Fire blight (Erwinia amylovora) is a bacterial disease affecting pome fruits like apple, crabapple, pear, and quince. It usually enters the tree through flowers during bloom, but can also enter with injury such as from hail or pruning and affect any part of the tree.
The main disease symptom is the scorched appearance of affected twigs (Figure 1). Twigs wilt from the tip downward and form a hook like a shepherd’s crook (Figure 2). Leaves on the twigs turn brown or black but don’t drop from the tree. If left unchecked, symptoms will progress down branches, where cankers will form. Bacteria can overwinter in these cankers, and be transferred to flowers by insects the following spring, spreading the disease.
What to Do Now
While most fruit tree pruning is done during the late winter or early spring, when trees are dormant, you don’t want to wait to remove fire blight or it can continue to move into older wood, and eventually can even kill young trees.
During the growing season, when the weather is dry, prune back about 12 inches below visible symptoms. Remove the prunings from the yard/orchard and burn them. Between each pruning cut, clean your pruners by dipping them in a 70% ethyl or isopropyl alcohol solution for 30 seconds to avoid spreading the bacterium.
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