Seedlings going down fast - help!

[jholland]

Hi - I am growing about 70 heirloom seedlings under grow lights they were all planted in organic seedling soil and have had not other additives/fertilizers etc. The plants range from 2-3inches high.

Last week several of the seedlings had their bottom leaves dry up and fall off and I thought perhaps I had just set the soil get too dry so didn't worry too much. This week all the plants have had their bottom leaves fall off. Upon closer examination there are tiny purplish (maybe black?) dots on the leaves and the tips dry up, fold in and eventually fall off. On some plants the bottom leaves are turning yellow and falling off. The top leaves of the plants seem fine and the base of the plants are straight and strong but the bottom leaves continue to fall off....some of the smaller plants are down to one leaf!

I have been growing these plants for a plant sale that is in a month and am in a panic because it doesn't seem to quite meet any of the diseases that I've read about but I'm not sure if its a nutrient issue either.

If any one can help me identify what is going on and hopefully save the plants I would appreciate it.

PS. I was planning on transplanting the seedlings to larger pots and starting to harden them off since our weather just started to stay above freezing.