Elm tree drips stinking sap

My elm tree has sap dripping from where a branch was cut several years ago. The wound from pruning has never healed. The sap smells horrible and my dogs roll in it when it drips on the ground. What can I do?

You have described "slime-flux" or "wet wood disease." This is a common problem with some of our faster growing shade trees - elms, mulberries, cottonwoods, poplars, and willows. It is due to a bacterial infection of the heartwood. The bacteria blocks the flow of water and nutrients in the trunk and a gas produced by the bacteria pushes the sap out through pruning cuts or cracks in the bark. The sap is caustic and can kill grass it drips onto. While it will not harm your dog, yeasts, fungi, and other organisms outside the bark cause the sap to ferment and develop a foul smell in which dogs like to roll. This makes your dog somewhat less pleasant to pet or allow into the house.

To minimize the foul smell, you can swab the area of trunk where the sap seeps out with a ten percent solution of chlorine bleach to kill the fermentation organisms. This will be a temporary solution to the problem and must be repeated as the odors redevelop.

The disease usually does not kill an otherwise healthy tree, but it does stress the tree. It may contribute to branch dieback and to the death of trees which are stressed by lack of water, winter injury, or other injury.

There is nothing you can do to cure the disease. An older recommendation is to "pipe" the trunk of infected trees by inserting a pipe through the bark of the tree. The intent of piping is to drain the gas pressure and the sap. Unfortunately, this procedure has proven to be more damaging than the slime-flux disease and is no longer recommended. You should take measures to keep the tree as vigorous a possible so that it may continue to grow in spite of the disease. This means you should provide adequate irrigation when needed and in the zone of absorbing roots. Absorbing roots are found from just inside the dripline of the tree outward to a distance from one to three or more times the height of the tree. The dripline is the ring of soil under the outer edge of the tree's branches. When nutrient deficiencies are indicated by soil testing or by symptoms in the tree, needed nutrients should be applied in this same region of absorptive roots in which water is applied. Prune out dead or injured branches, being careful to leave the branch collar, a slightly swollen area at the base of the branch being removed. Leaving the branch collar promotes more rapid wound closure and limits entry of decay organisms into the remaining portion of the tree.

As you noted, however, the sap oozing out can inhibit wound closure. Nevertheless, pruning paints are not needed. Since you are removing dead or severely injured branches, you can prune them any season of the year.

In time you may consider it wise to replace the tree. Plant a slower growing tree which is less susceptible to slime-flux. If you have sufficient space, you may wish to plant a slower growing tree now and as it becomes larger, remove the tree with slime-flux disease.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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