Ash dieback

Ash dieback is a serious fungal disease caused by the ascomycete Hymenoscyphus fraxineus. This pathogen targets the vascular tissues and bark of ash trees, causing systemic necrosis that effectively chokes off the plant's ability to circulate sap and nutrients.

The disease primarily affects Fraxinus species, with the European ash (Fraxinus excelsior) being the most susceptible. It is a highly destructive pathogen that has caused massive mortality rates in ash populations across Europe, posing a significant ecological and economic threat to timber production and urban forestry.

Key symptoms include the wilting and premature shedding of foliage, browning of leaf stalks, and characteristic diamond-shaped lesions on the bark of stems and branches. As the disease advances, trees exhibit crown thinning, stunted growth, and the eventual death of the entire canopy, leading to tree failure.

The life cycle of the fungus is heavily dependent on environmental conditions, particularly high humidity and moderate temperatures during the summer months. Spores are released from small, white fruiting bodies found on fallen leaf petioles from the previous year and are subsequently spread via wind currents over long distances.

Current management strategies focus on preventing the spread of the pathogen by regulating the movement of nursery stock and infected wood products. Since there is no curative fungicide available for large-scale use, the primary focus is on identifying and breeding genetically resistant ash trees and implementing sound silvicultural practices to manage infected stands.