Disease name: Powdery mildews
Pathogen name: Several species of fungi
Hosts: Numerous species of plants. Hosts vary by the species of fungus.
Powdery mildews are caused by over 1,000 species of fungi that affect a wide variety of landscape plants. Most of these diseases grow only on the upper leaf surface and stems of plants, and do not invade the leaf tissue of the host plant. In most cases, powdery mildew is not a serious problem and prompt recognition and management can prevent severe damage to plants.
Some of the more susceptible trees and shrubs to exhibit powdery mildew symptoms include apple and crabapple (Malus), some cultivars of ninebark (Physocarpus), elm (Ulmus), rose (Rosa) and lilac (Syringa). Powdery mildews are also common on certain herbaceous plants, such as beebalm, phlox, and zinnias.