The observation of a tree “leaking water,” appearing as dripping, oozing, or a sticky residue, signals a release of internal fluid. This liquid is typically sap, a sugary waste product called honeydew, or a bacterial exudate. The presence of this weeping material is a clear indication that the tree’s internal systems are actively engaged in circulation, defense, or response to external factors. Identifying the source is the first step in determining if the tree is undergoing a natural process or experiencing a health issue requiring intervention. This guide differentiates between non-threatening natural functions and leaks caused by insect activity or bacterial infections.
Healthy Tree Function That Causes Weeping
Not all external moisture indicates a problem; some weeping is a normal physiological process. One common cause is the natural flow of sap, often seen in “bleeder” trees like maple, birch, and walnut. This phenomenon is most noticeable following late-winter or early-spring pruning cuts when internal pressure is high and sap moves actively from the roots upward. The resulting liquid is usually clear and slightly sticky, and the flow subsides once the tree enters full leaf-out.
Another process, known as guttation, is sometimes mistaken for a leak, although it occurs primarily on leaves. Guttation involves the expulsion of excess water and dissolved minerals through specialized pores called hydathodes, typically found at the tips or margins of leaves. This happens when the soil is moist and the air is humid, causing root pressure to build up overnight because the plant’s normal daytime evaporation rate, called transpiration, is greatly reduced. The resultant droplets are often visible in the early morning.
Identifying Leaks Caused by Insect Activity
A sticky liquid coating leaves, branches, or surfaces beneath the canopy is frequently “honeydew,” the sugary waste excreted by piercing-sucking insects. Pests such as aphids, scale insects, and whiteflies feed by penetrating the tree’s phloem and extracting sap, which is rich in sugar but low in other nutrients. Because they ingest large volumes of sap to obtain sufficient protein, they excrete the excess sugar as a clear, sticky liquid that drips onto surfaces below.
The most distinctive sign of honeydew is the subsequent development of sooty mold, a black, non-parasitic fungus that grows exclusively on this residue. The mold does not infect the tree tissue but can block sunlight from reaching the leaves, interfering with photosynthesis. Another form of insect-related weeping involves boring insects. Their larvae tunnel under the bark and push out frass, a sawdust-like material mixed with sap, which often accumulates near small entry or exit holes on the trunk or branches.
Bacterial Infections and Slime Flux
A more serious cause of liquid discharge is Bacterial Wetwood, commonly referred to as Slime Flux, a chronic bacterial infection of the inner wood. This condition occurs when bacteria enter the tree through wounds and begin to ferment the internal sap. The fermentation process releases gases like methane and nitrogen, which build up significant internal pressure, sometimes exceeding 60 pounds per square inch.
This pressure forces the fermented, contaminated sap out through cracks, pruning cuts, or weak points in the bark. The liquid that oozes out, the “slime flux,” is highly acidic and often has a distinct, foul odor, frequently described as sour, alcoholic, or sewage-like. As the liquid dries, it leaves a characteristic dark, vertical streak on the bark, sometimes turning a foamy white or brownish-rust color. While rarely lethal to mature trees, it can cause localized bark dieback, prevent wound closure, and indicate an underlying stressor that compromised the tree’s natural defenses.
Determining the Cause and When to Call an Arborist
A simple diagnostic checklist can help identify the cause of the weeping by focusing on location, texture, and smell. Sap flow and slime flux are generally concentrated on the trunk or large branches, while honeydew is spread across leaves and surfaces below. Pure sap is clear and mildly sticky, honeydew is intensely sticky and often accompanied by black sooty mold, and slime flux is slimy, discolored, and has a pungent, fermented odor.
If the liquid is clear and the tree appears healthy, basic maintenance to reduce stress is usually sufficient, as the weeping will likely resolve itself. However, a professional arborist should be consulted if the tree exhibits a rapid decline in health, such as significant leaf loss or dieback in the crown, or if a large volume of liquid consistently weeps from the trunk. An arborist is also necessary if the oozing liquid is foul-smelling, indicating an active bacterial infection, or if the leak is accompanied by large structural wounds or significant frass, suggesting a severe borer infestation.