Fire Blight

Fire blight is a bacterial disease that frequently attacks trees in the pome family. Pomes include apples, pears, quince, and crabapple. Fire blight can also strike raspberries and blackberries.

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

The Erwinia amylovora bacterium is the cause of fire blight, 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.

Fire blight can be fatal to fruit trees and is difficult to manage. Carefully monitoring your trees when they flower can provide early warning. Fire blight enters through the blossoms, carried in by bees and other pollinators from neighboring 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 dead tissue from the previous year’s infection. A clear, tan ooze may drip from these cankers. Each droplet can contain millions of bacteria. Prevent fire blight by applying a Bordeaux mixture in the fall and winter.

Inspect suspect twigs by scraping off the bark and cambium layer to see if pink or orangish-red streaks are visible. Once identified, the only treatment is the removal of the diseased tissue. The cut should be 8-12” below the infected area. Be sure to sanitize the pruners with a household cleaner after each cut to prevent infecting healthy tissue.