It sounds like Take-all-Root-Rot from what you explained about the short black roots. Cut out a 1x2 foot section of the affected area and take it to your local extension office to have them examine it/determine what it is.

This disease is primarily observed during the summer and early fall months. By the time the leaf symptoms appear, the pathogen has been active on the roots for at least 2-3 weeks, probably longer. Any stress placed on the grass will encourage or worsen the disease.

This disease is very difficult to control once the above ground symptoms are observed. Therefore, measures that prevent or alleviate stress are the best methods for completely controlling the disease or at least decreasing the potential damage.

Because the roots are affected, they will not be able to efficiently obtain water or nutrients from the soil, nor will they be able to store the products from photosynthesis.

Here are a few things to do NOW.

1. Frequent foliar (leaf) feeding of all nutrients (N, P, K and micronutrients) in small amounts will be necessary. The roots are not functioning properly, and so will not be able to efficiently obtain nutrients from the soil. Spray Soluable Seaweed powder weekly with a pump sprayer/fine mist until the leafs are wet. Spray in the early morning or late evening. Use molasses as a wetting agent.

2. Extra potassium is useful in late summer and early fall. Use Sulfate of Potash if staying organic. Apply immediately @ 2-lbs. per 1000sqft.

Do not apply lime or herbicides.

Raise the mowing height to the highest recommended height/slightly higher until conditions improve. Mow as frequently as necessary so that only one third (1/3) of the leaf tissue is removed.

Thanks for the input. This may be a dumb question in this forum, but where does one buy water soluable seaweed powder, Sulfate of Potash and what's up with the molasses? I have access to a couple of seed and feed places, but I'm hesitant to go in and ask for seaweed powder.

Powdered seaweed might be harder to find than liquid seaweed (already wetted) at garden shops. If you really want dry seaweed look in an Asian market. It comes by the brick.

I don't like sulfated anything, even if it is recognized as organic. Having said that you can usually find sulfate of potash (potassium sulfate) in a real garden shop (not necessarily at HD or Lowe's).

Molasses is a great source of available carbohydrates for the soil microbes. They thrive on it like we do. If you want to multiply the microbes in the soil, spray with molasses. Molasses also makes a pretty good wetting agent if you want something to stick to the leaves of a plant. I believe that was what scoot kat was suggesting.

Other suggestions include hitting it again with 20 pounds per 1,000 square feet of ordinary corn meal; and spraying with milk at 3 ounces per gallon per 1,000 square feet.