Bacterial wetwood is common to many Colorado shade trees, including willows, aspens, cottonwoods, elms and affects the inner core of the tree.
Symptoms of bacterial wetwood are a discoloration of the wood (usually yellowish), wet-looking bark and sometimes a slimy, foamy white ooze that smells similar to beer. This slimy ooze may seep through pruning cuts or cracks in the wood and has an off odor from yeast fermentation in the open air. As the ooze dries, it often leaves behind a white crust on the bark of the tree. In addition, the bacterium becomes pressurized within the trunk increasing the potential for additional oozing.
The slime is toxic to the cambium of the tree and any living plant tissue it touches (including weeds or leaves that come in contact with the slime). Fortunately, bacterial wetwood doesn’t really alter the strength of the wood but it can cause wood to warp and split after harvest. The means of entry for bacteria is likely through root wounds, pruning cuts and/or injuries from string trimmers and lawnmowers.
There is no cure for a tree diagnosed with bacterial wetwood; prevention is key. Drought may increase wetwood problems, so it’s very important to provide adequate water for trees throughout the year—including fall and winter. Trees may also benefit from additional fertilizer if nutrient deficiencies are apparent. Drain tubes are not recommended, as they provide another wound opening for bacteria to enter.
The odor from the slimy ooze may attract insects such as flies and beetles but they will not harm the tree or transmit the bacteria so control is not necessary. For more information, see CSU Extension fact sheet #2.910 “Bacterial Wetwood.”