Steve, If you have a grub issue the grass should pull up from the soil very easily, almost like pulling up carpet. Grubs are active from about june thru october, so it could very likley be that. I would pull up a 1ft by 1ft section and dig around to see if you find any grubs.

Great picture! Thanks. I see tufts of dark green spots. Do you have a dog? Or are these the spots that have not yet been affected by the brown patch??? If you have a dog and have those tufts, then that indicates you are seriously behind on your fertilizer. It would indicate that the urine from the dog is providing more fertilizer than you are. I'm not surprised you water that much. You said you had short little roots. What will happen eventually, once you get the disease under control and get some microbes working for you, your roots will grow much deeper and will be able to get moisture from deeper in the soil/sand. Hopefully you'll be able to back off on the watering some, but not now. I haven't seen anything that would make me change the frequent corn meal application suggestion. I guess I would tend toward monthly applications until your sand starts to turn dark brown. I use white sand as fill in my yard. Eventually it will turn very dark with organic matter. Here's a link to the Texas Plant and Soil Lab. Tell them you are organic and they will help you out. These folks have performed miracles in agriculture. The reason they can perform miracles where others have failed is they use the same chemicals for testing that the plants use in the soil. They don't use hydrochloric acid to dissolve everything and see what's left. They use carbonic acid like that found in the soil. The result is that when they tell you what soil minerals are available to your plants, they can back up their recommendations with analysis of the plants themselves to show what minerals are being taken in. You can't do that with hydrochloric acid testing, and that is why I'm so negative on university soil testing. Universities know how to do the tests like TPSL does, but they choose not to. Even if you demand carbonic testing, they have to $$$pecial order the materials and refresh themselves (i.e. learn) on how to do the tests. And then they have no database using carbonic acid, so they cannot interpret the results. Furthermore, they are still going to suggest you add chemicals to your garden because they are, by and large, unaware of what organic fertilizers are. Whereas the TPSL routinely does carbonic acid testing so they order their chemicals in bulk to get the cost break, they know how to do the tests, they know how to interpret the tests, they provide more testing than the universities do, and they will give you recommendations in line with an organic program. If I recall they charge $35 which is a few dollars more than the universities. Here is a link that might be useful: Texas Plant and Soil Lab

Chinch bugs strike first at the hottest part of the lawn. Usually that is in a corner where the hot driveway meets the hot sidewalk. If you've been getting a lot of rain, it likely is not hot enough for chich bugs. Have you had some clear skies for a couple of weeks to heat up the soil? Otherwise my first thought was fungal disease (lots of rain). Can you post a picture? The best pictures are taken in the shade or on a cloudy day. If you could get one close up at about 3 inches away showing both green and yellow or dead grass blades, that would be very helpful.

See the tan colored spots with the dark brown edges? Those are fungal disease spots. That's what's taking out your grass. This should respond to ordinary corn meal if you have not already applied a fungicide. Call your local feed stores to find it in 50-pound bags. If they don't have it you'll find corn flour at any grocery store in FL and especially those that cater to the Hispanic population. If you get it at a grocery store there are different products packaged in very similar bags. You don't want the stuff that already has baking soda/power in it. Apply at the rate of 20 pounds per 1,000 square feet. Apply to the entire lawn or else you'll have green spots. Corn is a fertilizer. The reason corn meal works against fungal disease is through the decomposition process a predatory fungus takes over the final stages. Once the predator finishes with the corn meal it takes over killing the disease fungus in your yard. This is a biological process that takes about 3 weeks. You can apply in the heat of summer or whenever you feel the need. During the 3 weeks you should see new grass coming in but it might still get the spots. After 3 weeks the new grass should not get the spots. Most people in FL are watering wrong - at least the ones writing in here report that everyone waters every day. That's wrong. 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.