Peach, cherry, plum and apricot trees all bleed a thick, amber gum when the bark is damaged. The oozing has a name, gummosis, but it is a symptom rather than a cause. The job is to find out what wounded the tree. In most backyards the answer is one of three things: peachtree borer, a canker disease or plain physical injury.

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The short answer: look at where the gum is and what is mixed into it. Gum at or just below the soil line with sawdust-like bits in it points to peachtree borer. Gum oozing from sunken, darkened patches of bark higher up, with no sawdust, points to a canker such as cytospora. Gum at a fresh wound from a mower, string trimmer, hail or a pruning cut is injury. Each needs a different response.

Quick diagnosis

Where and what	Most likely cause
Gum at the base of the trunk, mixed with sawdust or frass	Peachtree borer
Gum from sunken, dark, cracked bark on branches or trunk	Cytospora (perennial) canker
Gum at a scrape near ground level	Mower or trimmer injury
Gum on the south or southwest side after a cold winter	Winter injury or sunscald
Small beads of clear gum on young shoots after hail	Hail damage

Peachtree borer

The greater peachtree borer is the larva of a clearwing moth that looks a little like a wasp. Females lay eggs on the lower trunk in summer, and the larvae tunnel into the bark at or just below the soil line. Colorado State University Extension describes the main sign as gummy, oozing sap at the base of the trunk, often darkened by sawdust-like excrement from the larvae.

Borer damage builds up. Oklahoma State University Extension notes that heavy or repeated attacks can kill a peach tree over several years.

What you can do:

Pull back mulch and a little soil at the base and look for gum with frass, small holes and soft bark.
On a few trees, larvae can be dug out carefully with a knife or a stiff wire pushed into the tunnel. Remove as little healthy bark as possible.
Insecticides labeled for peachtree borer on home peach trees are applied to the lower trunk while the moths are laying eggs, which Oklahoma State places in July and August for their region. Timing differs by location, so check with your extension office and follow the label.

Cytospora (perennial) canker

Cytospora canker is a fungal disease of stone fruit. The fungus is weak and mostly enters through wounds, such as winter injury, pruning stubs, insect damage and mower strikes. Ohio State University Extension describes gummy drops around wounded bark in early spring, followed by sunken, dying bark. Over the years, a series of dead callus ridges forms as the tree tries to wall off the infection and the fungus keeps pushing back. A branch beyond a canker that circles it will die.

The Missouri Botanical Garden points out a useful clue: canker gum does not have sawdust or bark bits mixed in, unlike borer or mechanical damage.

Fungicides are generally ineffective against the cankers themselves, according to Ohio State. Management focuses on the tree:

Prune out dead and cankered branches in dry weather, cutting well into healthy wood, during late winter or as the tree is coming into bloom, when wounds close faster.
Avoid leaving stubs. Cut just outside the branch collar.
Reduce wounds of every kind: keep trimmers away, paint the trunks of young trees with white interior latex paint diluted with water to reduce winter sunscald, and control borers.
Keep the tree vigorous with steady watering and moderate feeding based on a soil test.

Mechanical and weather injury

Oklahoma State lists mowers, string trimmers, hail, freeze events and sunscald as common triggers for gummosis. The fix is mostly prevention: a weed-free mulch ring around the trunk, care around the tree with equipment and good watering so the tree can seal the wound. The gum itself is the tree’s way of sealing the wound. You do not need to scrape it off, and painting wounds with sealant is not recommended.

What not to do

Do not cut out large areas of bark around gum spots hoping to remove the problem. You can create bigger wounds than the original.
Do not over-fertilize. Soft, fast growth is more prone to winter injury and canker.
Do not leave dead or cankered wood in a pile near the tree.

When to get help

If gum is coming from many places, the tree is losing large branches, or you see cankers on the main trunk, contact your county extension office for a diagnosis, or a certified arborist for an on-site assessment. You can find one through the ISA Find an Arborist directory. A canker that circles the trunk usually means the tree is in decline.

Other peach problems are covered in how to get rid of peach leaf curl and why a peach tree did not bloom. For more, see the Fruit Trees hub.

Sources

Peachtree Borer, Colorado State University Extension
That's Not Peach Jam: Diagnosing Gummosis, Oklahoma State University Extension
Peach Canker, Ohio State University Extension, Ohioline
Gummosis of Fruit Trees, Missouri Botanical Garden

Top photo: I.Sáček, senior, CC0, via Wikimedia Commons

Why Is My Peach Tree Oozing Sap?