Are the white spots on the leaves on the surface of the leaf or is a portion of the leaf being chewed away? There are a number of insects that scrape away the green chlorophyll part of rose foliage, but leave the veins intact. This can cause the plant to look like it has white spots on the leaves. Fortunately, it's fairly easy to control chewing insects with insecticidal sprays. If you prefer a low-toxicity approach, try using spinosad, a natural insecticide.