I have had two customers so far with this problem and it seems to be more and more an issue. There is a black mold that grows on the soil surface under the grass, not on the grass, in areas that seem a little more damp and thinner maybe due to shade. Bermuda lawns. It seems to be a side problem to the thinning grass as the grass is thin so it then allows the mold to grow. Two questions, what is it? and How do I get rid of it and not have it come back. I believe one cause is the areas being more damp. I believe I stopped it in one area but not sure what stopped it as I threw some organics and synthetics at it trying to get it to stop. SO, any help would be appreciated. I believe I took pics of it in a earlier thread.