I just started mowing this lawn this year and the lady does her own fertilizer. When I saw these spots I knew she had to have just put down fert and got it heavy in spots but she claims they showed up before she put down the fert. I see these spots as well in areas that hold water but we haven't had rain in a couple weeks here. Is there anything else this could be? I'm leaning towards the lady just doesn't want to admit she put down too much fert.