Bacterial canker commonly affects members of the prunus family causing sunken lesions in the bark in spring which is often accompanied by oozing gum, and small holes in the leaves from early summer.
Unfortunately once canker has infected the tree in spring there is little that can be done to save your crop this year.
Prune all infected wood from mid to late summer back to healthy wood and paint the pruning cuts with wound paint to prevent bacteria re-entering the wounds. Apply a copper based fungicide in autumn as the leaves fall, and repeat this application several times throughout the winter. This should help to prevent a recurrence of the problem next year. However, if the tree is particularly badly affected then you may wish to replace it. It would be preferable to plant your replacement tree in a different location. But if this is impossible then I would recommend getting into the habit of spraying your replacement tree with copper fungicide in autumn and winter as a preventative measure.
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