Cytospora canker

Cytospora canker is a serious fungal disease caused by various species of the Cytospora genus. It is categorized as a bark necrosis disease that primarily attacks the stems and branches of trees. In agriculture, this pathogen is recognized as a significant threat to tree health, often leading to dieback and the eventual death of affected specimens.

This fungus affects a wide range of fruit-bearing trees, including apple, pear, cherry, plum, and apricot, as well as various ornamental trees like willow and poplar. The disease is most opportunistic, targeting trees that have been weakened by environmental stressors, mechanical injuries, or inadequate maintenance practices.

The primary symptom of the disease is the appearance of sunken, reddish-brown areas on the bark. As the lesion expands, it may encircle the branch or trunk, cutting off the flow of water and nutrients, which results in the wilting and dying of the parts above the infection site. Small, pimple-like structures called pycnidia form on the surface, which exude spore masses under high humidity conditions.

Environmental conditions that favor the spread of Cytospora include high humidity, prolonged dampness, and temperatures conducive to fungal growth. The fungus enters the tree through wounds such as pruning cuts, insect damage, sunscald, or winter injuries. Once established, the mycelium penetrates deep into the bark tissues, making the infection difficult to eradicate once it reaches the vascular system.

Effective management and control rely on preventive measures, as there is no single curative treatment. Strategies include:

• Promoting tree vigor through proper irrigation and balanced fertilization.
• Pruning out and destroying infected branches, ensuring tools are disinfected between cuts.
• Protecting trunks from sunscald and winter injury using light-colored paint.
• Minimizing physical damage to the bark to reduce entry points for the pathogen.
• Applying copper-based fungicides as a preventative spray to protect vulnerable areas.