Black Bark on Oaks and Maples: Slime Flux Explained

Diagnosis

Blackened bark with ants but healthy green canopy indicates slime flux (wetwood)—a bacterial infection causing dark, frothy, foul-smelling sap to bleed from cracks and wounds.

Key Points

• Bacteria enter through wounds; ferment internally, producing gas pressure that forces sap out.
• Sap is alkaline, kills grass below, dries to gray crust.
• Internal wood is water-soaked, dark, smelly.
• No cure; drain tubes outdated and harmful.

Management

• Prune dead branches.
• Fertilize to improve vigor (10-10-10 at 1 lb/inch trunk diameter).
• Avoid wounding; use clean tools.
• Prevent moisture stress.

Outlook

Trees can live decades with slime flux. It's chronic, not acutely fatal.