Lately, we have had many questions at the Plant Clinic about liquid oozing from trees. Often, trees have seepage coming from a major crotch or wound in the trunk. This condition is called bacterial wetwood.

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, and maples seem most commonly affected in Illinois, but probably any tree is susceptible. Bacterial wetwood is a chronic, rarely serious, 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 called slime flux is left. 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 practices may be helpful. Fertilize stressed trees in the spring to stimulate vigorous growth. Some persons 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 Disease No. 656 for more on this condition.