Paul Pecknold, Extension Plant Pathologist
During growth, trees can become infected with bacteria that inhabit the wood and cause a condition known as wetwood or slime flux. The bacteria infect trees through wounds caused by impact, pruning, or cracks from freezing or weak limb crotches. The bacteria may live within the tree for many years without any outward evidence that the tree is infected. Eventually gasses produced by the bacteria can cause the internal pressure of the sap to become very high.
As a result of high sap pressure, the sap oozes out of openings in the bark and runs down the trunk of the tree, causing dark streaks that then turn light gray or white upon drying. Oozing sap may be frothy at the point of exit. Airborne bacteria, yeasts, and fungi often colonize the wet oozing material, called slime flux, which it to ferment and smell very bad. Slime flux may delay wound healing (callus formation).
There are many trees in the Midwest that may develop slime flux. It is extremely common on elms; in fact, the majority of elms in Indiana have slime flux as a chronic condition. Slime flux is common on oaks and mulberry, and it may infrequently occur on maples (including box elder), paper birch, butternut, redbud, sycamore, and walnut.
There is no control for slime flux. Inserting a drain tube into the tree to relieve pressure and drain infected sap was once an accepted treatment of trees with slime flux. This procedure is not recommended; it may do more harm than good. Boring holes in affected trees causes internal spread of the bacteria within the tree and allows entry of wood decay fungi.
Prevention consists of proper pruning of branches to allow rapid and sound healing; preventing other wounds to the trunk, branches, and roots is also important. Compacting soil around roots or disturbing root zones by installing flower beds around the base of trees creates wounds through which the bacteria can enter. Proper fertilization helps to invigorate affected trees.
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