Slime spotted on trees is known as bacterial ooze. There are different types of bacterial ooze, and they’re not very well studied. Bacterial ooze can easily go unnoticed. At its most basic they form when a tree gets damaged and subsequently infected with bacteria. In certain circumstances if the bacteria is able to feed on the tree sap and nothing prevents it from multiplying it will eventually form this slime.
Trees, like all plants, have an immune system which should protect them from severe infections like this. Bacterial ooze happens when the tree is unable to heal a wound and prevent the bacteria from feeding on the sap. Bacterial oozes are often fatal; the ooze that forms will rot the tree as the bacteria ‘eats’ it, ultimately leading to the tree’s death.
Without knowing what bacteria is causing the problem, it’s difficult to know how contagious an ooze might be, but in most cases the ooze itself only forms when specific conditions occur on a tree so shouldn’t spread in a woodland. The bacteria involved are often present in a woodland anyway without causing any problems – the ooze forms when something goes wrong and the bacteria breeds out of control.
Bacterial oozes may be accompanied by other pathogens that further harm the tree. For example, slime flux is a type of bacterial ooze that is a mix of bacteria and yeast. It has quite a distinctive orange/yellow appearance. The yeast and bacteria ferment the tree sap, leading to an unpleasant smell and attracting insects to the ooze.
How We Could Help
If you spot a tree with bacterial ooze on it, we recommend that you call Hometown Tree Experts to assess. Hometown Tree Experts would assess your tree to ensure that it is indeed safe as the rot may be weakening your tree. This issue may be spreading bacterial oozes to other trees on property so would advise assessment to prevent. If you are able to provide good photos we would appreciate this photo being emailed to us as we’d love to see them!
Common Types of Bacterial Ooze
The most frequent form seen on Maryland trees is bacterial wetwood, also called slime flux. It appears as dark, wet streaks running down the trunk from a wound, branch crotch, or old pruning cut, often with a sour smell. Wetwood develops when bacteria ferment sap inside the trunk and the pressure pushes the fluid out through cracks. Oaks, elms, maples, and poplars are commonly affected. While the staining looks alarming, wetwood itself is usually a chronic condition that a vigorous tree can live with for many years.
Management and Prevention
There is no cure that eliminates the bacteria, so care focuses on keeping the tree strong and limiting new wounds. Do not bore holes or insert drain tubes into the trunk, an old practice that creates fresh injuries and tends to make matters worse. Instead, support the tree with proper watering during drought, a healthy mulch ring, and pruning only with clean, sharp tools at the right time of year. If oozing is paired with dieback, cracking bark, or thinning canopy, the tree may have a more serious underlying problem that deserves a professional look.
If you spot persistent ooze or decline on a tree, our arborists can diagnose it. Call Hometown Tree Experts at 301-250-1033 or see our tree disease and treatment service. Clear photos emailed ahead of a visit help us prepare.