Bacterial canker
A bacterial disease of stone fruit that kills branches from sunken cankers on the bark, oozing amber gum, while the leaves carry small brown spots whose centres fall out and leave clean round holes. The two signs are usually on the same tree and are the reason it can be told from silver leaf without cutting anything.
Caused by: Pseudomonas syringae pv. morsprunorum and pv. syringae · also called gummosis, shot hole
Nothing available to a home grower will fix this
There is no chemical control available to a home grower in the UK. Copper sprays are used commercially in some systems and are not an amateur option here, so the response is pruning timing, cutting out and — where the trunk is affected — replacement.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Bacterial canker
Checked 2026-08-13
What brings it on
The bacteria enter through leaf scars and wounds in autumn and through frost-damaged tissue in spring, and multiply on the leaf surface in wet weather. Cold wet springs and exposed sites make it markedly worse.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Bacterial canker
- Agriculture and Horticulture Development Board — AHDB: Stone fruit — bacterial canker
Checked 2026-08-13
Usually seen: September, October, November, March, April, May, June
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Prune plums and cherries between late spring and midsummer only. The same summer-pruning rule that keeps silver leaf out keeps this out, because both infect through wounds in the damp half of the year.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Pruning plums and cherries
Checked 2026-08-13
- Choose a resistant rootstock and cultivar where the site is cold or exposed, and stake young trees so the bark is not chafed. Most infections start at a wound.
source
Horticultural consensusmoderate confidence
- MSU Extension — Michigan State University: Bacterial canker of stone fruit
Checked 2026-08-13
Dealing with it once it is there
- Cut affected branches back into clean healthy wood in summer, well below the lowest sign of staining or gum, and burn or bin the prunings rather than composting them.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Bacterial canker — control
Checked 2026-08-13
- A tree cankered on the main trunk will not recover and is best replaced. One with a single affected limb often lives for years after that limb comes off.
source
Horticultural consensusmoderate confidence
- Agriculture and Horticulture Development Board — AHDB: Stone fruit — bacterial canker
Checked 2026-08-13
Widely repeated, and not supported
Recorded so GrowingHQ can address them. These are not alternative approaches — they are things the evidence does not back.
“Gum oozing from the bark always means bacterial canker.”
Stone fruit gums for several reasons — physical injury, a hard frost, waterlogging and borers all do it, and a healthy plum will gum from a pruning cut. Gum matters diagnostically only when it comes with a sunken dying patch of bark or with shot-holed leaves above it.
Horticultural consensusCommonly said, not supportedmoderate confidence
- MSU Extension — Michigan State University: Bacterial canker of stone fruit
Checked 2026-08-13
What it affects
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.