How often do you water? It looks like a fungus.

Since it's been like this for years, good new is that it's not Take-All Root Rot which can wipe out a lawn within a season. Otherwise yellow blades often a sign of poor iron uptake or lack of Nitrogen. There's a good summary here: Yellow St. Augustine.

Texas green sand is our primary treatment for iron chlorosis, but have also used Iron Plus - though response for these can be slow. Some spots can take multiple applications over 2 or 3 seasons to fully resolve. Applying a chelated iron foliar spray to a small area can confirm that iron uptake is the problem if it turns green. If you don't know your soil pH, a soil test would be helpful. Abnormally high pH can also cause problems with iron uptake.

PK I haven't watered at all this season until recently and then it is 2x week at 12 min per zone.

bostedo thanks for the feedback, I've applied ironite or some such suppliment a few years back when it first started and I think it might have helped a bit but didn't seem to really fix it. Whats strange is the other side of my yard across the driveway is fine so I'm skeptical it is the soil. I did have a soil test a couple years back let me dig that up to take a look at the pH.

I went ahead and applied a copper/neem oil spray yesterday to see if that will help if it is a funguns. I'll look into your suggestion on iron plus.

I will try to post a better pic that shows the 'area' of the lawn that is affected. Further back towards the fence (this is in the front yard) it is green and fine.

I am a big fan of agricultural grade corn meal for fungus, you get a mild feed too.

I second greensand. I had that problem at my last house. Within a few weeks of the application, the lawn was green again. It can be tricky to find though. I think I ended up getting mine at Barton Springs Nursery.

I've never had much luck dealing with fungal diseases, so I can't help you there...

Can someone link me to this Iron Plus you are talking about? I cannot seem to find it online

Hi Yield makes the iron plus Nitrogen stuff I was referring to and believe the linked article mentioned. Here's the Amazon listing.