Yellow Sap Oozing from an Old Red Maple: Bacterial Wetwood?

The Symptoms

An 80‑year‑old red maple in New York has a large trunk cavity that recently started oozing yellow sap, staining the bark dark and wet. The liquid may have a fermented odor and attract insects.

Likely Diagnosis

Bacterial wetwood (slime flux)—a common condition in mature maples, elms, and oaks. Bacteria enter through wounds, ferment sap, and produce gas pressure that forces liquid out.

What to Do

• No cure exists, but the tree can live decades with wetwood.
• Reduce stress: Water during drought, apply a slow‑release fertilizer in spring, avoid further trunk injury.
• Do not plug the hole—trapping gas increases internal pressure.

Confirmation

Search “bacterial wetwood” images online. If the match is good, manage for tree vitality rather than trying to stop the flow.