This looks really 'off', why are the pistils dead, it looks to be in very early flower?
I'm a proponent of the 'last thing I did' method. So:
1) Were the flower heads like that BEFORE you sprayed? Because if it was septoria, then septoria doesn't cause that.
2) If the answer is 'no', then I suspect your spray caused that. How much dripped into the medium? What is the pH of the medium now?