Phased, I'm not a fungus expert. I'm a solutions expert. Corn meal seems to work on all the popular diseases except red thread, rust, and dog barf (yes, it's a type of fungus). I don't know why those seem to be immune. Dog barf goes away with a water hose, so that's the only treatment you need. Some diseases go away with shampoo just washing the disease microbes off the blades of grass. gotsqueeze, it's way too late to add seed for this season. But I like your thinking the problem through. I agree that the daily water needed for new seed might be a problem. Certainly if you were watering too long to the point of soggy soil it would be a problem.

Before dchall replies can you take him a picture from about 3 inches away. Get one of the grass that is still green at the perimeter of the brown area too. Also what is your definition of "water when needed" Debo you do seem to be reading my mind...or any of about 500 posts asking for the same thing. LOL. I've used corn meal successfully in St Augustine since 2002. There was one year when it seemed to be only good enough to stop the spread. This year might be one of those years. It has to do with how much rain we got since October. As Debo started to explain, corn meal works biologically. It attracts the Trichoderma fungus which is predatory on other fungi. It seems to feed on most of the lawn disease fungi, so it is considered to be beneficial. The application rate is 20 pounds per 1,000 square feet. It can take 3 weeks to see the new blades of grass coming out and not turning brown or getting spots on them. Here's what the spots look like. ...well for some reason GardenWeb is not letting me load a picture. Here's a link to the picture. I get corn meal at a feed store in plain brown, 50-pound, bags but you can also get it in 25 pound bags at grocery stores catering to the Hispanic population. It's something like Masa Maiz. Read the ingredients to see if it has any baking powder in it. You don't want or need that. Just get plain corn meal or corn flour.

Yes, corn meal should help you out. I have been successful with it for 15 years. You were watering at least twice as much as necessary. Here's more... 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. To put this into perspective, we had several inches of rain in the Texas Hill Country last May, and I did not water again until some time in late July. My soil probably holds moisture better than your soil, but the point is you are better off stretching out the watering interval than shortening it up. Deep watering develops deep, drought resistant roots.

Yeah when I asked that I realized the error of the question. We got 3 inches of rain but we got 5/8 one day, 5/8 the next, and like that. The problem was the fact that it remained moist for so long. 4.57 inches all at one time is fine, but when it is spread out over several days you get the diseases kicking in. I have had trouble with this one caused by continual moisture. You can try cornmeal, twice, and see how it works, but you might need chemicals. Or you can leave it alone and the winter should take care of it. Is it Floratam in full sun? If so it should slowly take care of itself.