(Pseudomonas syringae pv syringae)
Damage: Symptoms appear from bud break to bloom. Brownish-black discoloration appears on one-year-old stems, often near branch tips. Buds and flower clusters within or adjacent to the infected stem turn brown and die. There is a distinct margin between diseased and healthy tissue on the stem.
Disease cycle: This bacterial disease is very common and spreads under cool, wet weather in the spring and fall. It often becomes severe on plants that have been damaged by frost.