Between now and August 15th is the time to apply your final nitrogen containing fertilizer to your roses. Application before the 15th gives the fertilizer time to work without encouraging new growth that will not have time to harden off before winter.
Got blackspot? Try spraying with a combination of Maneb (Manzate or Mancozeb also work) with tebuconazole (Bayer Advanced Disease Control for Roses, Flowers & Shrubs Concentrate). Not Bayer 3 in 1. Spray at 7 to 10 day intervals to avoid possible phytotoxic effects such shortening of internodes. Use only as directed!