Cytospora canker

Cytospora canker is a serious fungal disease caused by Cytospora leucosperma, which primarily targets the bark of woody plants. As a necrotrophic pathogen, it colonizes the inner bark and cambium, causing the tissue to die. This leads to the formation of sunken or flat cankers that can eventually girdle branches or entire trunks, cutting off the tree's vascular system.

The host range for this pathogen includes a wide variety of fruit trees, particularly stone fruits such as apricots, peaches, cherries, and plums, as well as pome fruits like apples and pears. Trees that are already stressed due to drought, winter injury, or poor pruning practices are significantly more susceptible to successful infection by the fungus.

Symptoms typically begin with a slight discoloration of the bark, which later turns reddish-brown. A diagnostic feature is the appearance of small, raised structures called pycnidia scattered across the surface of the cankered area. These structures release spores during wet weather. Over time, the bark may split, and the underlying wood becomes dark, dry, and necrotic.

Development and spread of Cytospora leucosperma are heavily influenced by environmental moisture. Spores are disseminated by splashing water, wind, and even contaminated pruning tools. The infection process is most successful when the tree's defense mechanisms are compromised, allowing the fungus to enter through wounds, cracks, or pruning scars during cool, moist periods of the year.

Management of the disease relies heavily on preventative cultural practices rather than curative chemical treatments.

• Prune out and destroy infected branches at least 6–8 inches below the visible canker.
• Sterilize pruning tools between cuts using alcohol or a bleach solution to prevent spreading spores.
• Avoid wounding the bark unnecessarily and protect trunks from winter sunscald.
• Ensure trees receive adequate irrigation and fertilization to maintain vigor.
• Provide optimal site conditions to reduce stress on the host trees.