Nectria canker

Nectria canker is a destructive fungal disease caused by various species of the Nectria genus, primarily Nectria galligena. The fungus acts as a wound parasite, meaning it infects trees through breaks in the bark caused by pruning cuts, insect damage, frost cracks, or even leaf scars. The infection affects the cambium layer, leading to the development of sunken lesions on stems and branches.

The disease primarily targets deciduous trees, showing high susceptibility in apple and pear orchards. It is also frequently found on ash, beech, and cherry trees. In environments with poor air circulation or overcrowding, the pathogen can spread rapidly through entire orchards, significantly reducing crop yields and causing the premature death of branches or entire trees.

Early symptoms include small, slightly sunken, dark-colored areas on the bark. As the canker progresses, the bark may crack, and distinct concentric callus tissue often forms around the site of the infection. The most diagnostic sign of the disease is the presence of clusters of small, bright red or orange fungal fruiting bodies (perithecia) appearing in the affected bark during cool, wet conditions.

Development and spread are favored by prolonged periods of rain and humidity, particularly during the dormant season and early spring. The fungus relies on water to disperse its spores, which can be splashed onto healthy bark or transported by wind. If an orchard is neglected or trees are stressed by adverse growing conditions, the disease can become entrenched and difficult to manage.

Management of Nectria canker requires a strict integrated approach:

• Pruning out and removing all visible cankers during dry weather.
• Disinfecting pruning tools with bleach or alcohol to prevent cross-contamination.
• Applying protective wound sealants to major pruning cuts.
• Scheduling copper-based fungicide applications in autumn and spring.
• Improving tree vigor through balanced fertilization and proper irrigation.