That looks like a different kind of grass invading. Can you take a picture of that from 6 inches away on a cloudy or overcast day?

Looks like fungu:s. I would apply a fungicide and then top dress the lawn with peat moss: this should cure it

I couldn’t get cloudy or overcast but this is 6 inches away

Most defs not cloudy. I understand. It does look like disease.

Diseases in St Augustine seem to respond to an application of ordinary corn meal. I use it successfully every year. The application rate is 20 pounds per 1,000 square feet. Give us the name of your location in FL and I can direct you to the nearest feed stores to get corn meal in bulk. Cost should be well under $10 for 50 pounds. Don't use a chemical fungicide first (or at all). They should be used in cool weather, not summer heat.

What is your watering schedule? How often and for how long do you water?

When was the last time you fertilized? And what did you use?

I live in satellite beach. I water 3 times a week for 30 min with irrigation system. Perhaps I’m overwatering. I will get tuna cans out there this weekend to see how much water that 30 min actually is. I did just fertilize (well I had a company) a few days ago.

Call these feed stores to get pricing and availability. Obviously some of those are not feed stores, but Google thinks they are for some reason.

If you know about tuna cans, then you know you're overwatering. Once every 2 weeks is about right for your current temps. Also I assume you're in pure sand. Here's a picture of St Augustine growing wild out into the sand dunes in Port Aransas, TX. This area gets only rainfall. Even the mowed part only gets rainfall. And it doesn't rain that much there.

I suspected you are getting a liquid fertilizer. Your grass is too dense. That happens with frequent watering and liquid fertilizer.

I have a friend in your area. Must be a great place to retire. Is the humidity as bad there as the rest of FL?

Okay. I am in pretty much pure sand. I guess I’m just worried about only watering that little. I don’t doubt you in anyway I just don’t want to wake up to a dead lawn. Should I taper down or go cold turkey? We moved in this March and didn’t touch the watering schedule and when we moved in it was lush green. If you are confident I will listen and see what happens. From what I understand it’s easier to revive an underwatered lawn than an overwatered one. I’ll get the cornmeal this weekend and take care of it. If I spread all over lawn, even unaffected areas will it hurt anything? I really do appreciate your insight and knowledge. The humidity here isn’t as bad as we get the ocean breeze. I grew up in SA on the northwest side of town. I don’t think it’s any worse than that

It could be chinch bug damage.

Since you are starting with a stressed lawn, I guess I would taper off working toward longer watering and less often.

Use the corn meal over the entire lawn. It is a mild organic fertilizer, so it will improve the grass where it is unaffected by the disease.

Chinch bugs are a summer problem, not spring. They want really hot soil and usually start near concrete or asphalt where the soil is hotter.

So you think once a week in early AM for 1 hour?

I can't tell you now long to water. You have to do the can test and time how long it takes to apply an inch of water. Your water pressure and sprinkler system is different from everyone elses.