Diagnosing and Managing Hypoxylon Canker in Oak Trees

Symptoms of Hypoxylon Canker

An oak in central Texas shows black, flaking bark at the base and brown leaves that have persisted for three weeks. The surrounding plants are healthy. These signs point to Hypoxylon canker, a fungal disease that attacks stressed oaks, especially after drought.

Disease Progression

The fungus causes branch dieback, yellowing and drying foliage, and eventually kills the tree over one or more years. As the tree dies, the outer bark sloughs off, revealing brown spore masses that later turn gray with black fruiting structures. The fungus enters through wounds and thrives at 86°F but can grow between 50–100°F.

Can the Tree Be Saved?

If leaves have fallen completely, the tree is dead. If brown leaves remain attached, the tree is still alive and needs immediate deep watering. Apply 1 inch of water every fourth day (use a pan under the sprinkler to measure). There is no chemical cure because the fungus lives inside the wood.

Prevention and Management

Maintain tree health to prevent infection: avoid trunk and root injuries, never add fill soil around the base, and water during droughts. If the tree dies, remove it promptly to reduce spore spread. Consider replacing with a more resistant species for your area.