Willow leaf rust

The disease is caused by the pathogenic fungus Melampsora salicis-albae, which belongs to the Basidiomycota phylum. This fungus is a specialized parasite that targets the foliage of willow trees, completing its biological cycle through the production of various spore types, often including urediniospores that allow for rapid spread during the growing season.

The primary hosts of this pathogen are various Salix species, including Salix alba. It is particularly problematic in commercial willow plantations, nurseries, and ornamental landscaping, where the integrity of the foliage is essential for both the tree's health and its visual appeal.

Visible symptoms include the development of bright yellow or orange pustules on the undersides of leaves, which are the fungal fruiting bodies. As the season progresses, these structures turn dark brown or black, resulting in premature leaf necrosis, leaf yellowing, and early defoliation, which hampers the tree's ability to store energy for the winter.

The spread of the disease is heavily influenced by environmental factors such as high humidity, frequent rainfall, and moderate temperatures. Under these conditions, the fungal spores are effectively disseminated by wind and water splashing, leading to rapid infection cycles within dense willow populations.

The economic and biological damage caused by Melampsora salicis-albae is significant, as it severely impacts photosynthesis and carbohydrate reserves. Repeated annual infections can stunt tree growth, reduce the biomass of short-rotation willow crops, and ultimately lead to the decline or death of sensitive tree specimens.

• Remove and destroy all fallen leaves during autumn to reduce inoculum.
• Ensure adequate spacing between trees to improve air circulation.
• Apply preventative fungicides specifically labeled for rust control.
• Maintain tree vigor through proper irrigation and balanced fertilization.
• Select and plant willow varieties that have known resistance to rust.