Birch witches broom

The causative agent of this disease is the ascomycete fungus Taphrina betulina, which specifically targets birch trees. This pathogen induces hyperplastic growth in the host, leading to the formation of dense, abnormal masses of twig development known as «witches brooms».

Symptoms of the infection include the appearance of tangled, stunted, and numerous shoots growing from a single point on a branch. Leaves on these clusters are typically smaller, chlorotic or reddened, brittle, and often drop prematurely, significantly affecting the tree's overall canopy health.

Environmental conditions conducive to the spread of the fungus include cool and humid spring weather. Fungal spores are disseminated by wind and splashing rain, landing on healthy buds. Once established, the mycelium overwinters inside the dormant buds and initiates abnormal cell growth when the tree begins its seasonal growth cycle.

The impact of the disease is detrimental to tree vigor, causing metabolic stress and depleting the tree's nutrient reserves. Over time, heavy infestation can reduce the tree’s resistance to other environmental stressors, resulting in diminished growth rates, reduced vitality, and potential dieback of major branches.

Management strategies focus on containment and sanitation to minimize the fungal load in the landscape:

• Pruning and removal of all symptomatic branch clusters during the dormant season.
• Ensuring cuts are made well into healthy wood to remove internal mycelial infections.
• Disinfecting pruning tools with alcohol or bleach solutions between trees to prevent cross-contamination.
• Proper disposal of infected material, preferably by burning, to eliminate spore sources.
• Applying preventive copper-based fungicide sprays in early spring before bud break.