I have treated this lawn for everything from brown to gray leaf spot, bugs and everything I can think of...my front yard is fine but my backyard.... Aweful! This particular decline has happened very rapidly and is just spreading. This WAS the thickest part of my lawn and now it is decimated. Anyone have any ideas? I've posted some picture of the area overall as well as the roots. Thanks for any guidance.

I don't know whether they like St Augustine, but fall Army Worms can cause that sort of destruction.

Thank you...you know, since you said that, I have noticed little dirt piles like something is burrowing, pop up in the same area. This preceded the dying.

I looked very closely in the grass and I found no insects. I even made several plugs looking, but nothing. Would I see those? Thanks again!

Have you looked into Take-All disease? Do you have any idea of your soil pH? Here are some pictures of Take-All:

https://www.google.ca/search?q...

Sod Webworm, or AKA Fall Webworm has been rampant in Kingwood TX killing entire lawns in 10 days or so. The stores can hardly keep the insecticide in stock. The clue is seeing small moths flying around in your lawn and beds. They lay eggs, then the moths eat the roots of your lawn. You can treat it with things like BugBGone, etc spray, but if you have a large infestation, you may have to resort to Cyonara spray. And then respray every week to 10 days as the cycle of hatching continues. Sad to say, if this is the case, your lawn will have to be replaced. Also if your neighbors aren't treating their lawn, you will have to retreat as I do every 2 weeks or 10 days.

Sod webworms eat the grass blades rather than the roots. You can check for them by putting two or three tablespoons of liquid dishwashing detergent into a 2 gall watering can and pouring some of the solution on a smallish area of grass, maybe two square feet. If they're there the caterpillars should come to the surface, give them at least five minutes to crawl out. The roots look dark in Susan's pictures which is why I thought of Take-All, but it certainly doesn't hurt to check for sod webworms.

We have Tropical Sod Webworms if that makes any difference? Many lawns have been affected here. It has been a battle for the past 2 months. My lawn is glowing with insecticide.

ShadyGreenThumb said:We have Tropical Sod Webworms if that makes any difference?

It doesn't make a difference, they still eat the grass blade not the roots according to this U of Florida page on Tropical sod webworm. Have you seen the caterpillars?

"......The first four larval stages (instars) are ‘window feeders’, i.e. they only feed on the upper surface of grass blades, and so the injury they cause is often overlooked. Fifth and sixth instars can severely damage grass by chewing entire sections off the leaf blade. Larval feeding occurs at night, and larvae hide in the thatch during the day. Caterpillars prefer dry and hot grass areas. Early damage is hard to notice and creates a ragged appearance, but as larvae grow, they consume considerable quantities of grass before pupating. Grass may recover if infestations are not too severe......"

http://entnemdept.ufl.edu/crea...

Edited to add this link from Texas Cooperative Extension which says the tropical sod webworm feeds on the leaves while they're still attached to the plant whereas the other sod webworms in Texas detach the leaf to eat it:

http://harris.agrilife.org/fil...

The Houston news is reporting the worst infestation of Sod Webworms in 30 years. I would treat for that no matter what but especially if you see moths flying around. I just ordered a bug light Zapper. Supposedly they catch a lot of the moths that way. If you have a brown patch of dead or dying grass, sod web worm would be my first diagnosis.

As I mentioned, the easy way to tell is pour some diluted liquid hand dishwashing detergent on a patch of grass and that will flush out the caterpillars. There are other moths that fly around on turf that aren't sod webworms so that's a useful way to verify.

Susan, if you're still with us, I just found this article from Texas A & M about this year's sod webworm outbreak that Cheryl mentioned. When I look at your picture some grass blades do look partly chewed but you also seem to have intact dead grass blades. It's possible to have more than one problem going on at the same time. But you mentioned having treated for bugs. Did you use something that would control caterpillars like sod webworms?

http://agrilife.org/harrishort...

I do think it would be a good idea to check for sod webworms with soapy water because it's better to be sure what the problem is. I remember when my late parents had a lawn problem and because their neighbour's and others' lawns nearby had been diagnosed by a lawn care company as having chinch bugs, they were going to apply an insecticide to theirs because the brown areas looked the same. When I visited and checked it out there were no chinch bugs, it was a fungal disease.

Good point, @sooby. This is also the time of year to use fungicides on Houston lawns. So if you treat for fungus and an insecticide that hits the sod webworm, she'd be right on it. The trouble with the sod webworms, is that we have had to reapply the insecticide weekly-10 days to keep at those #@$% generations that continue to hatch. These worms don't have a calendar. The chemicals are become less effective with each hatching generation. It needs to be reapplied. I am hoping by zapping some of the months that keeps them at bay. So far so good, no infestation by controlling the worms in my lawn. But it's glowing! But I am going to get the moths who lay eggs with The Zapper. I see literally 100's of moths fly out of the flower beds in the back yard. There is not lawn there, but I am sure they fly over my front lawn dropping eggs as they go.