Fire blight is one of the most destructive diseases of apple and pear trees. In Calgary, mountain ash, hawthorn and cotoneaster are also affected by blight. The bacteria can kill flowers, twigs and branches, and sometimes whole trees and shrubs. Mountain ash trees are badly affected by bacteria in Calgary and surrounding areas.
In spring, branch and trunk canker symptoms can appear as soon as trees begin active growth. The first sign is watery, light tan bacterial ooze that exudes from on branches, twigs, or trunks. The ooze turns dark after exposure to air, leaving streaks on branches or trunks.