Valsa canker

Valsa canker, caused by fungi of the Valsa genus (often associated with Cytospora), is a serious disease impacting various fruit and ornamental trees. This pathogen primarily affects the inner bark and cambium layers. As the infection progresses, it prevents nutrient transport, causing the branches to wilt and die, which can eventually lead to the loss of the entire tree.

A wide range of crops is susceptible to this infection, most notably apples, pears, peaches, cherries, and plums. The fungus acts as a wound parasite, entering the plant through damage such as pruning cuts, sunscald, or winter frost cracks. Trees suffering from poor site conditions, drought stress, or mechanical damage are particularly vulnerable to colonization by this pathogen.

The primary symptom of the disease is the appearance of localized, sunken, or discolored lesions on the bark. As the canker expands, the affected bark may become soft or spongy. In later stages, small, pimple-like fruiting structures appear on the bark surface. In moist conditions, these structures release spores that may emerge in thin, gelatinous, orange or yellow tendrils.

Disease development is highly favored by high humidity and the presence of wounds on the tree's surface. The fungus overwinters in the mycelial form within infected tissues, such as dead twigs or canker margins. Spores are primarily dispersed during rain events, as water splashes the spores onto nearby susceptible tissues or open wounds during the spring and early summer.

Effective disease management strategies involve the following practices:

• Strict sanitation by pruning out and destroying all infected wood.
• Disinfecting pruning tools between cuts to prevent mechanical transmission.
• Maintaining tree vigor through proper fertilization, watering, and soil management.
• Preventing sunscald and winter injury by painting trunks with white latex paint.
• Applying preventive copper-based fungicide sprays during dormant or early budding stages.