Better pics of spots, I'm thinking maybe Helminthum:

That's just weird. Bermuda rarely gets a disease.

I would apply ordinary corn meal at a rate of 20 pounds per 1,000 square feet. Using the sprayer on your hose just wash it down to the soil and let it go. In 3 weeks you should see improvement. I would tend to continue using corn meal once a month for the rest of this growing season. You might get a little aroma of sour milk after the first app, but that will go away with the rest of them. You can get corn meal in 50 pound bags at your local feed store. Call first to see that they have it in stock.

It's good old fashioned black leaf spot brought on by the thatch layer in that area. The stems are having to stretch too high to get past it & causing the weird looking weak top growth. Excess OM (thatch) is being attacked by any number of fungi, but the spots on the grass are just a symptom, they won't do much harm. Manually dethatch that area with a rake until you get some bare dirt. The Bermuda will spread to any bare dirt you make available, but will only grow straight up in thatch.

Thanks for your input. Do you suggest dethatching now, in the fall, or waiting until spring?

I'm doing a Logan Labs test next summer, the last two I've been using the local extension. In that area of the lawn I have 1-4 inches of nice brown soil (what I get tested), and then a sharp division into red clay. It's not at the surface, but it's not far down, and the dividing line is stark. You can literally make a pot out of it. When it's wet it comes out in huge, softball size clumps when I dig with the shovel, big soft plastic sticky clay. When its dry, it's nearly impossible to dig in, it's more excavating a hole in terra cotta by slowly scraping away the sides. Dry you can't dig a shovel in for love or money.

Yes, I would like to level the lawn. Right now I have a 2 year old and a new baby so I'm trying to stick to smaller projects.

I've been wondering about the disease as well. That soil there is almost always quite dry, at least at the surface. There is no puddling once the rain stops - it's on a grade. Now that the grass is so thin the topsoil layer is getting "grainy" and dusty and I'm worried about it being eroded away.

Weeds also do not grow well there. I have an ongoing oxalis infestation in the yard, and they have a hard time growing in that spot. They will live there, but they won't flourish like elsewhere, they get dry and brittle. Other weeds don't really bother colonizing the location.

I'd like to figure out if it has any other cultural problems beyond losing water to the trees / downhill. If you have any other suggestions or cultural questions, please let me know! Here are the last two state lab tests I've had done on the lawn. Samples were taken from the whole lawn, though next year I may submit some from just in that location.

Organic matter is low. I mulch mow and mow in whatever (not many) leaves fall. I did a bag of Milorganite this year, and 25 lbs of cracked corn / 1000. I'll throw a few organic feedings at it next year as well.

To clarify, I did not recommend dethatching your yard--I said use a rake to pull the dead crap out of that particular spot. This is not a guess, I'm looking at that thatch & it's way too much. The stolons are growing over top of dead stuff when they should be laying flat on bare soil or invisible. I have a spot like that too & it collects clippings for whatever reason, so I have to rake it out every few months. At my place, the rest of the yard has a very healthy, appropriately thin, dark thatch layer, but that 1 spot just gets it too thick, so it looks like straw & lifts the new growth up off the dirt surface. Definitely get that soil test done when you can also & DC is right, mow it lower if you want it healthier.

I just snapped a pic of this bare shady corner so you can see the way the stolons should spread along the bare ground. In your pics, they can't reach dirt & simply grow up to get above that layer, but get