Cytospora canker

The disease is caused by the fungus Cytospora mali (the sexual stage is known as Valsa mali). It is a persistent fungal infection that primarily affects the bark and cambium layer of fruit trees. By disrupting the tree's vascular system, the pathogen causes localized necrosis, which leads to branch dieback and eventually the decline of the entire tree.

While commonly referred to as a disease of apple trees, Cytospora mali has a wide host range, including pear, plum, cherry, and other rosaceous trees. The fungus behaves as a weak parasite, primarily invading trees that are stressed due to drought, frost injury, sunscald, or improper maintenance practices that leave open wounds.

Early symptoms include the appearance of sunken, reddish-brown patches on the bark. As the lesion matures, the bark becomes dark and often shows small, pinhead-sized pimples known as pycnidia. During periods of high humidity, yellowish or orange spore tendrils may extrude from these structures. Unlike other canker diseases, the tissue under the affected bark often becomes spongy and separates easily from the underlying wood.

The spread of the disease is highly dependent on environmental moisture. Spores are disseminated by rain splash, wind, and even insect activity. The fungus enters the tree through any breach in the bark, such as pruning cuts, cracks from cold weather, or damage caused by pests. The disease can be active throughout the growing season, particularly when temperatures are moderate to warm.

Managing Cytospora canker requires diligent sanitation and stress reduction. Effective measures include:

• removing and burning infected branches well below the margin of the visible canker;
• disinfecting pruning tools between cuts to prevent cross-contamination;
• maintaining tree vigor through proper irrigation and balanced fertilization;
• protecting tree trunks with whitewash to prevent sunscald;
• applying copper-based fungicides during the dormant season and early spring to protect susceptible areas.