Valsa canker of willow

Valsa canker, caused by the fungus Valsa salicina, is a common and destructive bark disease affecting willow trees. As a facultative pathogen, it primarily targets stressed or damaged trees, leading to localized tissue necrosis and potential death of branches or entire trunks if left untreated.

The fungus affects various Salix species, particularly those growing under unfavorable conditions such as waterlogging, drought, or poor soil fertility. Entry points typically include pruning wounds, insect feeding sites, winter injury, or any physical damage that exposes the inner bark tissues to infection.

Early symptoms include bark discoloration and minor cracking. As the disease progresses, the infected area becomes sunken, and the bark may eventually peel off. A hallmark of this disease is the development of small, erumpent fruiting bodies of the fungus, which release spores that can further spread the infection during humid weather.

Environmental factors play a crucial role in disease development. Valsa salicina thrives in moist environments, where sporulation and dissemination are most active. Warm, humid spells during the growing season facilitate the rapid spread of conidia via splashing rain, wind currents, and contaminated pruning equipment.

Effective management requires an integrated approach. The primary defense is the removal and destruction of infected wood to reduce the inoculum load. Maintaining tree vigor through proper fertilization, adequate watering during droughts, and careful pruning techniques can significantly decrease the susceptibility of willow trees to Valsa canker.

• Prompt removal of infected branches
• Sterilization of pruning tools between cuts
• Application of copper-based fungicides on major wounds
• Avoiding mechanical damage to tree bark