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Wetwood and Slime Flux of Trees

September 16, 1998

You likely have seen trees with seepage from a major crotch or wound in the trunk. Questions about this condition are fairly common at the Plant Clinic, especially since the condition is not easily sampled. We call this condition bacterial wetwood.

Wetwood causes a watersoaked condition of wood in the trunk, branches, and roots of many shade and ornamental trees, especially old street trees. Elms, poplars, cottonwoods, and maples seem most commonly affected in Illinois. This is a chronic disease of trees that can contribute to general decline in tree vitality but is not known to cause tree death.

Wetwood is most visible externally as a bubbling seepage of bacteria and toxins from wounded tissue in V-shaped branch crotches, pruning wounds, injection holes, and trunk cracks. Internal gas pressure commonly reopens old wounds; the sour liquid flows down the bark. As it dries, a light gray to white encrustation is left. This encrustation is called slime flux. The liquid commonly causes localized death of the cambium. The fluxing occurs from April to December but is most conspicuous in the summer.

There is no cure for this condition, but the following suggestions may be helpful. Fertilize stressed trees in the spring to stimulate vigorous growth. Some people like to install perforated plastic or iron drain tubes in the tree to relieve the gas pressure and to allow continual drainage away from the tree. The idea is to keep the liquid off the trunk so that the cambium is not killed. A disadvantage of drain tubes is that another deep wound is made, breaking the "compartment" that the tree has made to encompass the wetwood, thereby allowing the internal discoloration and any future decay to spread outside the wetwood-affected area. Removing dead or weak branches, plus promptly pruning and shaping bark wounds is helpful. Consult Report on Plant Diseases No. 656 for more on this condition.

Author: Nancy Pataky


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