Little Backstory

Our 12 year old live oak tree's crown had gotten so massive, it became evident that we needed a more shade tolerant grass, as our builder installed Bermuda was slowly dying/thinning out, and the weeds were moving in.

We laid fresh Palmetto Saint Augustine grass, watered heavily instructed for first few weeks and the grass took root and was flourishing. We got tons of compliments.

Current situation:

Now, I'm noticing these brown circular patches/spots beginning to appear in certain areas of my lawn. I'm getting concerned, and I'm hoping someone here can help me.

The grass was installed on June 28, 2018. I've applied no fertilizer, amendments or additives of any kind to date.

Mowing on tallest setting. I live in DFW (Denton) to be exact.

We did get a LOT of rain about a couple weeks ago, but this week, it's been sunny with the high temps from mid 80s-90.

Please help.