How to Manage Pests

Pests in Gardens and Landscapes

Pest identification and confirmation — Bacterial canker and blast

Bark infected with Pseudomonas syringae has infected cankers darker than the surrounding, healthy bark, and the underlying diseased tissue is reddish brown, moist, and may be sour-smelling. Cutting into infected bark beyond the margin of cankers may reveal small, brown flecks in the inner bark tissue, especially in apricots and plums. Affected limbs may fail to leaf out in the spring or may produce new growth, which dies soon after temperatures increase in the summer. If trees are killed by bacterial canker, new shoots are frequently produced from the rootstock. Bacterial blast symptoms seldom affects more than 1 or 2 inches of the shoot tip. The bark of twigs affected by bacterial blast is light tan and has a papery appearance. On apples and pears, bacterial blast often resembles fire blight. However, fire blight symptoms frequently extend 1 foot or more down the shoot and twigs have a dark brown or black, sunken, hard appearance of twigs. Grayish brown bacterial ooze is usually produced on fire blight lesions during humid or wet weather, but is never produced on tissue affected by bacterial blast.

Blossom blast infects fruit and leaves resulting in depressed black spots.

Blossom blast infects fruit and leaves resulting in depressed black spots.

Red flecks in wood beneath the main canker

Red flecks in wood beneath the main canker


Statewide IPM Program, Agriculture and Natural Resources, University of California
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