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
- 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.
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.
- 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.
- 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.
Cherries and plums above all, along with other stone fruit such as peaches, apricots and ornamental Prunus.
The Cottage Garden Companion — the gardener's apothecary at cottagegardencompanion.com