Mud flow is no cause for concern

There is a substance oozing from the trunk of my elm tree. What is it and what should I do to fix it?

—Jasmine Suarez, Skokie

Your tree appears to have slime flux, which is a very common bacterial disease that can occur in many types of trees, but is most common on elm in Illinois. It can also be found on trees such as oak, maple, redbud, sycamore, poplar, and cottonwood.

Slime flux, also called wet wood, is not normally a serious condition. However, a tree with a chronic case of wet wood may lose its overall vigor. The bacterium usually enters the tree through a wound, where it ferments and creates internal pressure.

Viscous flux initially appears as a dark brown to black water-soaked area in the wood. The moisture containing the bacteria will then drain from cracks, wounds or other weak areas of the tree trunk. The liquid is colorless or pale, while the inside of the tree darkens when exposed to air. When the liquid dries, it leaves a pale gray to white crust on the bark. A foul odor can sometimes develop due to decaying secondary organisms. Decay fungi do not thrive in waterlogged wood on the trunk.

There is no cure for slime flux, and in most healthy trees this disease is not considered a life-threatening problem for them. Trees should naturally compartmentalize an injured or diseased area without any intervention on your part.

Occasionally, a branch may die if fluid is transported through the tree’s vascular system. Prune the branch if this happens and sterilize your pruning tools between cuts to avoid spreading the disease. Provide your tree with extra water during dry periods and fertilize in the spring or fall to help reduce stress and improve tree vigor. There is not much you can do for your tree.

For more plant advice, contact the Chicago Botanic Garden’s Plant Information Service at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.