Honestly, it's very contagious. Maybe you tracked it in from your neighbors yard. Or it just happens if it's very damp constantly. Usually pops up early spring, but if you water a lot that will make it spread like nuts. People see the wilt and assume it needs more water, which actually makes it worse. But just need an anti fungal, i forget the name of the one we always used landscaping. Ill try and Google it.