Nectria Canker

Pathogen and disease type. Nectria canker, caused by the fungus Nectria haematococca, is a significant bark-necrosis disease. It is a parasitic fungus that enters host plants through wounds, pruning cuts, or environmental damage, compromising the vascular system and eventually leading to localized cell death in the bark and underlying sapwood.

Host range. The pathogen is known for its wide host range, affecting both economically important woody plants and decorative species. Notable hosts include hazelnut, black walnut, apple trees, and raspberries. It also impacts ornamental plants such as Exacum affine, Gerbera jamesonii, plane trees, and sweet gum (Liquidambar).

Symptoms and signs of infection. The primary symptom is the appearance of sunken, discolored, or reddish-brown lesions on the bark. As the infection progresses, the bark cracks, resulting in distinct open cankers. During moist conditions, the diagnostic sign is the formation of small, orange to red fruiting bodies (perithecia) on the surface of the infected areas.

Development and impact. The fungus thrives in cool, wet environments, which favor spore production and dispersal. Spores are primarily spread by wind and water splash. The economic impact is severe, as the disease can girdle stems and branches, leading to dieback, reduced yield, and, in severe cases, the complete death of the host plant.

Control and prevention measures. Managing Nectria canker requires a combination of cultural and chemical practices. Key strategies include:

• Pruning and removing infected branches, ensuring cuts are made into healthy tissue.
• Sterilizing pruning tools between cuts to prevent cross-contamination.
• Applying wound dressings or sealants to large pruning cuts to protect against spore entry.
• Utilizing copper-based fungicides during dormant or early growth stages.
• Maintaining plant vigor through proper fertilization and stress reduction.