I have several light green patches that are 3-5 ft in diameter in my own lawn. When I pull on the grass, I can pull up a "mat" of grass. (The roots are no longer attached to the soil.) These patches have spread. I heard that the whole lawn would eventually be killed off if it weren't treated. I haven't dug into it yet to look for grubs as I see know skunk or crow damage. Is it a fungus or disease? I would appreciate any help.