Bacterial Canker
Pseudomonas syringae
A bacterial disease of cherries, peaches, apricots, plums, and other stone fruit that forms oozing cankers on the trunk and limbs and blasts blossoms, buds, and shoots in spring. It is worst on young, stressed trees in cool, wet springs and can girdle and kill whole limbs or young trees.
🔎 How to spot it
Look for sunken, dark cankers on the trunk, limbs, and twigs that ooze amber gum, often with a sour-smelling sap seeping from the wounds when the tree breaks dormancy in spring. Dormant buds fail to open and die, blossoms and young shoots suddenly wilt and blacken in a symptom called blossom blast, and small dark spots may appear on leaves and later drop out to leave a shothole look. Limbs above a girdling canker wilt and die back.
🥀 Damage it causes
The bacteria kill patches of bark and cambium, forming cankers that can girdle and kill twigs, scaffold limbs, and entire young trees, while spring infections blast the flowers, buds, and shoots and cut the crop. Trees two to eight years old are hit hardest, and severe cases can deform or destroy a young orchard. Stressed and frost-injured trees suffer the most.
🔬 What causes it
Bacterial canker is caused by the bacterium Pseudomonas syringae, which lives on the tree surface and enters through wounds, pruning cuts, leaf scars, and frost-injured tissue, then is spread by splashing rain and wind. Cool, wet spring weather favors infection, and the disease is worse on trees stressed by ring nematodes, poor or sandy soils, low pH, and winter or frost injury.
🛡️ Prevent it
Keep trees vigorous and unstressed, since healthy trees resist and wall off the bacteria far better: plant on well-drained sites, correct soil pH, manage ring nematodes, and protect trunks from winter and sunscald injury. Prune in dry summer weather rather than wet winter conditions so cuts dry quickly and are less likely to be infected, and choose less susceptible rootstocks and varieties. Avoid wounding the bark.
🧯 If it is already here
There is no cure that eliminates the bacteria, so management is preventive and cultural: cut out cankered wood well below the canker during dry weather, disinfecting tools between cuts, and remove and destroy badly affected young trees. Copper sprays applied around leaf fall and again in late winter can reduce surface bacteria but give variable results. The most reliable defense is keeping trees healthy and avoiding spring wounds.
💡 Good to know
Bacterial canker thrives where stone fruit is stressed, so the real fix is often improving the site and tree vigor rather than chasing the bacteria with sprays. The sour-smelling spring ooze and blasted, blackened blossoms help separate it from fungal cankers and brown rot. Summer pruning in dry weather is one of the simplest ways to keep new cuts from becoming infection sites.
🌱 Plants it affects
17 plants in the library can be affected by this problem
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.