Brown leaf spot of willow

Drepanopeziza castagnei is a parasitic fungus responsible for the development of brown leaf spot disease on willow (Salix) species. As an ascomycete pathogen, it primarily attacks the foliage, causing premature defoliation and hindering the overall photosynthetic capability of the host plant, which is critical for tree growth.

This disease affects numerous willow cultivars, being particularly problematic in nurseries, gardens, and along water bodies where moisture levels remain high for extended periods. It can significantly impact the health of decorative landscaping and commercial wood production sites if left unmanaged.

The primary clinical signs of the disease are small, circular or irregular brown spots appearing on the leaves. As the infection progresses, these spots coalesce, leading to severe necrosis, chlorosis, and eventual drop of leaves. In some cases, the fungal structures may be visible as minute, raised bumps on the surface of the infected leaf tissue.

The development of the fungus is heavily influenced by climate conditions, specifically high humidity and moderate temperatures. Spores are disseminated through wind and water splashes during wet weather, facilitating the transition from fallen, overwintering debris to new leaf growth in early spring and throughout the growing season.

Effective control strategies focus on integrated management, including:

• Sanitation: Raking and burning or composting infected fallen leaves to remove overwintering inoculum.
• Cultural practices: Pruning branches to improve airflow and reduce humidity levels within the canopy.
• Chemical control: Utilizing systemic or contact fungicides during the early leaf expansion phase to prevent initial infections.
• Monitoring: Early detection during damp spells is essential to prevent large-scale outbreaks.

Managing the disease requires vigilance, as the fungal spores are resilient and can persist in the environment for years. By combining strict sanitation with timely chemical applications, it is possible to successfully suppress Drepanopeziza castagnei and maintain the vigor of affected willow trees.