Bacterial Canker

Pseudomonas syringae

Bacterial Canker, Canker

Photo by Stephen James McWilliam (CC BY 4.0)
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A close up of bacterial canker in a tree
Photo by Stephen James McWilliam (CC BY 4.0)
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Bacterial Canker is a disease caused by two bacteria, specifically targeting Prunus. Plums and Apricots tend to catch the disease most often; however, other ornamental Prunus can be affected, too. The main symptoms to look for include dark leaf spots, which eventually fall out, resulting in holes in leaves. In addition to leaf damage, Cankers, which look like sunken lesions in the bark, arise in the middle of spring. The disease is most severe in warm conditions. Nonetheless, Bacterial Canker can kill entire branches and small trees.


Elongated, sunken lesions on branches, which often ooze a gummy liquid, appear in spring to early summer. Please note, bark oozing liquids is common in Prunus plants and could be a result of other environmental stressors. New shoots may fail to emerge or grow before dying back suddenly. Dark spots on the leaf which eventually turn into 'shotholes'.

Growth factors

Having multiple wounds on the tree open it up to other infestations.


Sunken lesions in bark in mid spring to early summer.
Areas of bark become dark and shrivelled.
Lesions may ooze 'gummy' liquid.
Plants fail to form shoots.
Shoots which do form die back soon after emerging.
Small brown spots on leaves which turn into holes.
Leaf yellowing and dieback.
Whole branches can die.

Biological treatment

Cutting out infected branches. Prune back to healthy wood in the summer and apply wound paint. Consider completely removing badly diseased trees. When disposing of diseased material, make sure to abide by government advice and regulation or contact the local council to determine the safest methods.

Chemical treatment

There are no chemical treatments available to home gardeners.


The disease-causing bacteria inhabit plant tissues during winter. The bacteria move to the foliage during spring following wet weather, slowly spreading. Once the bacteria successfully enter the plant through the leaf stomata (pores), visible symptoms begin to arise. The pathogen exploits the plant tissues, resulting in dead patches on the leaves.


Maintain good airflow through and around plants by pruning every year. Ensure good plant hygiene by cleaning tools following pruning and removing and burning infected materials. Grow more resistant plants, such as ‘Merton Glory’, ‘Merton Premier’, ‘Merla’ and ‘Merpet’ cherries and ‘Marjorie’s Seedling’ and ‘Warwickshire Drooper’ plums.

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