During wet weather, a milky-like, sticky liquid containing bacteria can be seen on the stems and branches. Pruning cuts should be made 12 to 18 inches below any sign of infected tissue. Disinfect all pruning tools between each cut, using a solution of 1 part household bleach to 9 parts water. Succulent new growth is easily infected, if injured by insects, hail or wind. Avoid high nitrogen fertilization, which increases succulent growth.
Chemical control is difficult.
For crabapple trees, use either streptomycin, copper hydroxide or basic copper sulfate. Apply all chemicals according to directions on the label. More information about fire blight is available in HGIC 2208, Fire Blight of Fruit Trees. This disease is caused by the fungi Sphaerotheca species or Podosphaera species and is most prevalent during dry, hot periods. The fungus causes gray-white powdery patches on leaves and new shoots.