I think its Brown Patch?
I don't treat for lawn fungi, but I seeded my own lawn about 3 weeks ago and I noticed several spots about the size of a doughnut, where the grass has turned black and died. Also, I can see small web-like areas at the base of the grass, looks like frost growing on the blade. Monday and Tuesday we had a really, really humid air mass and rain both days. After this is when I noticed it.
This is the first time I have seen this. Can I spray anything on it this early to stop it? Treatment?