Tree Diseases

Tree Pests: Diseases

Stinky Slime Flux on Broadleaf Trees

This problem is not always as bad as it appears

Do you have a tree that seems to be leaking a smelly liquid? Arborists call that smelly liquid slime flux, which is usually seen in the heat of summer on the trunk, large limbs or basal roots mostly on oaks, maples and elms. Slime flux is most common on large, older trees and in spite of its smell is to some extent beneficial to the tree.

Notice the typical persistant wet stain caused by a slime flux infection.

Notice the typical persistant wet stain caused by a slime flux infection.

Slime flux is caused by a condition inside the tree called wetwood, which is caused when bacteria invade a wound or injury. The bacteria cause fermentation and produce methane gas, not unlike the process that follows when you eat a bean burrito for lunch. The methane gas creates pressure and pushes the bacteria-laden liquid out openings such as the old wound or a narrow crotch with embedded bark. The liquid is odorless inside the tree but takes on a foul smell when it reaches the air outside and is colonized by yeast-like fungi and other organisms. Wasps and hornets often are found feeding on the fermenting slime.
Slime flux will not kill a tree but is merely a sign that there has been an earlier injury. In some cases as the outer wound calluses over and the internal methane production decreases, the slime flux may stop in a year or two. In other cases slime flux may reoccur year after year.
Curiously, wetwood and the associated slime flux help protect the infected tree. The bacterial growth creates conditions in the wood and slime that inhibit wood decay organisms. Furthermore, if the slime flux continues to flow over a number of years, the liquid that is toxic to other organisms can discolor the bark, kill moss and lichens on the bark and even kill grass at the base of the tree. The stain on the bark can be either light or dark color.

There is no treatment for slime flux but that fact may not stop insistent garden center sales clerks from selling homeowners “a cure” anyway. In the past arborists would insert a tube in the tree to allow the slime flux to flow more freely and drip onto the ground. But this technique is no longer recommended because it doesn’t improve the problem and the hole for the tube is just one more injury to the tree.

If the smell becomes annoying because a slime fluxing tree is near a door, window or patio, a homeowner can hose off the slime from time to time with water or even occasionally spray a dilute solution of bleach on the slime to temporarily inhibit the congregating insects and reduce the smell.