Infected tissues may exude either small droplets of a milky-white ooze or fine, hairlike strands containing millions of fire blight bacteria that can initiate new infections. The ooze, which later turns an amber color, contains countless bacteria that also are capable of causing new infections. Shoot blight is recognized by the rapid dieback of shoots. Infections begin in the shoot tips and move rapidly down from one to twelve inches a day. Newly infected tissue becomes water-soaked and dark green or reddish brown in color.
Hawthorn leaves turn yellow, then brown, shrivel, and fall prematurely.
The infection may continue down a shoot or flower spur into a larger branch or trunk, forming a canker. These cankers continue to enlarge during the growing season and may girdle the affected part, resulting in the death of the entire branch or tree. The surface of a canker is somewhat sunken, relative to the surrounding healthy tissue, and the bark is usually darker in color. In some cultivars, it is difficult to determine the margin of the canker without cutting into the wood to expose the discolored and infected tissue. The diseased inner bark of older branches becomes reddish brown and marbled, in contrast with the whitish color of normal wood.