Ash dieback

Ash dieback is a devastating fungal disease caused by the pathogen Hymenoscyphus fraxineus. This disease causes necrosis in the stems, branches, and leaves of ash trees, eventually leading to the death of the entire tree.

The primary host for this fungus is the European ash (Fraxinus excelsior), although other ash species can also be affected. The disease has spread across much of Europe, causing significant ecological damage to native woodlands and affecting urban tree populations.

Visible symptoms include wilting and blackening of leaves during the summer months, followed by premature leaf fall. Lesions often develop on the bark, appearing as diamond-shaped necrotic patches around the base of twigs or branches. When these lesions encircle the branch, they cut off the sap flow, causing the tip to die off and creating the characteristic "dieback" appearance.

The fungus spreads via wind-borne spores produced on the rachises of fallen leaves from the previous year's infection. High humidity and mild temperatures during the summer create ideal conditions for spore release and infection, allowing the fungus to rapidly colonize new host trees.

The economic and ecological impact of ash dieback is severe, as it leads to the loss of biodiversity and the destruction of mature timber. Current management strategies focus on identifying and breeding disease-resistant genotypes of ash. Furthermore, forest management practices emphasize avoiding the transport of infected plant material and removing deadwood in high-risk areas to reduce local inoculum pressure.