Ash dieback

Ash dieback, caused by the fungus Hymenoscyphus fraxineus, is a devastating disease affecting ash tree species. It is widely recognized as a major threat to both natural forests and urban landscapes, leading to severe crown thinning and eventual tree mortality across many regions.

The causal agent is an ascomycete fungus that infects the leaves and spreads to the twigs and branches. It colonizes the xylem, causing necrotic lesions in the bark and wood tissue. This disruption of the vascular system prevents the tree from transporting water and nutrients, resulting in rapid physiological decline.

Symptoms typically manifest as wilting of foliage, discolored necrotic lesions on the bark, and the death of twigs and lateral shoots. As the disease progresses, a thinning canopy becomes apparent, often accompanied by epicormic growth (shoots emerging from the trunk), which is a classic stress response of the dying tree.

The disease cycle is heavily influenced by environmental conditions, particularly humidity and temperature. Spores are released from small, white mushroom-like fruiting bodies that develop on fallen ash leaf petioles from the previous year. High rainfall and moderate temperatures during the growing season significantly enhance spore dispersal.

Effective management and prevention strategies include the following approaches:

• Removal and proper disposal of heavily infected timber to reduce local spore load.
• Sanitary pruning of affected branches in the early stages of disease progression.
• Implementing forest management practices that avoid dense monocultures to improve air circulation.
• Prioritizing the selection and breeding of resistant ash genotypes for sustainable reforestation efforts.