Alder catkin hypertrophy

Alder catkin hypertrophy is a specific fungal disease caused by the ascomycete fungus Taphrina alni. This pathogen exclusively affects alder trees (Alnus species), leading to severe malformation of the male catkins, transforming them into conspicuous, elongated, and distorted galls.

The disease cycle begins with the fungus overwintering as spores on the tree's bark or within the bud scales. In early spring, these spores germinate and infect the developing catkins. The transmission of the fungus is primarily facilitated by wind currents and splashing raindrops during periods of high humidity.

The most visible symptom of the infection is the rapid proliferation of infected tissue, resulting in enlarged, thickened, and twisted structures that replace normal catkins. These growths often exhibit vibrant red or greenish-yellow colors as the fungus produces its spores on the surface of the deformed plant material.

Environmental conditions play a critical role in the development and spread of Taphrina alni. A wet and cool spring is particularly favorable for the disease, as these conditions support the rapid expansion of the mycelium and the efficient dispersal of conidia across the canopy.

The impact of this disease is mainly related to the biological sterilization of the infected parts, preventing seed production in affected catkins. While it rarely threatens the overall survival of mature trees, it significantly impacts reproductive success in localized populations. Management strategies focus on sanitation and monitoring of high-value landscape trees.