Apple tree with fire blight

Symptoms of Fire Blight

What are the symptoms of fire blight?

How is it diagnosed? Part 2 of our series on this serious fruit tree disease – see Part 1 here.

Begin watching for fireblight infections in early spring during periods of wet weather. This is when the bacteria begin to produce ooze. Visual symptoms first appear on the flowers and then progress down the branch.
Infected blossoms appear water-soaked and wilt rapidly before turning dark brown; this phase of the disease is referred to as blossom blight. As the bacterial invasion progresses, leaves wilt, darken and remain attached to the tree (see right); this gives the tree a fire-scorched appearance, thus the name “fire blight.”
Infected twigs darken, and branch tips may bend over, forming a “shepherd’s crook.”

image of shepherd's crook branch deformity caused by fire blight disease - symptoms of fire blight
shepherd’s crook branch deformity, symptomatic of fire blight disease

During wet conditions infected tissue may exude creamy bacterial ooze in droplets or fine, hair-like strands. Infected fruits also exude bacterial ooze.

Rather than dropping from the tree, infected fruits gradually dry and remain attached to the branch.

Fire blight cankers on branches or stems appear as dark discolored areas that are slightly sunken, with a narrow callus ridge along the outer edge. The narrow callus ridge is diagnostic for differentiating fire blight cankers from fungal cankers. Under the bark associated with a canker, the inner bark turns from green to brown, but the appearance varies depending on plant variety. Droplets of bacterial ooze may appear on the canker.

A certified arborist will diagnose your tree according to the appearance of symptoms and suggest a course of treatment – if your fruit tree is salvageable.


Next: Part 3 – Fire blight treatment and management >>

more resources from CSU extension here.

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