I've been doing this for quite a while now and I've got to ask this question cause I don't have an explanation for it yet. Yesterday I was mowing one of my properties that I do every 2 weeks.........centipede and zoysia lawn. Last time I was there most all of it was nice and green with the exception of one area that the sprinklers were not hitting. Inside a fenced area there is a nice area which is zoysia. When I cut it 2 weeks ago it was also green and growing nicely.............yesterday I get there and areas of it......especially my old tire tracks..........were grey and looks burnt! Luckily the lady either hasn't seen it or isn't as picky as I think she is. I can't understand this.......It isn't dull blades and I didn't take too much off.......the stuff barely grows between mowings. If I had to describe it I would say it looks like I have run through a chemical that was applied to the lawn for centipede and then tracked it onto the zoysia but the zoysia didn't appreciate it. The centipede was untouched, no burn marks or greying, but that wasn't the case for the zoysia. I've noticed this in Bermuda as well.........some yards be grey when I return to mow them after a week.........usually where the tires ran over it. It can't be my mower because I use different mowers for different applications and on the bermuda a homeowner had it happen to him as well. I'm a little puzzled here ...........this just a me thing or does it happen to anyone else?