It could be some form of fungal disease or a female dog urinating on the lawn. If it is a fungal disorder then treating it with a lawn fungicide is in order. To prevent dog urine from burning, soak the spot down right after the dog pees with two or three gallons of water to dilute the urine. When things cool off in mid to late August, you should feed the lawn. Don’t feed during the hottest days of summer.