Why Does My Apple Tree Have Canker Oozing from the Bark?

Sunken, cracked, discoloured areas of bark on apple tree branches or the trunk — sometimes weeping a reddish-brown liquid, sometimes showing concentric rings of dead and cracked tissue — are the characteristic signs of apple canker, caused by the fungus Neonectria ditissima (formerly Nectria galligena). Canker is one of the most serious apple diseases in cool, wet climates because it attacks the wood itself rather than just the leaves or fruit, and if allowed to spread unchecked it can girdle and kill entire branches, or in severe cases the whole tree.

Identifying apple canker

Look for sunken, elliptical lesions in the bark, with the surrounding bark cracking and peeling away to reveal dead, reddish-brown or orange-brown wood underneath. The bark surface may show small, cream-coloured or red cushion-like spore-producing bodies in the lesion margins. In winter, the dead area may be surrounded by a raised, callus-like border where the tree is attempting to wall off the infection. As the canker expands around the branch, it eventually girdles it — the wood beyond the canker dies and the branch fails to produce leaves in spring.

How canker spreads

The canker fungus enters the tree through pruning cuts, damaged bark, scab lesions, frost damage, and leaf scars. It is most active in autumn and winter, with spore release during wet weather. Trees growing in wet, poorly drained sites, or with heavy scab infections (which create many entry points), are significantly more susceptible than trees in well-drained conditions with good disease management.

Cutting out canker

The only effective treatment is physical removal of infected wood. Use a sharp, clean knife or pruning saw to cut back to completely clean, healthy wood — the cut surface should show no discolouration. For small lesions on large branches, cut out the lesion with a clean knife, removing all infected tissue plus 2–3 cm of healthy wood around it. Disinfect tools between cuts with a dilute bleach or Jeyes fluid solution. Seal large wounds with wound paint. On small branches, cut the branch off entirely below the lesion.

Prevention

Plant in well-drained soil. Prune in dry weather to minimise wound infection. Manage scab to reduce entry points. Choose resistant varieties — Cox is particularly susceptible; Bramley and many modern varieties show much better canker resistance.