Having a problem with this in Zoysia. Whatever this is, it has appeared in only one section of turf on the property. It seems to be more present in the areas that are in the path of drainage from storm water. It does not appear to be harming the turf, as the grass is trying to grow up through it. But it does seem to be smothering the turf to some degree. It is a crusty material that feels much like plastic. When you pull some of it up, underneath there is a white fuzzy material that resembles mold. When you step on it, it feels rubbery.