These spots usually enlarge and coalesce, often causing leaves to become misshapened. Eventually leaves may be killed. When the infection spreads around a twig, it becomes girdled and dies. This phase of the disease is evident as young new shoots develop in the spring. Shoots turn a black color, droop over, and die.
Control consists of pruning out blighted twigs as soon as they occur.
Cut several inches below the margin between healthy and diseased tissue. Prune in dry weather only, and be sure to remove and destroy all infected tissue. Where possible, thin plants to provide good air circulation. The use of a copper-based product such as Bordeaux mixture may aid in disease control. Applications should be started when new growth appears in the spring.