Symptoms - White powder coats leaves, shoot tips and flowers in summer. Sometimes confused with downy mildew. Powdery mildew also often is accompanied by stunted and distorted growth, and reduced flowering. Sometimes a pale beige felt appears on the undersides leaves with a yellow area above, or affected foliage can appear black or discoloured.
On roses, white powdery deposits appear on flower buds and on leaves in spring. The disease overwinters on fallen leaves or as infections on young stems and in buds. In spring the spores re-infect young leaves. This disease can also spread by wind and can re-infect even at low humidity.
Like rose rust, this fungus can only grow on living host tissue.