Hazelnut phyllosticta leaf spot

Systematic position and type of pathogen. Phyllosticta coryli is a pathogenic fungus belonging to the genus Phyllosticta within the Ascomycota division. It functions as an obligate or facultative parasite that specializes in invading the leaf tissues of hazelnut trees, disrupting their physiological functions.

Diseases and host crops. This pathogen is the primary cause of phyllosticta leaf spot, a fungal disease that affects various species of the Corylus genus, including commercial hazelnut orchards. While it primarily manifests on leaves, the infection can sometimes occur on young succulent stems under high disease pressure.

Biology and life cycle. The fungus overwinters in fallen leaves as pycnidia, which are specialized fungal fruiting bodies. In early spring, under warm and wet conditions, the pycnidia release conidia that are disseminated by rain splash or wind. Throughout the growing season, the pathogen completes multiple cycles of infection, spreading rapidly within the canopy of the host plants.

Conditions for development and harmfulness. Disease development is favored by high humidity, prolonged rainfall, and poor air circulation within the orchard. The primary damage is the necrosis of leaf tissue, which inhibits photosynthesis. This reduction in the plant's metabolic capacity leads to weakened vegetative growth, stunted nut development, and potential yield losses in commercial production.

Protection and control measures. Management of Phyllosticta coryli requires a proactive approach. Cultural practices such as the removal and destruction of leaf litter at the end of the season are critical to reducing the primary inoculum. Pruning to maintain adequate tree spacing and airflow is also essential. In orchards with a history of the disease, targeted applications of copper-based or systemic fungicides during the early leaf-development stages can effectively mitigate the spread.