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Bacterial Wetwood Or Slime Flux
Many mature trees, including elms, oak, tulip
poplar, and maple, exhibit large light or dark
vertical streaks on their trunks resulting from
slimy liquid oozing out of crack or wounds and
running down the bark. This is called 'slime
flux'.
Wetwood affected oak.
Cause And Effects
Bacteria, commonly found in soil and water, take up residence
in young trees or gain entrance to older trees through wounds.
The bacteria, including species of Clostridium, Bacillus,
Enterobacter, Klebsiella, and Pseudomonas, grow within the
tree using the sap as a nutrient source. As the sap is used,
oxygen in the heartwood is depleted (creating anaerobic
conditions), methane is produced, the pH of the sap is
increased (pH 6 in healthy trees to pH 7 to 8 in wetwood), and
a high pressure develops in the wood (60 psi in affected trees
vs. 5-10 psi in wetwood-free trees). The resulting environment
greatly inhibits the growth of fungi that can cause interior rots.
The liquid kills grass and other herbaceous plants that it
contacts at the base of the tree. The wood of affected trees has
greatly reduced value as lumber because of the unsightly
discoloration. Affected wood dries much more slowly than
wood taken from wetwood-free trees.
Management
• Avoid wounding the tree.
• Protect the tree from other stresses, especially soil
compaction from vehicles or pedestrians.
Sometimes this liquid is very abundant and foul smelling. If an
affected tree is cut down, the heartwood is darker in color than
surrounding wood, thus the name 'wetwood'. Although the
symptoms are unsightly, little damage is done to the tree in
most situations. However, if affected trees are under severe
stress from other factors such as soil compaction, wetwood
bacteria can move into the sapwood and cause leaf yellowing,
wilting, and a branch dieback.
Many years ago, it was thought that the pressure within the
tree should be relieved. Holes were drilled into the trunks of
affected trees and pipes were inserted to allow the liquid and
gases to escape. This is no longer recommended because 1)
affected trees generally survive well without any treatment
and 2) drilling holes in the tree creates yet another place where
slime oozes out.
Symptoms And Signs
• Light or dark streaks on the bark originate at a crack or
References Used In Preparing This Fact
Sheet
• Carter, C. J. 1964. The wetwood disease of elm. Illinois
wound and run vertically down the trunk
• Slimy, sometimes foul smelling liquid bubbles out of the
tree and runs down the trunk
• Heartwood deep in the interior of the tree is much darker
than surrounding sapwood.
Natural History Survey Circular 50. 19 pp.
• Sinclair, W. A. and H. H. Lyon. 2005. Diseases of trees
and shrubs. Cornell University Press, Ithaca, NY. 660 pp.
• Stipes, R. J. and Campana, R. J. (eds.) 1981. Compendium
of Elm Diseases. APS Press, St. Paul, MN.
Wetwood affected elm.
Prepared by Gary W. Moorman, Professor of Plant Pathology
Penn State College of Agricultural Sciences research and extension programs
are funded in part by Pennsylvania counties, the Commonwealth of
Pennsylvania, and the U.S. Department of Agriculture.
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by Penn State Extension is implied.
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Code: XL0009
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Bacterial Wetwood Or Slime Flux