Can you tell what caused this problem?

Can you tell what caused this recent problem on a poa green?

If you guessed a disease such as rapid blight or anthracnose, you would be in the majority. But you would also unfortunately be wrong. Because the problem is a common, though frequently mis-diagnosed syndrome that we call localized black layer.

Black layer results from a lack of oxygen in the soil. It can occur over a large area, or it can occur in in localized spots or patches…