"According to author and horticultural professor Jeff Gillman, who has conducted extensive research on blackspot remedies, a spray composed of one part milk and two parts water is the best answer to the disease. He says this simple solution, if applied weekly, will control blackspot as well as any synthetic fungicide, including Chlorotalonil."
Black spots on the leaves of your rose bushes, followed by yellow leaves and then bony stems and no leaves? Pull off leaves with black spot. Mix 1/4 cup of skim milk in a gallon of water in your watering can and rinse over the rose bushes, the rose bush will sprout many new growth stalks since it responds to milk just like a good fertilizer. I would repeat this rinse every 4 weeks.