Bacterial canker

Pseudomonas syringae

A bacterial canker of cherries and plums: sunken oozing patches on the bark that girdle branches, with shot-holed leaves and dying buds.

Bacterium Serious Rain splashAirborne sporesSpread on tools & hands Spreads to neighbors

What you'll see

Sunken, flattened cankers on the trunk and branches ooze amber gum, especially in spring.
A girdled branch above a canker fails to leaf out, or wilts and dies back in summer.
Leaves carry small brown spots that dry and fall out, leaving a peppering of shot-holes.
Buds and spurs fail to break in spring and die.
Small round spots may also scar the fruit.

Why it happens

A bacterium that lives on the leaves and bark and enters through leaf scars, pruning cuts and frost and wind wounds. Autumn leaf-fall and winter injury give it its way in, and it multiplies in the bark over winter.

Cool wet weather in autumn and spring favors infection; young trees, and those on frost-prone or stressed sites, are hit hardest.

Treating it

Cut out cankered wood well below the sunken bark in summer, when the trees resist infection best.
Bin or burn the prunings and disinfect the saw between every cut.
Feed, water and mulch a struggling tree to help it wall off the canker and recover.
Remove a badly girdled or dying young tree, as it will not come back.
A copper-based spray in autumn at leaf-fall can reduce fresh infection.

Keeping it away

Prune stone fruit only in summer, never in the dormant winter, so wounds heal before the wet.
Plant on a sheltered, well-drained site and stake young trees against wind rock.
Choose canker-resistant rootstocks and cultivars where you can.
Keep trees unstressed with steady water, mulch and a balanced feed.
Disinfect pruning tools between trees.

Who gets it

Cherries and plums above all, along with other stone fruit such as peaches, apricots and ornamental Prunus.