new hedges put in last year....don't know if they are Amur or other type...fast growing ...shiny dark leaves....now have many leaves turning gray white and stiff and very leathery but not turning yellow or dropping off..... first noticed it in my neighbors hedges....seems to be working it's way down the row on theirs and now starting on ours..... humid this year, rain amounts normal.....fertilized hedges with Osmocote twice and watered occasionally . all hedges are planted in full sun and mulched ......powdery mildew ? treatment ?