Welcome to lawn care...and stop watering!! You are killing your lawn with kindness. I'll explain. Look carefully at this picture.

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See how the spot forms an oval right in the middle of the drainage swale? What you have is standing water right there that has contributed to a fungal disease. I'm going to make the wild assertion that all your dead grass is due to a fungal disease simply because you are watering wrong.

St Augustine grass, especially in Houston and especially this time of year, only needs to be watered once every 10 days or so. You are watering more like you were establishing a new lawn. Now you need to back off. I would wean it by skipping days and increasing the time. To start with you should water about an inch every time you water. Measure how long it takes to fill a tuna can using your sprinkler system. Then water for that length of time when you water. Watch the grass for signs of wilting to get the timing for your watering. Sometimes you can go 14 days in the spring and fall. In the winter go to a monthly schedule even if the grass is dormant. When the summer heat cranks back up, you can go to every 7 days and maybe to a 5-day schedule if 7 isn't working. The big point is that you are watering shallow and often. You should be watering deep and infrequently.

Frequent watering is also the reason for your weeds. Grass and weed seeds need frequent watering in order to sprout. By backing off on the watering you will cut off the supply of water at the very surface of the soil and virtually stop the new weeds.

The reason your attempts to kill the weeds has not worked is you are using the wrong product. Weed n Feed comes up in the forums all the time. It just doesn't do what you expect it to do. The reason seems to do with timing of the product. Weeds die best when they are well fertilized. But by the time the fertilizer part of the WnF product kicks in, the herbicide is long gone. You will have much better results using a plain fertilizer at the recommended rate and then, spot spray individual weeds with something like Weed-B-Gone two weeks after the fertilizer. You will also save a lot of money and frustration. If you want to try that again but you're afraid of killing the grass with too much fertilizer, you can use organic fertilizer instead. The two types of fertilizer have absolutely no cross interactions that would cause you to worry. But in the case of organic, it takes 3 full weeks to see results, so wait 3 weeks instead of 2 before you use the WbG.

The last thing with St Augustine is to keep it mowed at the mower's highest setting. There is never any reason to lower the mowing height of St Aug.

One more last thing, whatever that weed is should die out from Weed-b-Gone. Be sure to use the Weed-b-Gone in the black bottle with the purple label. That is the only one safe for St Augustine. But do not spray and breath the spray or get it on your or pets. Keep the kids and pets away until it has dried. The less of that you can get away with using the better.

Your lawn looks very good, by the way...except for the minor amount of dead stuff. We see some pretty crappy lawns in the forums. Hopefully yours will never become one of those.

Thanks for the advice dchall. I'll start skipping days and increasing the watering time. I measured how long it takes to get an inch of water in a can. It took about 48 minutes. That means it would take about 6.5 hours for all 8 zones to run. My concern is that I will get a lot of run off since the rate of water absorption will not be fast enough during the 48 minutes of watering per zone. What schedule would you recommend to avoid runoff?

Also, should I use a fungicide or just let the grass recover by itself after watering has been adjusted?

What organic fertilizer do you recommend?

Thanks again! I really appreciate your help!!

If you get runoff then you need to soften the soil. There are soil softening products on the market that involve soaps and organic surfactants like yucca juice. Those work fantastic to help the water penetrate more quickly. You can save a lot of money by spraying generic baby shampoo every 2 weeks for the next 2 months. I would figure about 3 ounces of soap in a hose end sprayer for every 1,000 square feet of grass. Spray it until the soap is gone. It doesn't matter what setting you put on the sprayer as long as you measure it right going in and use it all up evenly over the area.

Your soil should naturally become hard toward the end of the dry period before you water again. For example if you normally water on Friday, the soil should be very soft on Saturday and Sunday and gradually firm up until is seems pretty hard on Wednesday and Thursday. But, like a sponge, it should soften quickly when you get it wet. This has nothing to do with compaction. If your soil remains hard even after you water it, then you need the soap or surfactant, not necessarily a plug aerator.

The organic fertilizer I have used for many years is ordinary corn meal. This year the Chinese bought all our corn so the cost went way up. This year soybean meal became my fertilizer of preference. Otherwise it would have been alfalfa pellets (Purina Rabbit Chow). The app rate is 20 pounds per 1,000 square feet. The more often you use it the better the soil and lawn will perform. There is no maximum that I am aware of. One of the gurus on another forum (sometimes here) used 50 pounds per 1,000 every week all summer. At first, before your soil has a high population of decomposing microbes, the organic fertilizer may become a little...sour smelling. That is ammonia gassing off. If you keep applying it the smell will become more of a composty smell, which is wonderful. That's when you know you have the soil good and healthy. The soy, corn, corn gluten, alfalfa and a few other grains are the raw materials in commercially bagged organic fertilizer. By buying the grains in unmarked, 50-pound bags at the feed store, you save about 5/6 of the cost of organic fertilizer. You can mix them or not. Doesn't seem to matter much. One thing I would not do is buy enough now for next year. It will get bugs in it and be pretty messy come March. I would still use it, bugs and all (they are organic), but know that it is a messy mess.

The organic approach to recovering from a fungal attack is to apply ordinary corn meal at 20+ pounds per 1,000 square feet. Corn meal attracts a predatory fungus that will take out the disease. If you grass goes all the way to dead, you still need to treat the area before you resod or else the new sod will never get started (voice of experience here). I really never had one speck of success with chemical fungicides, but corn meal almost always works for me.

Your weed is Mimosa strigillosa, mimosa vine.

dchall,

Is the 20 pounds per 1,000 sq feet of organic fertilizer for all grass types? Just wondering if that is an ok amount for centipede due to its low requirements. I am interested in trying organic next year. Alfalfa pellets are easy for me to get.
Thanks