White neonectria

White neonectria (Neonectria candida) is a fungal pathogen responsible for necrotic and canker-like diseases in various woody plants. This fungus acts as a parasite that primarily attacks the bark and cambium layers, disrupting the tree's vascular system and causing significant physiological stress to the host.

The disease affects a variety of broadleaf trees and shrubs, including common orchard species and ornamental cultivars. Susceptible trees often include those already compromised by environmental stressors such as frost cracks, sunscald, pruning wounds, or existing insect damage, which facilitate the initial entry of the fungus into the plant tissues.

The most prominent sign of an infection is the emergence of white, cushion-like sporulating structures on the surface of the infected bark. As the pathogen colonizes the bark, it causes localized necrosis, which leads to cracked, sunken, and often discolored areas. If left unmanaged, these lesions expand into deep cankers, eventually girdling the branch or stem, which leads to canopy dieback.

The development of Neonectria candida is heavily dependent on moisture and humidity. High humidity levels combined with moderate temperatures provide ideal conditions for sporulation and subsequent infection of the host. Spores are primarily dispersed through wind, rain splashes, and sometimes through mechanical transmission during pruning activities, with the fungus overwintering as mycelium in the dead tissue.

Management strategies focus on reducing inoculum load and enhancing tree vitality to prevent successful colonization. Key protection measures include:

• Pruning and immediate removal of all symptomatic branches, ensuring cuts are made into healthy, living wood.
• Sanitizing pruning tools with alcohol or bleach between trees to prevent cross-contamination.
• Applying copper-based fungicides as a preventative measure during dormancy.
• Promoting overall plant vigor through proper fertilization, watering, and soil management.