Bacterial Wetwood and Alcoholic Flux

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Flux, an oozing, frothy liquid on the outer surface of a tree has various causes. The problem is seen in many kinds of trees and may occur on the main trunk, branches, flare roots, and roots of old trees or young saplings. Flux is especially common in trees that are environmentally stressed or recently transplanted. The first external symptom is an eye-catching, often alarming, wet seepage from a small area. If the flux has a foul or sour smell, it is a disease which is variously named bacterial wetwood, slime flux, or bacterial flux. If the flux is milky colored and very frothy/foamy and smells like alcohol, sometimes mixed with a vinegar-like or a sweet odor, it is called alcoholic flux and is not the result of disease.

Bacterial wetwood begins deep inside the tree and is bacterial in origin, while alcoholic flux originates just under the bark, usually near a wound—most commonly, pruning wounds. In both cases, the external flux is colonized by yeasts, bacteria, and fungi, which can modify the colors and odors of the flux. The overall symptoms of the problem vary over geographic areas because of environmental factors.

Alcoholic flux, also called white flux, foamy flux, or frothy flux is not related to bacterial wetwood. It occurs in the outer cambial region in shallow cracks, bark wounds, and especially pruning wounds. Alcoholic flux, nearly colorless and resembling frothy white shaving cream, seems to be generated by microorganisms—probably yeasts—producing gas and alcohol. The odor of the alcohol is attractive to insects and persists only a short time in summer. Alcoholic flux is often associated with drought and heat stressed trees. It has also been noted on mimosa trees infected by Fusarium wilt (a fungal disease that damages the xylem or water conducting tissue). This publication highlights cultural management practices for bacterial wetwood that are appropriate for alcoholic flux as well. You can also contact state Extension specialists or your local Extension office for answers to specific questions.

This work is supported by Crop Protection and Pest Management, Extension Implementation Program, award no. 2024-70006-43496 from the USDA National Institute of Food and Agriculture.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S. Department of Agriculture.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

Information Sheet 1664 (POD-04-25)

By Alan Henn, PhD, Extension Professor, Agricultural Science and Plant Protection.