Alder catkin cup

Alder catkin cup is a fungal disease caused by the ascomycete Ciboria amentacea. This pathogen specifically targets the catkins (male inflorescences) of alder trees (Alnus species), acting as a parasite that interferes with the tree's reproductive processes.

The primary host plants for this fungus include common alder (Alnus glutinosa) and grey alder (Alnus incana). The pathogen affects the structural integrity of the catkins, leading to significant damage to the floral tissues and reducing the production of viable pollen and seeds, which directly impacts the forest regeneration potential.

Symptoms of the infection typically appear as browning, premature drying, and shriveling of the catkins. As the disease progresses, small, saucer-shaped fungal fruiting bodies known as apothecia develop from the infected tissue. These bodies are usually brown and supported by a distinct stalk, which facilitates the release of spores into the air.

The development and spread of Ciboria amentacea are heavily influenced by environmental conditions, particularly high humidity and moderate temperatures during the spring months. The fungus overwinters in mummified catkins or as sclerotia on the forest floor. When spring conditions arrive, the apothecia emerge to release ascospores that are carried by the wind to infect young, developing catkins.

Management and prevention measures are focused on reducing the spore load in sensitive areas such as forest nurseries or seed orchards. Recommended actions include:

• Removal and destruction of fallen catkins and infected debris.
• Monitoring of stands during early spring to identify outbreaks.
• Implementation of cultural practices to improve airflow and reduce humidity around seedlings.
• Use of certified, disease-free seed stock in reforestation projects.