These spots may enlarge and coalesce, causing leaves to become misshapen. Eventually leaves may be killed. When the infection spreads around a twig, the twig becomes girdled and dies. Shoots turn a black color, droop over, and die. This phase of the disease is evident as young shoots develop in the spring.
Control consists of pruning out blighted twigs as soon as they occur.
Pruning cuts should be made several inches below the margin between healthy and diseased tissue. Also, thin plants to provide good air circulation. Prepared by Paula Flynn , Department of Plant Pathology Iowa State University , Ames, Iowa. This information subject to a usage policy .