Black Sap Oozing from Tree: Slime Flux (Wetwood)

What Is Slime Flux?

Dark, frothy, foul-smelling sap bleeding from bark cracks or wounds indicates slime flux, the external symptom of wetwood—a bacterial infection in the heartwood. Common in many hardwoods.

Causes and Symptoms

• Bacteria enter through wounds, pruning cuts, or root injuries.
• Microbial fermentation produces gas pressure, forcing sap out.
• Sap is alkaline, killing grass/plants below; dries to gray-white crust.
• Internally, wood is water-soaked, dark, and malodorous.

Management

• No cure exists. Drain tubes are no longer recommended—they spread bacteria and invite decay fungi.
• Prune dead/dying branches.
• Fertilize to boost vigor and wound closure.
• Avoid unnecessary wounds; use clean pruning tools.
• Prevent moisture stress with proper watering.

Outlook

Trees can live for years with slime flux. It's a chronic condition, not an immediate death sentence.