Cankers of Hardwood Deciduous Trees: Types, Diagnosis, and Management

Understanding Cankers on Deciduous Woody Ornamentals

Cankers are localized areas of dead bark and underlying wood on twigs, branches, and trunks. They can be caused by living organisms (fungi, bacteria) or non-living factors (temperature extremes, hail). Many canker fungi normally inhabit tree surfaces, entering through natural/man-made wounds and causing disease only under stress. Some aggressively attack trees.

Three General Types of Cankers

1. Annual Cankers: Caused by fungi unable to cause disease unless tree is stressed/low vigor. Infection during host dormancy. Growing season callus walls off canker, preventing spread. Don't persist but continued stress = more cankers and worse diseases. Example: Fusarium canker.
2. Perennial Cankers: Seldom lethal but weaken structure and appearance. Fungi invade wounds/stubs during dormancy. Host forms callus during growing season; fungus invades more next dormancy. Interaction creates target-spot canker. Examples: Nectria canker, Eutypella canker.
3. Diffuse Cankers: Elongate with little/no callus. Fungus invasion so rapid that edge tissue killed quickly. Branches/whole trees girdled sometimes in single season. Often kill trees. Examples: Chestnut blight, Botryosphaeria canker, Phytophthora dieback, Cytospora canker.

Nursery Practices for Canker Prevention

Examine deciduous woody ornamentals for cankers. Prevent trunk/branch injury. Prune late in dormant season without damaging branch collar/bark. Prune small unwanted branches for quick healing. Don't prune during wet weather or mid-August to leaf drop (many canker/wood decay fungi most active then).

Promote Moderate Tree Vigor

Express natural resistance and prompt wound healing:

• Prevent drought and flooding
• Provide moderate fertilizer
• Prevent herbicide injury
• Prevent root/trunk injury
• Protect from insects/diseases causing premature leaf loss

Canker Inspection Checklist

When inspecting branches/young trees, look for:

1. Localized roughened/cracked bark, especially around wounds/branch stubs
2. Callus formation in multiple layers/ridges
3. Small pimple-like fungal spore structures in centers/edges of above (red, dark brown, or black depending on fungus)

If on branches: prune 3-4 inches below canker. Main trunk cankers on saplings = remove entire tree. Perennial/diffuse cankers persist for tree life and shorten it considerably. No chemicals adequately control canker-causing fungi.

Integrated Canker Management

The fundamental principle: canker fungi exploit stress. Prevention through vigor maintenance, wound prevention, and proper pruning timing is the only effective long-term strategy. Chemical control is inadequate. Early detection and prompt removal of affected branches (or entire trees for trunk cankers) limits spread and structural weakening.