Valsa canker

Valsa canker, caused by the fungus Valsa ambiens, is a common and destructive disease that targets the bark and cambium layers of various woody plants. The pathogen thrives by invading wounded or stressed tissues, eventually leading to branch dieback and, in severe cases, the death of the entire tree.

This pathogen has a wide host range, frequently affecting pome and stone fruit trees, such as apple, pear, and cherry, as well as several ornamental species. Trees that are already weakened by unfavorable environmental factors, such as winter cold damage or drought stress, are significantly more susceptible to successful colonization by the fungus.

The clinical signs of the disease include the formation of sunken, discolored necrotic lesions on the bark. As the disease progresses, these areas become covered with small, pimple-like structures which are the fruiting bodies of the fungus. Affected branches typically exhibit yellowing of the leaves, followed by wilting and death during the growing season.

The development and spread of Valsa ambiens are highly dependent on high humidity and rainfall, which facilitate the dispersal of fungal spores. These spores are spread by water splashes, wind, and even human activity, such as pruning with non-sanitized tools, allowing the fungus to infect new hosts through the slightest bark opening.

Protection and prevention strategies are essential for maintaining a healthy orchard or landscape:

• Prune out and destroy all infected branches to reduce inoculum levels.
• Sterilize pruning tools using alcohol or bleach solutions between cuts.
• Apply wound dressings or tree paints to large pruning cuts and frost cracks.
• Improve tree vigor through proper irrigation, fertilization, and site management.
• Apply copper-based fungicides as a preventative measure during dormancy.