Fire Blight is a bacterium that can attack more than 75 species of trees and shrubs including apple, pear, quince, mountain ash, crabapple, hawthorn, cotoneaster, and serviceberry. The bacterium over winters on infected plants in darkened, slightly sunken cankers. In the spring the bacteria are dispersed by insects, rain, wind, and animals.

Canker (where the bacterium overwinters)


Symptoms

  • Twigs, branches, and leaders on trees and shrubs wilt and blacken, especially during flowering.
  • Affected twigs and branches may bend over into the shape of a shepherd's hook
  • Blackened flower parts remain attached to the tree
  • Cream-colored liquid may ooze out of the cankers and run down the trunk and branches in the Spring. Usually it is very noticeable if conditions are wet.

Fire Blight on a Bradford Pear Tree

Shepard's Hook


 

Life History

The bacterium is carried from liquid oozing from the infected tissue to natural openings or wounds in susceptible plants by insects, rain, wind, birds, and various crawling insects. The leaves, and small wounds on succulent twigs and branches all can be sites of initial infection. Moist plant parts are blackened and killed. The bacteria then move farther into and girdle branches and the trunk. A slightly sunken, darkened canker forms in the invaded wood. Close examination will reveal a dark line at the edge of the canker. While plants are most susceptible during flowering and new shoot development, Fire Blight can continue to spread later in the season.


Favorable Conditions

  • Fertilizer applications create succulent growth. This increases the chance of fire blight
  • High temperatures (70 - 81 F), high relative humidity, and rainfall during flowering provide favorable conditions for Fire Blight development.
  • Injury due to hail or windblown soil opens tissue to infection.

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