Powdery mildew is the most common fungal complaint suffered by roses. The fungus Sphaerotheca pannosa is visible on both the upper and lower leaf surfaces, on buds, and on new growth. Infections can be so mild that the only effect is a slight folding of the leaflets. On other roses, the infection can be so severe that the plant and all its blooms are disfigured. See the University of California UC IPM Online Pest Note for more information. See the Photos tab.