Wetwood and slime flux is a condition caused by bacteria that enter wounds in a tree. Enterobacter cloacae (formerly known as Erwinia nimipressuralis) and other bacteria are associated with this problem, and often the disease is called bacterial wetwood and slime flux. This condition in trees is very noticeable by the homeowner because infected trees often have seepage coming from a major crotch or wound in the trunk. In some cases, the liquid has a foul odor because secondary microorganisms colonize in this liquid, producing disagreeable smells.
Wetwood causes a water-soaked condition of wood in the trunk, branches, and roots of many shade and ornamental trees, especially old street trees. Elms, poplars, cottonwoods, oaks, and maples are most commonly affected in Illinois, but many other tree species are susceptible. This is a chronic, rarely seri-ous, 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. You cannot always see the wound, but you can see the liquid. Bacteria in the inner sapwood and heartwood of the tree ferment causing internal gas pressure. This pressure commonly reopens old wounds, and the sour liquid flows down the bark. As it dries, a light gray to white encrustation remains. This encrustation is called slime flux. The liquid commonly causes localized death of the cambium. Although fluxing occurs from April to December, it is most conspicuous in the summer.
There is no cure for this condition, but the following may be helpful. Fertilize stressed trees in the spring or fall 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. In other words, drain tubes often make the problem worse. Removing dead or weak branches plus promptly pruning and shaping bark wounds is helpful. Such measures encourage rapid callousing of wounds. The sap flow that results from pruned branches is normal and not the same as wetwood. The liquid we see with wetwood may flow year-round and is often followed by the foul-smelling slime flux just described. Consult Report on Plant Diseases No. 656, Bacterial Wetwood and Slime Flux of Landscape Trees, for more on this condition.