Fungal Canker & Dieback
A canker is a localised dead area of bark and underlying wood caused by fungi or bacteria that invade through wounds, pruning cuts, frost cracks, or…
Fungal Canker & Dieback at a glance
| Also known as | Canker, twig blight, branch dieback |
|---|---|
| Affected parts | Bark, branches, trunk |
| Most at risk | Stressed or wounded woody species; Prunus (ume, cherry), larch, junipers, fruiting trees |
| Main cause | Fungi/bacteria entering through wounds or stress points |
| Severity | Serious — can girdle and kill branches or the trunk |
| Reversible? | Local — cut out infected wood; a trunk canker can be fatal |
What to look for
- Leaves: Leaves on the affected branch wilt, yellow, brown, and hang on; the branch dies back from the tip.
- Whole tree: One branch or section declining and dying while the rest looks healthy; dieback progressing toward the trunk.
Overview
A canker is a localised dead area of bark and underlying wood caused by fungi or bacteria that invade through wounds, pruning cuts, frost cracks, or stress points. As the canker expands it strangles the flow of water and nutrients, so the branch (or trunk) beyond it wilts and dies back. Cankers are most common on stressed, wounded, or recently hard-pruned trees.
Causes
Infection through pruning wounds, wire scars, frost cracks, or insect damage; trees stressed by drought, overwatering, frost, or over-working; unsanitised tools spreading pathogens (e.g. Prunus canker, Nectria, Phomopsis).
Commonly confused with
Wire bite makes even spiral swellings without sunken dead bark. Mechanical/old wounds lack spreading dieback. Root rot kills from the roots up (whole-tree decline). A localised sunken, dying bark patch with dieback beyond it points to canker.
Which species are affected
Many woody species, especially when stressed or wounded; Prunus (ume, flowering cherry, apricot) are notably canker-prone, as are larch, junipers, and fruiting trees.
Treatment
Prune out the affected branch well below the canker into clean, healthy wood, sterilising the tool between every cut (e.g. 10% bleach or alcohol). Don't prune in wet weather. Seal large cuts if appropriate for the species. Reduce the stress that let it in (correct watering, placement). Remove and bin infected prunings. A trunk canker may not be curable.
Prevention
Use clean, sharp, sterilised tools; prune at the right time and avoid wet weather; keep trees unstressed and vigorous; protect from frost cracks and avoid unnecessary wounds; treat pests/wire promptly.