I'd wager it's brown/large spot fungal infection. Look those up.

No one else is responding, so I am. However! I have no landscape experience, and I am fighting a similar issue in my own lawn. I will summarize here what I have READ about these fungal diseases, but suggest you investigate them further.

1) They are active in destroying grass in late spring and fall
2) Increased moisture increases fungal growth (all those rains you had, and never water more than once per week, probably less because St. Aug isn't very thirsty)
3) Fertilizer increases fungal growth
4) Sub-optimal growing conditions make grass more susceptible (get your soil tested, it's $25 for the best test around at Logan's Labs, then adjust pH and other soil minerals)

Most people combat the fungus with a chemical fungicide. Often two seemed to be used in alternating applications. Googling the grass and fungus name will give you lists of fungicides with the best effectiveness. Many of these can be very expensive, and they all seem to be toxic to some degree or other, so use them with caution.

Treat with fungicides, during periods of fungal growth (late spring, fall). Examine grass for disease (your observation that they pull out very easily indicates active disease).

Over the course of the next few years, fix your cultural practices (watering, soil pH, fertilizer, etc).

One other thing to try is cracked corn or corn meal across the entire lawn at around 10-20 pounds per thousand square feet. That'll help bring some trichoderma fungus into play, which is a hunter fungus that eats other fungi.

Do this about two weeks after you use the fungicide or it'll take the helpful fungi out too.

Morpheuspa, I'm currently dealing with three major large patch infections of my zoysia (7b, Durham NC). I was planning to be agressive with fungicide this year, because my number 1 priority right now is to restore the baseline health of the zoysia. Planning on alternating propiconazole / chlorothalonil with Disarm G on a two week basis at the end of August. However, I would like to attempt to replenish the soil once the disease pressure subsides.

What I always feel most uncertain about is timing. (When should I start? When should I stop?). I saw the recommendations for compost tea in my other thread, corn meal in general for trich, and for molasses for speeding up thatch decomposition (my zoysia drops a very thick thatch coat every year).

What would you recommend for timing to apply the organic, replenishment methods this fall?

Might want to research Companion or Serenade they are biological fungus preventers... Companion has shown some solid effectiveness in preventing Summer Patch (precollonizes roots I believe) - not sure how your fungus compares.

Would want to start putting it down ahead of similar conditions (temperatures or moisture) that first sparked your large patch issues.

+1 Boat. I'm always a fan of trying biologicals before pulling out the big guns. But if the biologicals fail, out come the big guns, of course!

For most replenishment methods, two weeks post the last application of fungicide is generally recommended. You may still catch the tail end residual of the fungicide, but with organic application that doesn't matter so much. Bacteria and fungi blow around in the wind.

Molasses will help thatch decomp (sorry I missed the thread, but I tend not to poke into southern lawn threads) somewhat, but combine that with some extra nitrogen in the form of soybean meal, Milorganite, or cottonseed meal and you'll accelerate decomp of thatch to much higher levels. Thatch has a lot of carbon and too little nitrogen to decay optimally. Molasses is a pure carbon that feeds bacteria very well, but doesn't bring any nitrogen to the mix. Soy, Milo, and cottonseed are all very high nitrogen.

I don't know how I missed the earlier post, or even if I missed the earlier post, but your problem is simple. Yes, you did start the disease problem by piling up leaves and leaving them thereby cutting off the flow of fresh air to the St Augustine. That will happen every time you do it - ask me how I know.

No, you do not need to dig it up and put in new sod. If you do that you will have dead new sod in two weeks - ask me how I know.

No you do not need to apply a chemical fungicide. It is already too hot in Texas to use chemical fungicides - ask me how I know.

The answer to the problem is to apply ordinary corn meal or cracked corn at a rate of 20 pounds per 1,000 square feet. And again, ask me how I know. I have used corn meal every year for the past 13 to get rid of diseased spots created by "someone" who won't stop leaving garden clippings on the grass. It takes 3 full weeks to see the improvement. Since this is your first time, you might want to repeat the corn meal in a month just to be sure you got it all. And do do the entire lawn. Corn meal is an organic fertilizer. If you only use it on the diseased spots you'll end up with dark green spots instead of yellow/brown spots. After a month it should start coming back and looking like this...

There should be no brown, tan, or black spots anywhere on the plants.

It just needs to stop raining! My St Augustine is just full of yellow spots from too much rain. It's a resilient grass and will recover with the cornmeal and less rain. I saw on the news today that we (DFW area) has had 16+ inches of rain this month and another storm coming tonight.

Your good spots look pretty healthy, it will be okay just to toss out the cornmeal (wait until the end of the weekend) and give it time to recover. Every time I fail to move objects from the lawn, the grass suffers and sulks. It does recover though.

Patience Grasshopper :-)

So much rain...

Cornmeal is the "immediate control" for many lawn diseases. With all your rain (mine too) I would apply it monthly for the rest of the season. I need to hit my Floratam. It is still growing but it has spots on it.

Observation runs rather counter to his supposition. Also, I want to see his field study that shows no effect from adding corn meal...except that there isn't one.

gotsqueeze, you really know how to get my blood pressure up. As it turns out, the effectiveness of corn meal as an antifungal agent is entirely the reason I started using organic fertilizer and for everything else. It has been extraordinarily effective and repeatable in my yard every year since 2002. After about April in Texas, there are no alternatives but to use something organic. The chemical fungicides all burn or become ineffective above 85 degrees.

Linda Chalker-Scott is a well educated troll. Dr Jerry Parsons is practically a shill for the agri chemical industry at Texas A&M. Together they can scare anyone out of doing what works.

It does. I wasn't going to bring up my personal opinion on either of them, or their funding sources. David covered that quite nicely, except I probably would have omitted the word "practically" from "practically a shill."

dchall, what fungus's are active in those high temps? Reading about the brown / large patch diseases of warm season grasses, it seems like they are most active in late spring / fall. I know they have a minimum soil temperature to be active. Do they go inactive in summer because of the heat, or because there's less 24-hour moisture during the mid summer?

just curious.... what makes it to late to plant seed? The heat?? At what point would u say is to late??

thanks for any advice !!

Yes, the heat. But in your case I lost track of what was going on. You're talking about bermuda seed and I was thinking northern grasses. So...never mind. Sorry! Bermuda needs warm soil to germinate. Now would be fine to seed. How is the lawn looking after a few weeks? What did you do and how does it look?