Why is my peach tree oozing amber gum from the bark?

Clear to amber sticky gum oozing from the bark or branch junctions of a peach or nectarine tree — a symptom called gummosis — is not a disease in itself but rather the tree's response to damage or stress. The gum is composed of complex carbohydrates that the tree exudes when bark tissue is injured. Identifying the underlying cause is essential before you can fix the problem.

Bacterial canker: the most serious cause

When gum appears at a sunken, discoloured patch on the bark — particularly on branches or the main scaffold during or after winter — bacterial canker (Pseudomonas syringae) is the most likely cause. The bark beneath the gum site will be brown, soft, and dead when you cut into it. Treat by removing all affected wood to clean tissue, sealing cuts, and implementing a copper spray programme in autumn and winter.

Cytospora canker (fungal gummosis)

The fungus Cytospora leucostoma causes a similar pattern to bacterial canker, with bark discolouration and gum exudate, but typically produces small black fruiting bodies in the dead bark. It tends to infect through wounds and frost damage. Treatment is the same: cut out all infected wood to healthy tissue in summer, sterilise tools between cuts, and seal wounds.

Borer damage at the crown

In some regions, the larvae of clearwing moths or shot hole borers tunnel into the bark near the soil line and lower trunk, causing masses of gum mixed with sawdust-like frass around the entry holes. If you see frass with the gum, probe the wound carefully for a larval tunnel. Borers can be controlled by mechanical removal of larvae with a piece of wire, or by injecting a biological control (Steinernema nematodes in water) into the tunnel.

Mechanical wounds and frost damage

Minor gummosis at pruning cuts, areas of bark split by frost, or points of physical damage is completely normal and does not indicate disease. The gum dries and seals the wound. If the gum comes from a clearly identifiable wound site and the surrounding bark is healthy and green beneath, no action beyond sealing the wound is necessary.

Improving tree vigour

Chronic stress — from waterlogging, compacted soil, drought, or poor nutrition — can trigger persistent gummosis even without a specific pathogen present. Address the root cause: improve drainage, aerate compacted soil, mulch the root zone, and apply a balanced spring fertiliser. A well-growing tree has the resources to compartmentalise wounds quickly and will produce less gum over time.