Slime flux, also known as bacterial wetwood, is a condition resulting from a bacterial infection that causes fermentation and oozing in a tree’s internal tissues. This problem occurs when anaerobic bacteria colonize the water-soaked wood, leading to gas and fluid buildup. The pressure from this internal fermentation forces the toxic, foul-smelling liquid out through cracks and wounds in the bark. This article provides practical guidance on how to diagnose this issue and implement effective management strategies to support your tree’s health.
Understanding Slime Flux and Its Origin
Slime flux originates from wetwood, where the tree’s internal wood becomes saturated and colonized by common soil and water-inhabiting bacteria. These bacteria thrive in the low-oxygen, or anaerobic, environment of the water-soaked wood, where they ferment carbohydrates within the tree’s sap. This metabolic activity produces gases, including methane and hydrogen, which generate significant internal pressure, sometimes reaching up to 60 pounds per square inch (psi) in the trunk.
This pressure forces the fermented, discolored sap to flux out of the trunk through weak points like pruning cuts, branch crotches, or bark cracks. The visual symptom is a wet, dark streak running vertically down the bark, which often dries to a pale gray or white crust. The most characteristic sign is the odor, which is often sour, alcoholic, or distinctly fermented due to the microbial activity within the ooze.
Common host trees susceptible to this condition include elms, cottonwoods, poplars, oaks, maples, and willows. The bacteria typically gain entry through any open wound, even small ones caused by insects, frost cracks, or careless lawn equipment. While the wetwood itself is generally chronic and rarely fatal, the constant acidic ooze prevents the wound from closing properly, increasing the tree’s vulnerability to decay fungi and other secondary pathogens.
Immediate Steps for Managing the Active Flux
The first immediate step in managing active slime flux is to address the exposed ooze, which is toxic to the living tissue, or cambium, it contacts. Gently wash the area with a mild solution of water and soap, or a very dilute bleach solution, to remove the flux and prevent further bark damage and staining. This surface cleaning also discourages insects like bees and wasps, which are attracted to the fermented fluid.
In the past, a common practice was to drill a hole below the flux site and insert a drain tube to relieve the internal pressure. However, this method is no longer widely recommended by arborists because it creates a new, deep wound that can break the tree’s natural compartmentalization barrier. Drilling can inadvertently spread the infection within the wood and introduce wood-decay fungi, ultimately causing more harm than good.
The infection itself is internal, residing in the water-soaked wood, making external chemical treatments ineffective. Applying fungicides, antibiotics, or wound dressings is generally not helpful, as these substances cannot reach the bacteria deep inside the tree’s structure. Focus instead on supporting the tree’s natural defense mechanisms, allowing it to seal off the affected area.
If loose or obviously diseased bark surrounds the flux point, carefully remove only the discolored tissue down to the healthy, yellow-green cambium. This action helps the tree form a clean wound margin, which facilitates the compartmentalization process. Always sterilize pruning tools, such as with 70% rubbing alcohol, between cuts to avoid spreading the bacteria to other parts of the tree or to other plants.
Long-Term Strategies for Tree Health and Recovery
Since there is no “cure” for the internal bacterial wetwood, the most effective long-term strategy involves improving the tree’s overall health to enable it to isolate the issue. Maintaining high tree vigor is the primary defense, as a healthy tree can effectively wall off the infected wood. Stress reduction is paramount, considering that factors like drought, poor soil, or mechanical damage often precede the onset of wetwood.
Proper watering is a foundational practice, especially during dry periods, to mitigate drought stress. Provide deep, slow irrigation that moistens the entire root zone, rather than shallow, frequent watering. Avoiding root zone saturation is equally important; ensure the soil drains well and consider amending heavy clay soils with organic matter to improve aeration.
Correct soil management involves applying a two- to four-inch layer of organic mulch over the root zone, keeping it several inches away from the trunk flare. This helps to conserve moisture, regulate soil temperature, and prevent trunk injury from lawnmowers or string trimmers, which create entry points for the bacteria. Pruning should focus on removing dead, weak, or broken branches, as these are common entry sites for the infection.
Knowing When to Call an Arborist
While most cases of slime flux are chronic but not immediately life-threatening, certain signs indicate the need for professional intervention. You should contact a certified arborist if the active flux continues unabated or worsens despite your management efforts over a growing season. A professional can provide an accurate diagnosis and assess the extent of the internal damage.
Concerns about the tree’s structural integrity require immediate attention. If the infection is widespread, affecting multiple large branches or covering more than half of the trunk circumference, the tree may be structurally compromised. An arborist can evaluate the safety risk and determine if advanced techniques like decay testing are necessary.
Structural Integrity Concerns
The flux may be associated with large cracks, significant branch dieback, or advanced wood decay.
General Decline
General decline, such as extensive wilting, premature leaf drop, or scorch in the canopy, suggests the wetwood is impacting the tree’s vascular function.
If you are unsure about the cause of the oozing or if other concurrent issues are present, a professional diagnosis is the best course of action. They can develop a comprehensive long-term care plan focused on maximizing the tree’s natural defenses.