I have a customer with some spots in his yard. Great looking yard, I am thinking it may be brown patch. The spots are up to 6" in diameter as the largest and then they get smaller from there. There are just a couple in the front yard and the back has much more just beyond the driveway and near the back patio. They don't have any green grass in the center, just bleached white dead grass... They don't look like it would be something from a mower as they are not wide spread throughout the lawn and they don't seem to follow any pattern that I can think of. They are perfect circles for the most part. I will attempt to have some pictures taken and posted asap. NPP to wipe it out and then the bermuda should fill back in?