I need help with this one. In 11 years of lawn care I have never seen this kind of devastation. Customer has been with me for 3 years. I treat (Fert/weed/insect/Disease) 2 adjacent properties and last treated these lawns 2-1/2 weeks ago. During my last visit lawn was Lush and Green. Customer called 2 nights ago and said his front lawn was dying.... I immediately drove to property and expected to see some small patches of summer disease and stress but was stunned to see that a large portion of the front lawn was "yellow". The devastation was more advanced toward the street end of the yard and as you moved back toward the house the pattern of yellow grass was clearly limited to the Tire marks of the mower. ( customer uses a mowing service). I could see no clear connection to any lawn disease. The back yard is more shady and had no evidence of damage, further the neighbors lawns I treat were fine as well. Is it possible that the mower was contaminated with some kind of non selective herbicide? The discoloration looks just like someone sprayed lawn with round up. This would explain the speed of the kill. Otherwise I am at a total loss for an explanation. The front lawn is in full sun and the customer (against my advice) over-waters the lawn. HELP.