A Technical Report from The Bartlett Tree Research Laboratories
Black canker and scab of willow (Salix) are two diseases that often occur together. The term willow blight is often used in reference to simultaneous infections. These diseases cause defoliation and twig dieback that can lead to tree death. Black canker and scab occur throughout the eastern and central US and in the Pacific Northwest.
Willow scab is caused by the fungus Venturia saliciperda. The fungus overwinters on dead twigs and infects succulent new growth in Spring. Leaves and twigs become less susceptible to infection when the growth hardens-off later in the growing season.
Black canker is caused by the fungus Glomerella miyabeana. This disease occurs later in the season and can cause cankers on twigs and branches. The pathogen overwinters as spores on dead twigs.