Bacterial Wetwood Slime Flux

If you see an oozing, slimy discharge streaming down elm trunks (especially in spring and summer), that's slime flux from bacterial wetwood. The dark, foul-smelling flux stains bark and can accumulate at branch crotches or pruning wounds, creating an unsightly mess. On American elm, European elm, and other species common to landscaping here, this visible drainage is the main symptom you'll notice; the affected wood inside remains wet and discolored but doesn't necessarily kill the tree quickly.

Bacterial wetwood is difficult to eliminate once established because the bacteria live inside healthy-looking wood. Your best approach is prevention: avoid wounding trees through thoughtful pruning, keeping mower equipment clear of the trunk, and careful handling. If flux is already appearing and bothering you aesthetically, you can install plastic drain tubes to direct the fluid down the trunk to the ground rather than across the bark. Prune out severely affected branches if necessary, but accept that the condition is chronic and generally won't kill the tree outright.