If one of your trees has a crack, wound, or other damage point that has begun to leak a thick, slimy, foul-smelling liquid, you are probably dealing with a common infection called slime flux. A slime flux infection usually enters a tree through wounds caused by insects, lawn mowers, bad pruning jobs, or nails from decorations, swings, and treehouses. Over time, the heartwood becomes discolored and the bacteria carry out fermentation and produce gases like carbon dioxide and methane. It is the building pressure of these gases that push liquid out through any available cracks and openings in the surface of the tree.
As infections go, slime flux is not rapid-acting or especially severe; it can even prevent the tree from picking up other types of fungal infections. However, it also attracts insects and yeast bacteria to feed on the oozing slime, which will become steadily more toxic and can sometimes start to eat into the surface of the tree. If other plants grow near the base of the tree, the slime can kill them. If the seeping continues beyond a few weeks or months, the overall health and growth of the tree can be stunted. Worse, if the tree is under stress in other ways, especially soil issues, the infection can cause a slow wilting and die-off of leaves and branches that may eventually kill the tree.
Slime flux cannot be cured, but it is manageable. If a tree in your yard is infected, you should seek an assessment by a qualified arborist, who may recommend one of a variety of treatments, such as surface disinfecting or cutting away the diseased branches or bark. Sometimes slime flux goes away by itself! Cleaning off the slime with a garden hose can help make the tree less attractive to yellow jackets and other insects. If the infection is too advanced, the arborist may advise you to have the tree removed.