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Branch cankers

slight protrusion in thin branch

Bacterial canker in cherry branch

M. Grabowski, UMN Extension

A canker is an infection that kills the bark. Cankers first appear as dark discolored areas of the bark. The infection often starts as a small oval or circle. In cherries, the bark next to the cankers often exudes gum. As the infection spreads, the branch may be girdled, killing the branch above the canker. Cankers can occur on small twigs hidden within the tree canopy, on large branches, or on the main trunk. Cankers on large branches or the trunk can kill the tree. Cankers can be caused by several different pathogens, but the most common canker causing organisms in Minnesota are the bacteria Pseudomonas syringae pv. syringae and P. morsprunorum and Cytospora spp. fungi. Bacterial cankers are most common on cherry trees, while Cytospora can be found on apricots and plums as well as cherries. Canker causing pathogens survive in infected branches and twigs. Both pathogens are spread by splashing water from one part of the tree to another and infect through wounds and natural openings.

Cankers can be controlled by minimizing injury to the bark and by removing diseased branches. Prune young trees to encourage strong healthy branches. Pruning should be done during the first warm, dry weather in early spring to promote quickly healing of the pruning cut. Never leave a branch stub as these can be points of entry for canker causing and wood rotting pathogens.

Prune out branch cankers four inches below the visibly infected section of the branch. Sterilize pruners with rubbing alcohol, 10% household bleach, Lysol, or Listerine after pruning out infected branches. Burn or bury infected branches. Avoid hammering nails into the bark of cherry trees or damaging the bark in other ways.

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