What do you mean by well watered?

He uses water that comes from a well.

Actually I just mean I water it what seems like a lot to me ha. Usually for an hour-hour and a half on days it does not rain. We actually did get several days of hard rain in a row about a month ago. I will take a closer picture asap

Without seeing the picture I'll tell you now it's a fungal disease caused by too much watering.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

With St Augustine I think you can go cold turkey in changing from frequent shallow watering to deep and infrequent. When you test your sprinklers to determine the time to put out 1 inch, that will be the first deep watering. Then see if the grass will go a full week without the blades folding together. If they fold together in 4 days or less, then water it deeply again right away. Fixing the watering is the most important thing you can do with your lawn. For some reason everyone in Florida and California think you have to water daily. Not true - in fact it's counter productive.

You'll need a chemical fungicide to fix what you have. The organic fix won't work on this disease.

Thank you very much for all that information. I was definitely wrong thinking watering everyday was necessary in this heat. I will test out the watering time and adjust my watering.

As for the fungicide, is there a particular type that you would recommend? Would they have what I need at a home depot or lowes?

I have also added the picture to that link

Thanks again for the info!

You seem very knowledgeable, so I have one more quick question. I have been mowing once a week at about a 2.5" height. Does that sound correct for St Augustine?

Mow at your mowers highest setting. It should be around 4 inches.

That definitely looks fungal. My guess is brown patch.

This is not from a big box store but is actually cheaper than what you would get there.

https://www.amazon.com/Propiconazole-Honor-Guard-Spectrum-Fungicide/dp/B015X6FIYS/ref=sr_1_1?ie=UTF8&qid=1466803539&sr=8-1&keywords=honor+guard

It has to be sprayed with a pump sprayer. If you only want from a big box store, Bayer Advanced Fungus Control rts (the liquid) is the same active ingredient but less percentage (14.3% vs. 2.4%) for about the same cost.

https://www.amazon.com/Bayer-Advanced-701270-Control-32-Ounce/dp/B0035KNZJU/ref=sr_1_1?ie=UTF8&qid=1466803691&sr=8-1&keywords=bayer+fungus+control

You can get more applications out of Patch Pro as well so a much better deal. So Patch Pro is what I would recommend for a cheap option. Heritage G probably works better but it is $85 for a bag.

Also be aware that you need to rotate fungicides from different classes in order not to build up a resistance. You can use Patch Pro today (class 3), but rotate with other classes if you get fungus issues if the future (Heritage is class 11, thiophanate-methyl based such as Cleary's 3336 or Scott's is class 1, etc.)

Check the directions to be sure it is safe for St Augustine and that it is safe for the temperatures you're having.

Always mow St Aug at the mower's highest setting. I tell people to weld their mower at that setting so that some well meaning neighbor doesn't do you a favor and mow it short for you.

All the ones I listed are safe for St. Augustine (and I have used them on my St. Augustine grass with no damage). The Bayer rts says not safe above 85 degrees, Patch Pro said not above 90 on golf course bermuda (though same AI as Bayer), Heritage did not have a temp restriction.

Any updates on your St. Augustine?