Yes, I recognize this is an old post, but for the benefit of others landing on this page... I'm 99% sure this is Creeping Beggarweed or Spanish Clover (D. incanum/D. laxiflorum). Mine produce a deep pink, almost purple flower. I spent an exhaustive afternoon in my back yard digging a ~6' x 6' patch of it out of my St. Augustine about 2 yrs. ago. I would compare the underground root system to that of Torpedo grass... invasive and virtually impossible to eradicate. My temporary joy of digging out the mother lode tap root (at least 10" deep!) was quashed when sprigs of it started popping up again. As the natural/organic method failed, I got some Roundup. The grass has almost fully recovered now; I get an occasional sprig though. Then I noticed it was invading a stretch of front yard near the street. Mother Nature sent Irma to help me with that area. Put the debris pile on top of it and by the time it was picked up, mostly everything was dead underneath. It made it easy to pull most of the roots out then. So for the sprigs that have survived both there and in back, I take a can with both ends cut off, slip the weed inside of it (Beggarweed and/or Torpedo), and try to protect the surrounding St. Augustine as I spray the Roundup. My condolences to anyone battling this... good luck!

If you had not already applied a chemical fungicide I could have helped you. Recheck the label on your fungicide to be sure it works in the temperatures you are getting now. Most tell you to not use above 80 or 85 degrees F. If that's on your label then stop using it now. The easy solution to the problem, had you not already used the chemical, is to apply ordinary corn meal at rate of 20 pounds per 1,000 square feet. If you cannot find corn meal in 50 pound bags at your local feed store, you can also use cracked corn or corn flour from the grocery store. You can find it in 25 pound bags in stores that cater to the Hispanic community. Corn meal works by attracting a beneficial predatory fungus which kills the disease fungus. So if you have already used a fungicide, then the beneficial fungus is gone. If the temps are too high for your chemical fungicide, then wait 2 months and try the corn meal. Or you might be able to speed up the recovery by using compost at a rate of 1 cubic yard per 1,000 square feet along with the corn meal. Compost contains the beneficial fungus you need and will reinoculate the soil with it. Here are before and after pictures using corn meal. The grass in the pictures were in deep filtered shade of a large live oak tree. That was about as dense as it ever got in that area with zero hours of direct sunlight. St Augustine does not get thatch except under the most ridiculous maintenance practices. It would require daily watering and weekly fertilizing with a liquid spray. I have seen it, but only on one yard. And as soon as the management on that yard went back to normal the thatch disappeared. That lawn was growing entirely on top of the soil. Aerating won't help. Would you characterize your soil as sand or something else? Okay I just read back. This is Floratam? Floratam is the most disease resistant variety of St Aug. It is also the most sensitive to chemicals. Stop mowing it low and let it grow up for several weeks until it is higher than your mower's highest setting. Then mow every 2-3 weeks. The idea is to grow deeper roots which can get nutrition from deeper down in the soil/sand. You should see the new Floratam growing in at a faster rate than the disease can progress. You MIGHT still need corn meal to get rid of it, but tall Floratam in full sun can outrun a disease. Deeper rooted Floratam needs much less water and even less fertilizer. I have grown it up to 32 inches high in the Texas heat and drought, and it never needed either irrigation or fertilizer over a 2 year period. I'm not suggesting you do that, but the grass loves being tall. Here are some other tips to keep disease out of your lawn. Never put anything on the grass and leave it overnight. No toys, no yard clippings, no trash, no yard tools, nuthin that would cut off the airflow overnight. Disease will form in the morning dew if the dew cannot evaporate easily. Also be sure your soil drains well both downward and outward so it never puddles anywhere. You can improve downward percolation by spraying the entire yard with any clear shampoo at a rate of 3 ounces per 1,000 square feet and follow that up with 1/2 to 1 inch of irrigation or rain. And one last question: what is your watering regimen? How often and for how long do you water when it is not raining?

Since the Bermuda is growing above the St. Augustine, you can wick 'Roundup' on the Bermuda leaves without effecting the desirable turf below. Put some Roundup in a dish, get some on your fingers without dripping, and rub the Bermuda leaves until completely wet. You may have to repeat this a few times over the period of a year , before getting a complete kill.

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