greene said:Research a fungus named Magnaporthe poae and see if that could be it. Those most recent photos look like there is a fungus.
The grass in question is St. Augustine, which isn't a host of Magnaporthe poae. On St. Augustine it is more likely to be large patch aka brown patch (Rhizoctonia), or "Take-All" (Gaeumannomyces). It looks more like the former although I'm not sure about the mycelium, I didn't think one was supposed to see mycelium on large patch of warm season grasses. I don't see mycelium on the actual grass in the picture, though, it appears to be on whatever it is growing in (which doesn't look like ordinary soil??).
Edited to add this link I just found from the City of Austin on diagnosing lawn problems, it includes a flow chart (but also scroll down for pics of brown patch and take-all):
https://www.austintexas.gov/si...
