Key takeaways
- Sticky amber gum plus round holes in the leaves points to bacterial canker
- It attacks cherries, plums, damsons, apricots and ornamental Prunus
- Bacteria enter through wounds and leaf scars in cool, wet autumn and winter weather
- Prune cherries and plums only in dry summer weather, never in winter
- Cut cankers out back into clean wood and wipe tools clean between cuts
- There is no spray for gardeners, so prevention matters most
Sticky amber gum oozing from sunken bark on a cherry or plum, with small round holes in the leaves, is the classic sign of bacterial canker. It’s caused by bacteria that get into wounds and leaf scars in cool, wet weather. There’s no spray for gardeners, but pruning at the right time and cutting cankers out keeps most trees going for years.
This guide covers stone fruit and ornamental cherries. For apple and pear canker, which is a fungus, see our wider guide to canker in fruit trees.
How to identify bacterial canker
Look for two signs together: gum on the bark and holes in the leaves.
- Gum: amber to brown sticky gum oozing from cracks on branches or the trunk.
- Sunken bark: flattened patches of dead, darker bark, often on one side of a branch.
- Shot-hole leaves: small brown spots that dry and drop out, leaving round holes. You’ll see these in late spring and summer.
- Failing shoots: buds that don’t open in spring, or branches that suddenly wilt and die in summer.
Gum on its own isn’t proof. Cherries and plums also gum after frost damage, knocks and pest attack. Gum on the stems and shot-holes on the leaves of the same tree points to bacterial canker.
It hits cherries (fruiting and flowering), plums, damsons, gages and apricots. Peaches and nectarines can get it too.
Brown spots that drop out to leave neat round holes are the leaf sign of bacterial canker. Spot these alongside gum on the bark and you can be fairly sure.
Is it bacterial canker or something else?
| Problem | How it differs |
|---|---|
| Frost or injury gumming | Gum, but no shot-holes and no sunken patch |
| Silver leaf | Silvery sheen to the leaves, dark stain in cut wood, no gum |
| Brown rot and blossom wilt | Flowers and fruit rot with pale fungal pustules |
| Peach leaf curl | Red, puckered, blistered leaves on peaches and nectarines |
| Apple canker | Sunken, ringed cankers on apples and pears, not stone fruit |
How does bacterial canker get into a tree?
The bacteria live harmlessly on leaves for much of the year. They only cause trouble when they get inside, through leaf scars in autumn, pruning cuts and other wounds, and sometimes through blossom in spring.
Cool, wet weather from autumn to early spring is when this happens. Rain splashes the bacteria about, and wounds stay damp and open. In summer, warm, dry weather helps cuts heal fast, so the risk is much lower.
That’s why the timing of your pruning matters more than anything else.
When to prune cherries and plums
Prune cherries, plums, damsons and apricots only in dry summer weather, roughly June to August. Never prune them in autumn or winter.
Summer cuts dry out and seal within days. Winter cuts stay wet and open for weeks, just when the bacteria are most active. A single winter tidy-up can let canker into a healthy tree.
Our guide on how to prune fruit trees covers summer pruning cuts in detail.
Warning: Don’t prune any cherry, plum, damson or apricot between autumn and early spring. Winter wounds are the main way bacterial canker gets into a healthy tree.
A branch suddenly dying in summer while the rest of the tree stays green often means a canker has ringed it. Cut it back to clean wood straight away.
How to cut out bacterial canker
There’s no spray for home gardeners, so cutting out infected wood is the main treatment. Do it on a dry day in summer.
- Find the whole canker. The dead bark often stretches further than the gum suggests.
- Cut well below it. Go back into clean, healthy wood with no brown staining under the bark.
- Make a clean cut just above a bud or at the branch collar, without leaving a stub.
- Wipe your tools with a garden disinfectant or surgical spirit between cuts and between trees.
- Bin the prunings. Don’t compost or chip them.
- Leave the wound unpainted. It seals best on its own in dry air.
If a canker rings the main trunk of a young tree, it won’t recover. Replace it, ideally in a different spot.
Summer is the safe time to cut out canker. Dry weather helps the wound seal before autumn rain returns.
A quick wipe of the blades between cuts stops you spreading the bacteria from a diseased branch to healthy wood.
Why do some trees keep getting canker?
Most repeat cases come down to three things.
Winter pruning. It’s the biggest cause. Mower damage and rubbing tree ties also make wounds, so check these too.
Wet ground. Trees growing in heavy, waterlogged soil are stressed and more prone to infection. Don’t plant new stone fruit in the wettest part of the garden.
Variety. Some varieties suffer more than others. Plum ‘Victoria’ is quite prone, so give it a well-drained spot and strict summer pruning. Plum ‘Marjorie’s Seedling’ and cherry ‘Merton Glory’ are usually less troubled. No cherry or plum is immune.
Our guides to the best cherry tree varieties and growing plum trees help you choose and care for a tree that suits your garden.
Smooth, healthy bark on the left and a sunken, cracked canker on the right. Cut well below the lowest edge of the dead bark.
Bacterial canker calendar
| Month | What to do |
|---|---|
| January to March | No pruning. Look for gum and sunken bark, and mark cankers to deal with in summer |
| April and May | Watch for buds that don’t open, wilting shoots and shot-holes in new leaves |
| June to August | Prune and cut out cankers in dry weather. Clean tools between cuts |
| September | Stop pruning. Rake up and bin fallen spotty leaves |
| October to December | Leaf fall is the riskiest time, so keep tools away. Plant replacement trees on well-drained ground |
A replacement tree on well-drained ground, firmly staked, is set up well. Its first pruning can wait until next summer.
Common mistakes with bacterial canker
- Pruning in winter. Wait for dry summer weather.
- Cutting too close. The infection spreads beyond the gum, so cut well into clean wood.
- Using dirty tools. Wipe blades between cuts and between trees.
- Painting wounds. Paint can trap moisture. Leave clean cuts to seal on their own.
- Replanting in the same wet spot. Improve drainage or choose a better position first.
For care through the whole year, see our cherry growing guide, and there’s more on healthy trees in the fruit growing hub.
Frequently asked questions
What are the first signs of bacterial canker on a cherry tree?
Amber gum oozing from sunken bark, and small round holes in the leaves. Brown leaf spots dry and drop out to leave the holes. Some shoots may fail to open in spring or wilt and die in summer.
Can bacterial canker be cured?
No, there is no cure or spray for home gardeners. You manage it by cutting out infected wood in summer and preventing new infections. A young tree with canker on its main trunk is usually best replaced.
When should I prune a cherry or plum tree to avoid canker?
Prune only in dry summer weather, never in autumn or winter. Summer cuts dry and heal quickly. Winter cuts stay wet and open, which lets the bacteria in.
Is bacterial canker the same as apple canker?
No, they are different diseases. Apple canker is caused by a fungus and affects apples and pears. Bacterial canker is caused by bacteria and mainly affects cherries, plums and other stone fruit.
Will bacterial canker spread to my other trees?
It can spread to other cherries and plums nearby. Rain splashes the bacteria onto leaf scars and wounds in autumn and winter. Prune in summer and clean your tools between trees to limit spread.
Can a tree recover from bacterial canker?
Yes, if the cankers are small and the tree is growing well. A canker that rings a branch kills everything above it. Cut those branches back to clean wood in summer.
Should I paint pruning wounds after cutting out canker?
No, wound paint isn’t needed and can trap moisture. Make a clean cut in dry summer weather and let the tree seal it naturally. Clean tools matter far more.
Now you can spot and manage bacterial canker, read our guide to growing a flowering cherry if it’s an ornamental tree you’re looking after.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
