I mowed the backyard (pictured) on Friday last week. I think last Friday the temp was upper 80's. Starting Saturday through all of this week it has been upper 90's-100's with high humidity. I haven't mowed since last Friday because was gone for work. Backyard is mowed at 2 inches I think. My front is at 1 inch and doesn't have any brown patches.... does look dry but not dormant. Not sure if I try to treat for fungus if that will do more damage given the heat we have right now.
I have seen some small isolated areas in the lawn that have a black powdery mold but that was a few weeks ago and mostly in the neighbors lawn.