The following is information on bacterial shoot blight, a disease now active in the landscape.
Bacterial Shoot Blight or Syringae blight is caused by a bacterium Pseudomonas syringae and its many pathovars. It can cause leaf spots, blights and cankers on susceptible hosts. This disease has been very active in the landscape on many hosts especially lilac, cherries, rose, apple, pear, willow, and photinia. Sometimes the damage on cherries and lilac can resemble fire blight on apple. On green twigs, lesions can appear as black streaks. On lilac, green shoots die, turn black and shrivel. Leaf spots are irregularly shaped, brown and often with yellow halos. Once the dieback dries out, the damaged stems can be pruned out. There are no effective chemical controls in the landscape. Applications of copper containing fungicides and streptomycin could reduce epiphytic populations of the bacteria in production nurseries during wet seasons, but for the homeowner it is probably best to wait it out and prune.
Symptoms of bacterial blight (Pseudomonas syringae) on leaves of a lilac. Photo by William Jacobi, Colorado State University, Bugwood.org.
Signs and symptoms of bacterial blight (Pseudomonas syringae) on a lilac. Photo by William Jacobi, Colorado State University, Bugwood.org.
Information from Bob Mulrooney, Extension Plant Pathologist, UD.