How to Manage Pests

Pests in Gardens and Landscapes

Wetwood, or slime flux—Various microorganisms

Wetwood is caused by several species of bacteria; yeast organisms may also be involved. Wetwood is especially common in elm and poplar, but it affects many other plants, including box elder, fruitless mulberry, hemlock, magnolia, maple, and oak. Although it can be unsightly, limbs infected with wetwood may be as strong as healthy wood.


Wetwood is an area of branches or trunks that is discolored, water soaked, and exuding sour or rancid, reddish or brown fluid from bark cracks or wounds. Foliage wilt and branch dieback may occur on severely infected trees, but the disease rarely causes serious harm to trees.

Foamy canker, or alcoholic flux, also causes wood to exude fluid. Foamy canker causes oozing for a short time during the summer and that fluid has a pleasant, fermentative odor.

Foamy bark canker also causes discolored, oozing bark, but only on coast live oak. Infected oaks may die back or be killed by foamy bark canker disease.

Life cycle

Wetwood-causing microorganisms are common in soil and water and infect trees through wounds. The bacteria, including Clostridium spp. and others, grow within the tree using the sap as a nutrient source and causing fluid to exude from bark. Usually only trees about 10 years of age or older exhibit symptoms of wetwood, or slime flux.


Avoid injuries to bark and wood. The microorganisms that cause wetwood infect through wounds, including sites where pesticides have been injected into trees.

Wetwood infection
Wetwood infection causes stained wood

Alcoholic flux on almond
Alcoholic flux on almond

Statewide IPM Program, Agriculture and Natural Resources, University of California
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