick and this seems to keep enough humidity and enough air as well. And the fan idea is a good. one.
The seeds themselves may have bacteria on them. I've been giving them a quick soak in 3% peroxide , and then a good rinse in running water. So far all is well. I got this info from the publications by Mr. Tom Landis from the US Forestry. He's the National Nursery Specialist. His publications are full of information about raising seedlings, soil & soil less mixes, light, pests, ect. ect. They're written about Pine & Spruce seeds to be raised for reforestation projects, but most of the information can also be applied to any seeds. I received his publications by emailing him to request a copy of each. Theses are beautiful books, free for the asking, and have indepth information. The first book is "Raising Forest Tree Seedlings at Home". There are 6 others available, and are listed in the back of the publication mentioned. Book 7 is in the works and I'm waiting for it to be completed so that I may have my copy. I now have a very complete reference library, thanks to Mr. Tom Landis! Check it out!
Tell him you were refered by Samantha.
A few years ago I found my seed flats were getting the same thing. Since then I haven't had any problems and I would think it's due to changing a few things. Now..I bottom water, run a small fan near the flats and I have better lighting. I did move some germinated seedlings this year out from under the lights and they started with some fungus. After putting them back under the lights, the fungus disappeared and the seedlings are growing very well. If you have too much dampness, combined with a cooler temp/little light, sitting over top of your soil line, I think those are the real culprits.
Hey, Michele5000 - do you leave your domes on your seedlings after they germinate? For how long? Hmmmm...I take mine off after they germinate - I've always been afraid of trapping too much moisture in there (shame on whoever decided that those new flats should be marketed with a picture of 6" tall seedlings, already in bloom, still growing under a dome!!!!) What does everybody else do with the lids after germination?
Dicentra, I think you are right about the main culprits.
I've had the most problems this year with the seeds that needed a couple weeks of room temperatures, then moved to cold or freezing temps, then back to room temps - nasty green stuff out the wazoo on that soil when it gets moved back to room temps.
I suspect it may be the seed starting medium itself (I "cheated" and used Jiffy starting mix, and didn't notice that it had fertilizer in it until I had potted up 75% of my stuff!) but have you ever heard of that happening?
Next year, all my seedlings will get started in my own mix - no more pre-mixed, bagged stuff for me (it's too expensive when you're potting up over a thousand seedlings, and it contains stuff that seeds just don't need, IMHO!)
Go-vols, I never get that far!I never let the lid just sit on the flat. I have to leave it propped open. The fungus starts right away. 2 days after I set up. I think Dicentra, has hit the nail on the head! Fan, more light, bottom water.And cool nights. I have just gotten the little kit with the bottom heating mat , and it seems to have made it worse. All my seeds failed this year! I will have to just plant outside. Sad but true.
Everyone seems to have keyed on the moisture issue and I think that's it too. It may be that your potting mix is too wet to start with. I make sure that mine is just 'damp',like a squeezed out sponge.I also bottom water only when they are
pretty much dry.I had damp off one year several years ago and lost everything.If I err now,it's on the dry side.
As far as the clear lids,if they have more than a light fog on them,your soil is too wet.Prop open the lids and let them dry out some.When your plants germinate,take them off completely.It is quite acceptable to not use the lids at all like Pete2.They work fine.
As for what I do with the lids,I use them for trays when I repot into larger homes.Most everything that I use gets a new home before it goes outside.