Dutch Elm disease. Photo by: William M. Brown Jr., Bugwood.org

Vascular staining by fungus. Photo by: Paul H. Peacher, USDA Forest Service, Bugwood.org.

Powdery mildew on roses. Photo by Bob Mulrooney, Plant Pathologist, University of Delaware.

Powdery Mildew on common lilac. Photo by: Whitney Cranshaw, Colorado State University, Bugwood.org.

Frog-eye leaf spot on red maple. Photo by Bob Mulrooney, Plant Pathologist, University of Delaware.