Hello, i have a line of "showtime" red hedge roses that have developed a problem the last couple years after their first bloom. The leaves start to die from the outside in and fall off, new growth is also slow and underdeveloped. I fed them in April and just fed them again. Any Ideas? Thanks.

Could you please take some close up photos. You could include some of the leaves with the darkened areas. Maybe a photo or two of the back of the leafs and some of the whitish areas.