Willow rust

The disease is caused by the pathogenic fungus Melampsora epiphylla, a member of the basidiomycete group. This fungus is a specialized parasite that primarily affects the foliage of willow species (genus Salix). It interferes with the plant's metabolic processes by hijacking nutrients from living cells to support its own development.

This pathogen poses a significant threat in nurseries, forest plantations, and urban landscapes where willow trees are planted in high density. The disease is particularly damaging to young, vigorous saplings, as it directly impacts their ability to synthesize energy and maintain optimal growth rates throughout the season.

The primary symptom of infection is the emergence of bright orange to yellowish uredinia (spore pustules) on the abaxial side of the leaves. As the infection progresses, these pustules can cause the leaf tissue to necroticize, turn brown, and eventually trigger premature leaf abscission. Heavy infestations lead to significant canopy thinning.

High humidity, moderate temperatures, and frequent rainfall are critical factors that drive the spread and germination of Melampsora epiphylla spores. Wind is the main agent for long-distance dispersal. The fungus typically overwinters in the mycelial or spore form within leaf litter and debris, providing a constant reservoir of infection.

Managing this fungal disease requires a combination of sanitation and chemical interventions to maintain plant health:

• Rigorous sanitation by removing and destroying fallen leaves in autumn to disrupt the life cycle.
• Implementing proper spacing to ensure adequate air circulation and reduce micro-humidity in the canopy.
• Applying preventive fungicides or systemic treatments during periods of high infection risk.
• Prioritizing the planting of resistant cultivars and maintaining overall plant vigor through balanced fertilization.