Hypoxylon Canker on Water Oak: Post-Flood Stress and What You Can Do

Diagnosis

Black, rusty-bordered canker (1.5 ft × 8 in) in fork of lowest major branch on 40-ft water oak. Appeared after Hurricane Rita (2 weeks standing water, 4 months mud/debris). This is Hypoxylon canker.

Key Facts

• Attacks stressed trees (flooding, fill soil, drought, wounds).
• Causes dark brown sapwood discoloration; older wood shows black zones in cross-section.
• No known cure.

Management

• Prevention: Water/fertilize properly (especially during drought), avoid soil compaction and wounds.
• Deadwood: Fungus remains active; burn infected wood promptly to limit spore spread.
• Fertilize now: Apply 13-13-13 in spring from 2 ft out to drip line.

Reality Check

Tree may decline over years. Focus on supporting vitality and preventing spread to other oaks.