Nectria Canker: Opportunistic Fungal Pathogen on Hardwoods

Nectria fruiting on a twig

Pathogen and Hosts

The fungus Nectria invades wood damaged by freezing, hail, animals, and insects. Most hardwoods with such injuries are susceptible. Slightly sunken cankers develop around wounds/damaged tissue. On smooth bark, cankers are darker brown than surrounding bark; on rough/dark bark, cankers are hard to see.

Nectria is an opportunistic pathogen attacking damaged wood. Active year-round when temperatures > freezing and sufficient moisture present. Trees weakened by recent transplanting, root pruning by excavation, and especially freezing are most susceptible. Autumn pruning in wet weather allows ready invasion. Vigorous trees usually form callus, wall off fungus within one year, and recover. Non-vigorous trees: invasion may continue, ultimately girdling/killing branch or trunk (small trees). Both asexual spores (conidia, all year) and sexual spores (ascospores, late summer) cause disease.

Symptoms and Signs

• Random branches/twigs fail to leaf out in spring.
• Branches of trees and trunks of small trees girdled and killed.
• Areas around wounds slightly sunken.
• Salmon, pink, or cream-colored fungal fruiting structures (small cushions) form in spring/early summer at cracks/natural openings in bark over canker. Turn brown/black with age, especially after freezing.
• Summer/fall: red to orange-red sexual fruiting structures form in cankered area.

Management

• Avoid injuring tree in autumn. Avoid autumn pruning, especially in wet weather.
• During dry weather, prune off infected branches.
• Protect trees transplanted within 2 years from drought and other stresses.
• Protect young trees from freeze damage where possible.