Blister canker

Blister canker, also known as nailhead canker, is a fungal disease caused by Biscogniauxia marginata. It is a wood-decaying pathogen that invades the bark and cambium layers of woody plants, leading to severe localized necrosis and long-term structural decline of the host tree.

The primary host for this fungus is the apple tree. It typically colonizes trees that are already suffering from physiological stress, drought, nutritional deficiencies, or extensive wounds from pruning. Older, poorly maintained orchards are significantly more susceptible to this infection compared to well-managed ones.

Diagnostic symptoms include the formation of irregular, sunken areas on the bark. As the disease progresses, the fungal stroma pushes through the bark surface, appearing as small, black, circular structures that resemble the heads of nails. This is accompanied by the cracking of the bark and the eventual death of affected branches.

The development of the disease is highly dependent on humidity and temperature. Spores are released during wet weather and can enter the tree through natural openings or mechanical wounds. Once established, the fungus grows slowly within the wood, often remaining latent before producing visible fruiting bodies on the tree surface.

Management of the disease focuses primarily on prevention and sanitation. It is essential to prune and burn infected branches, ensuring that all tools are sterilized between cuts to prevent cross-contamination. Maintaining healthy trees through optimal irrigation, balanced fertilization, and avoiding unnecessary bark injuries are the most effective ways to mitigate the risk of severe infection.