Poplar catkin leaf curl

The causative agent of this disease is the fungus Taphrina johansonii, a member of the Taphrinaceae family. This pathogen is highly specialized, specifically targeting the reproductive structures of trees within the genus Populus. It is a distinct fungal disease that significantly alters the development of catkins without affecting the tree's foliage or trunk health.

The primary hosts for this fungus include various species of poplar, such as the trembling aspen and the white poplar. The pathogen induces hypertrophy and hyperplasia in the tissues of the catkins. Because of this focus on reproductive organs, the disease is primarily observed during the early spring months when these trees are flowering.

Symptoms become apparent as the catkins emerge. Infected catkins grow abnormally large, become distorted in shape, and often take on a distinct yellow or orange hue. The surface of these deformed catkins is covered with a powdery substance, which is actually a dense layer of fungal asci ready to release spores into the environment.

The development of Taphrina johansonii is strongly influenced by cool, wet spring weather. High humidity and mild temperatures during bud break facilitate the infection process as spores land on susceptible developing tissues. The pathogen survives the winter in the form of dormant spores or mycelium located on bud scales or bark fissures, waiting for the right conditions to activate.

The economic and ecological impact of this disease is linked to the sterilization of affected catkins, which prevents the production of viable seeds. While not lethal to the tree, it affects seed production cycles. Recommended management strategies include:

• Pruning and destroying infected branches if economically feasible.
• Applying copper-based fungicidal sprays during the dormant season.
• Monitoring nursery stock for signs of infection in early spring.
• Promoting healthy growing conditions to improve general tree vigor.