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( Pseudomonas monsprunorum )

image of bacterial canker on cherry tree
Weeping sap from a cherry tree

Affects apple trees and members of the Genera Prunus - ie. the stoned fruit such as plum, cherry or apricot. A swollen area on the bark exudes a light brown gum, usually near the angle of branches. If the swelling encircles the branch it is killed.
Wind or water-borne bacteria enter leaf scars and pruning wounds during the autumn. Young leaves can be infected in May or June, a brown spot about 2mm accross develops, the dead tissue falls out leaving a hole similar to - "shot hole".

Some varieties of Prunus are resistant. Infected branches should be pruned out and burnt, but usually the disease progresses over a number of years and the tree eventually dies back completely.

Arbrex wound paint can be applied to pruning scars, but there is some evidence that this may not be best practice. It would be best to observe the growth of the tree and prune out branches when they are small, anticipating where they might eventually end up; this would keep pruning scars small. An autumn spray of Bordeaux Mixture may prevent infection.

See also Bleeding Canker and Phytophora

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