Valsa canker of paulownia

Valsa canker, caused by the fungus Valsa paulowniae, is a destructive bark disease that primarily attacks the stems and branches of paulownia trees. It is a major concern for silviculture, as it severely damages the vascular system, often leading to the economic failure of timber plantations.

The primary hosts for this pathogen are species within the Paulownia genus. While healthy trees possess some natural defenses, those subjected to drought, frost damage, or nutrient deficiencies become highly susceptible to colonization by the fungus.

Visible signs of the infection include sunken, discolored lesions on the bark, which gradually expand as the fungus kills the cambium layer. Over time, the bark may crack, and the underlying wood often exhibits signs of decay. Small, pimple-like fruiting bodies (pycnidia) eventually erupt through the outer bark, releasing fungal spores.

The development and spread of Valsa paulowniae are heavily dependent on environmental humidity and temperature. Spores are primarily dispersed through rainwater splashes and wind, entering the tree through pruning wounds, frost cracks, or sites damaged by sunscald, making proper wound management essential.

The impact of this disease is significant, as it leads to reduced timber quality, stunted development, and eventual tree death if not managed. Preventive measures focus on maintaining vigorous tree health through adequate irrigation and fertilization, practicing strict sanitation by removing diseased wood, and protecting wounds with fungicidal pastes or sealants.