Foul-smelling, slimy, weeping wounds on trees could be a conditions known as slime flux. The condition is caused when bacteria grow in fluids seeping from cracks or wounds in trees, or from crotch areas where fluids can accumulate. It is associated with a condition called wetwood that affects inner portions of the tree. Many species of tree can be affected, but slime flux and wetwood are most commonly found in elms and poplars, including the cottonwoods. It can also affect aspen, fir, maples (including box elder), white pine, mountain ash, paper birch, and others.
Usually, slime flux and wetwood in landscape trees is unimportant except for the undesirable appearance of the dark fluids seeping down the trunk of the tree. Severe infestations can sometimes cause foliage on upper branches to wilt and branches to die back. It does not result in tree mortality, however.
It is fortunate the damage is not severe, because there are no known cures. Drain tubes can be installed by tree care professionals for cosmetic purposes, allowing the fluids to drop to the ground rather than running down the side of the tree. Note: drilling holes in trees with this condition can spread the condition to other portions of the tree. For the most part, there is little you can do, or should do.
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Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997