Rust Fungus On Rose

This appears to be a fungal disease called Rose Rust; its very common on roses. If you look at the underside of the affected leaves and you see orange colored fungal structures (sometimes dark brown and black structures appear when the fungus is in the reproductive stage) – it does look like rust. This fungus is spread by water, so splashing water will move it upward thru the plant. It is also favored by shade and poor air circulation. You may need to consider a fungicide if its a very bad infection, but you can reduce the spread of the spores by removing the affected leaves (without defoliating the shrub), pick the fallen leaves up and dispose of them in the trash, prune for good air circulation around/within the shrub, and grow roses in full sun. Here’s more info about Rusts and Roses: http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/DISEASES/rusts.html
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7465.html