Really hard to say. Could be simply slow coming out of dormancy. Could be a fungus although it is not obviously a fungus as would be indicated by circular designs. It could be a dog pees there every day. It could also be that someone laid yard clippings in that spot for longer than a day. St Aug is very susceptible to fungus when air circulation is cut off. I used to get disease spots every year until I figured out my wife was laying yard clippings down here and there. Do any of these other possibilities ring a bell?

Are you mowing at your mower's highest setting? If not, fix that. Secondly, have you mowed at least twice this year? If not then forget about fertilizer. The roots are not ready for fertilizer. Thirdly, once the grass comes out of dormancy, it comes out with a vengeance which requires no fertilizer. I would wait until you see the growth backing off and then fertilize in preparation for summer. Fourthly, are you watering no more than twice a month at this point in the year? Soggy soil is not good for grass.

Or if you want to use organic fertilizer, you can do that any time. They do affect growth but they really help the soil much more than you know.

Thanks, dchall...
Here are some answers. The grass had come out of dormancy in the area photographed, and then blades started yellowing in the areas you can see in the photo.
I put down fungicide, but this doesn't have the normal pattern I've seen with fungicide like you said - not circular. Also, it's gotten worse since I applied fungicide.
No yard clippings were laid in these areas. Last year the really bald patch had a bad case of brown patch fungus, so I'm not surprised that spot is slow to come back.

Regarding dogs - we do have one, but we generally keep an eye on her elimination habits and wash down the spot with water. I don't think this is her fault - maybe one or two spots but she mostly goes in the back yard, and again we water that down after she goes.
We have not needed to turn the sprinklers on in the last few weeks due to lots of rain.
The yard is ready for it's second mowing now.

This morning from up on our deck I can see similar spots in the backyard. The fact that we found lots of wireworms back there a few months ago and I found one wireworm in a test dig in the front yard yesterday has me thinking insects.

It just doesn't look like the patterns of fungus we've had in the past, and we've had lots of fungus to deal with.
And there is too much of it to be the dog in my opinion.

Thanks again.

St Augustine? Could be just something underneath that is feeding on the roots. Grubs or other vermin that finds roots of grass appealing. Why not measure out a small section and dig down to see if there is any sign of this.

If not, then it could be any number of things that might have come to the area---and left.
Maybe spread a little compost over the area to invite re-growth.

Just a thought.....you don't have a dog do you which might have used that particular area to do doo doo.
Urine can do what is pictured if he doesn't pick on a definite spot.
It might just fill in naturally given some fertilizer......but compost is better.

Hi Goren... In the original post I noted the discovery of one wireworm, which do feed on the roots. I only found one in the small square foot area I dug up in the front, but we did find a lot more in the back yard earlier this year.

I still don't think it is the dog responsible for all of this, but it does look similar to dog urine burn.

I wish I could just ask the grass and have it tell me. ;)

Thanks for responding.

I can see you are convinced you have a bug problem. Furthermore you believe it to be wireworms because you have evidence. Since all the other possibilities have been eliminated, it must be. But I'll tell you - in all the years on this forum I had to look up wireworms because nobody has posted about them before. Going with that assumption, it appears wireworms have the unusual ability to recover from normal insecticides. With that in mind I would suggest trying beneficial nematodes. These critters enter the host insect bringing a disease. They lay eggs inside the dying host and feed on it when they eggs hatch. The only catch is the soil must be pretty moist when you apply them. I usually tell people to apply on day 3 of a 4-day rainstorm. Beneficial nematodes need a film of water to move around on. Apply to dry soil and you wasted your money.

I would say, though, that if your picture is recent, it is not ready for even a first mowing. You are mowing too low. Unless you have a dwarf variety (and yours doesn't look like it) St Aug is always mowed at the mower's highest setting. You are asking for any number of problems if you mow it short like that.

Thanks, dchall. In reading up on wireworms, I see that they are hard to beat with typical pesticides. Several posts/sites recommended ensuring that the pH is right in the soil so that you have happy grass that can withstand their presence. I still don't know if they are the "root" cause (pun intended). I do have a soil test from the local extension office, so I will follow their recommendations regarding fertilization. No lime was recommended, but phosphorus was excessive in the soil, so I will keep that in mind.

Regarding mowing, this is what they recommend (I know we have put down Palmetto sod in several areas, but who knows what the original was): "St. Augustine grass performs best when mowed between 2 and 4 inches depending on the cultivar. The normal growth cultivars like Raleigh should be mowed between 3 and 4 inches, while the semi-dwarf growth habit cultivars such as Palmetto and Mercedes can be mowed between 2 and 3 inches. Begin mowing as soon as the lawn turns green in spring. Always leave the clippings on the lawn in a practice called 'grass-cycling'. If prolonged rain or other factors prevent frequent mowing and clippings begin to clump, they can be collected and used as mulch. Never remove more than ��" of the leaf tissue in any single mowing. For more information on mowing lawns refer to HGIC 1205, Mowing Lawns."

Oh, they recommended lime in the backyard in early spring, so we have applied that.

I'll wait until next weekend to see if we're ready for mowing.

I'll update this post as things progress one way or the other.

Thanks!

Oh, and thank you, dchall, for the information regarding nematodes. I'll check into that.

Regards.

An update - the spots of dead grass seem to be filling back in now. Still not 100% sure what the root cause is.