Sap or ooze running from a trunk: what the sources say it may indicate

This page reports what the named sources say. It does not say whether any tree has a disease, whether it is healthy or what should be done with it. The sources describe a condition called slime flux or wetwood, and the University of Maryland Extension page says a certified arborist can be contacted for an onsite evaluation if the tree is not otherwise healthy.

What the University of Maryland Extension describes

The University of Maryland Extension page Tree Trunks with Wet Wood or Slime Flux, updated February 28, 2023, gives the most obvious symptom as sap flowing from bark cracks or other wounds in the trunk or branches. The table sets out the points it lists.

Topic	What the page says
How it looks	The flow may be heavier at certain times of year, or may stop and then start again. It leaves dark streaks on the bark that can turn gray or white when dry.
Smell	The liquid may smell fermented or alcoholic when fresh.
Cause	Common bacteria or yeast fungi that live on the surface invade wounds and feed on the sap. Gas from these microorganisms builds pressure that forces the sap out of the wound.
Trees named	Elm, oak and mulberry most often, and to a lesser extent maple, birch, butternut, redbud, sycamore and walnut.
Effect on the tree	It can slow callus formation and wound healing. A tree may be injured but not show slime flux for several years. Formerly water-soaked wood may also be open to attack by wood decay fungi.
Treatment	The page says no treatment cures a tree with these symptoms, and that unless the tree is in decline the symptoms are only monitored. It says a certified arborist can be contacted for an onsite evaluation if the tree is not otherwise healthy.

What Utah State University describes

The Utah State University Extension integrated pest management page Slime Flux calls the condition bacterial wet-wood and says bacteria enter through open wounds in the bark, including small ones. It lists wounds from pruning done badly, insect borers, weak branch angles, tree houses and mowers as the more common ways in. It separates two types in Utah. In the heartwood type, internal pressure of up to 60 pounds per square inch pushes ooze through cracks that reach the bark, the flux kills bark and grass it touches, and trees are rarely killed. In the bark and cambial type, which it describes in willow, the page says infections frequently end in the death of the tree within 1 to 2 years.

A Utah State University Forestry Extension answer, Siberian Elm Slime Flux, sent May 11, 2020, was written for an owner whose Siberian elm had it. The extension educator says slime flux is not visually appealing, typically is not harmful to trees and occurs in response to a previous wound.

Where the sources differ and agree

The three pages agree that the flow follows a wound and that bacteria are involved. They differ on seriousness: The Siberian elm answer says slime flux typically is not harmful to trees, Maryland says no treatment cures it and that unless the tree is in decline the symptoms are only monitored, while the Utah State page describes one type that frequently ends in death within 1 to 2 years. The sources do not say which applies to a given tree. The guide on slime flux and wetwood describes the terms arborists use, and the guide on whether a tree is dying reports who the sources say assesses trees.

Who to call

ISA Find an Arborist: the ISA directory for an arborist who can examine a tree
Consulting arborists by country: the credentials and registers consulting arborists hold in each country
University of Maryland Extension: the extension service that published the page; other states have their own extension offices