Is it all the same type of sod? I do see what appears to be St. Augustine in the 3rd and 4th close up shots and I'm wondering if the issue might be thatch? We used to get thatch on occasion in our St. Augustine lawn but my husband had a de-thatcher attachment for the riding mower that he'd use to get the thatch and dead grass out. I'd rake that area to get the dead grass out and if you have a digging/garden fork you could aerate the space which might help.
If not thatch it could be due to fungus that happens in St. Augustine sod:
http://aggie-horticulture.tamu...
