Yes, fungus on roses in the form of black spot or powdery mildew can be controlled with fungicide sprays, by increasing the air circulation (less crowding) and by good garden cleanup to remove infected leaves. Rosarians also use Neem oil, and mix up their own solutions  that usually contain baking soda to control the fungus. The easy way to grow roses without fungal infections is to grow disease resistant varieties. You local nursery or rose club will be the  best at suggesting disease resistant roses and also what type of fungicide products works best in your area. Keep growing, Marianne Binetti