If you have noticed sap oozing, sometimes frothy, down the side of your trees they may be suffering with slime flux.

Occasionally maples, elm, oak, birch, and a few other shade trees can develop a wetwood disease. Tree owners first notice a vertical streak of wet bark on the trunk beginning at a crack or wound up on the trunk and extending all the way to the ground. This seepage is often accompanied by discoloration of the bark where the water flows. Sometimes this flow becomes foul-smelling indicating an associated product called slime flux. 

The quick explanation of what has happened is that bacteria have infected the heartwood and inner sapwood of the tree. The waste produced by the bacteria, namely methane and metabolic liquids, starts to build up pressure until they are forced out the nearest available opening, usually a trunk wound or pruning cut. As the fluid runs down the tree, it is fed on by fungi, yeasts, and bacteria until it changes to a brown, slimy ooze. 

Wetwood disease does not appear to directly harm the tree but it does not go away and can be an additional stress to the tree over time. So far there are no effective preventive or curative controls.

Source: Kelly Jackson, Horticulture Agent for Christian County