Swollen Bark on Oak Trees: Canker Disease Explained

A homeowner in southern Louisiana notices swollen, splitting areas on the bark of multiple oaks, forming round centers. The description points to a canker disease—a fungal infection that kills bark tissue.

What Are Cankers?

Cankers are localized dead areas on branches or trunks caused by fungi entering through wounds or stressed tissue. Over 20 canker-causing fungi exist in North America. They form fruiting bodies that release spores, spreading the infection.

Types of Cankers

• Target cankers: Concentric rings of callus tissue form over years, creating a bull's-eye pattern.
• Diffuse cankers: Oval, sunken or swollen lesions with little callus; they girdle branches quickly.

Predisposing Factors

Drought, nutrient deficiency, insect defoliation, herbicide injury, and root damage weaken trees, making them susceptible. Young, suppressed, or poorly sited trees are most vulnerable.

Next Steps

1. Review the Cornell fact sheet on canker diseases: plantclinic.cornell.edu.
2. If uncertainty remains, email clear photos to jimhyland@yahoo.com for further identification.
3. Maintain tree vigor: water during drought, fertilize appropriately, and avoid wounding trunks.

Cankers rarely kill mature oaks outright but can weaken structure over time. Monitoring and cultural care are key.