I have several of these in my zone 7, NC garden. I have had mine for over 7 years. This is a strong growing plant, the stems can get rather thick. It can get blackspot when it is stressed or blooming heavily, but it is very blackspot resistant. I haven't had any problem with mildew.
The heaviest blooming time is spring, but has some blooms all summer and fall. The blooms would credit a hybrid tea. Once they open fully, the blooms last only a short time (especially if there are heavy rains), but there is always another to take it's place. It has a wonderful scent. All in all, quite a delightful plant. --Vineyard Garden