Fireblight

Fireblight, or fire blight, is a bacterial disease that frequently attacks trees in the pome family. This includes pears, quince, crabapple and my apple tree! Fireblight can also attack raspberries and blackberries, so you know I don’t like it!

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Note crook-shaped tip (top) and progressively less diseased areas inside the apple twig. (Kate Russell)

The Erwinia amylovora bacterium is the cause of fireblight, but you’ll never see it without a microscope. The most common first sign of infection is the die-off of an entire twig. The dead leaves hold fast to the stem throughout the growing season as the infection spreads.


Fireblight can be fatal to your fruit trees and it is difficult to manage. Carefully monitoring your trees when they flower can provide early warning. Fireblight normally attacks through the blossoms, carried in by bees and other insects from other infected trees. As blossoms become infected, they wilt and turn dark brown. The infection then spreads down the twig. Very often, the tip of the diseased twig will curl into a shepherd’s crook shape.


Insects pick up the bacteria from small, insignificant looking cankers that become active in spring. These cankers are actually dead tissue from the previous year’s infection. A clear, tan ooze can be seen dripping from these cankers. Each droplet can contain millions of bacteria which are then spread by insects and droplets of water. Infestation can be prevented with applications of Bordeaux mixture in fall and winter.


Once identified, the only treatment is removal of the diseased tissue. Cuts should be made 8-12” below the infected area and clippers should be sanitized after each cut with a household cleaner, such as Lysol,  to prevent further spread. The infection can be seen by scraping off the bark and cambium layer to expose pink to orangish-red streaks. It is critical that all of the infected tissue is removed or the disease will continue to spread.