Arghh!! 600 seedlings wiped out - what is going on?

[ScottinAtlanta]

Folks, In my 10th year of successful germination, my seedlings this year are destroyed by a mysterious death of the growing tip. The roots are fine - the stalks are straight, but the growing tips have died. See pic.

The only thing I did differently this year is wash the soil with hydrogen peroxide and mist the top with 50% HP solution to stop the dampening out problems I had last year.

Could the hydrogen peroxide have done this?

My first thought was heat from the lamps, but I use t12 flourescent bulbs and the heat was low, and the bulbs were not too close to the seedlings.