I have problems with my roses. They have brown spots and roses don't get big anymore. I put food for roses but it doesn't help.
It sounds like you may have some fungus problems getting at the foliage. I recommend spraying the roses with a good fungicide such as Green Cure. It is an Earth Friendly product that works very well, I have used it for several years now. It is available from the Planet Natural website. Also here are some links to articles that will be helpful to you:
I have found that watering the rosebushes with some water that has a product called Super Thrive and a good root stimulator both mixed into the water helps stimulate them. This mix helps them deal with many types of stress that the rosebushes may be dealing with. Water the rosebushes with such a mix the next 4 to 5 times they need watering.