Hazel rust

Systematic position and nature of the pathogen: Pucciniastrum coryli is an obligate parasitic fungus belonging to the phylum Basidiomycota, order Pucciniales. It is a specialized phytopathogen that causes hazel rust, affecting the foliage of hazelnut (Corylus spp.) and significantly impacting the photosynthetic capacity and vitality of the trees.

Symptoms and host plants: The primary host is the common hazel (Corylus avellana) and its cultivars used for commercial hazelnut production. The disease manifests as small yellow spots on the upper leaf surface, followed by the appearance of bright orange-brown pustules, known as uredinia, on the underside of the leaves. Severe infections lead to chlorosis and premature leaf drop.

Biology and life cycle: This fungus exhibits a complex, heteroecious life cycle. It often requires an alternate host, such as spruce (Picea), to complete its development stages and survive the winter. During the growing season, the pathogen spreads rapidly via urediniospores, which are dispersed by wind, leading to secondary infection cycles and widespread outbreaks within orchards.

Environmental conditions and impact: The development of rust is favored by warm, humid conditions, frequent dew, and high moisture levels during the growing season. The economic impact is linked to the loss of leaf surface area, which reduces nut yields, lowers oil content, and stresses the plant, making it more susceptible to frost damage and other opportunistic pathogens.

Protection and control measures: Effective management relies on a combination of cultural and chemical strategies.

• Sanitation through the removal and destruction of fallen leaves in autumn to reduce the inoculum load.
• Pruning to improve canopy airflow and reduce local humidity.
• Application of fungicides, such as copper-based products or systemic triazoles, during periods of high disease pressure.
• Establishing new orchards away from susceptible coniferous host species.