I tired getting a response over in the Commercial Lawn Mowing section, but apparently there is too much traffic to get noticed. I'm just looking to see what this might be. I haven't been back by to see if it is still there, but even still, for future reference, it would be helpful. Well, I use the term grass loosely. I have a customer that has a backyard full of crabgrass. I know in Florida that might be a good thing, but here, that's a nightmare. The first cut, the grass was roughly 2-3 feet high and I double charged (could have triple or quadruple charged but they signed up as a full time customer). Anyways, By the time I was done, the whole back yard was one big clump, so blowing it around wouldn't have done much good. I went back today to run through it again and try to scalp the whole thing (he wants it all gone) and they reported a black/purple fuzz growing on some of the grass. I assumed it was just mold on some of the clumps, but it turns out, some of the grass was actually growing this stuff and even after mowing and dropping it down to less than 2", some of the spots are still showing this stuff. I would have gotten a picture, but I didn't have my camera. Any ideas on what it might be and what I need to do to get rid of it. They seemed concerned as they have a small child and a dog that frequently uses the backyard.