Ash dieback disease is caused by the fungus Chalara fraxinea. The disease begins with the leaves wilting and turning black and then spreads. As the fungus grows into the tree it blocks the xylem vessels, which transport water in the trunk and branches, and the tree eventually dies. The disease has become entrenched across most of Europe, but it has only recently been confirmed in the UK. There are 80 million ash trees in Britain and over 100,000 seedlings/saplings have already been destroyed to try and control the disease. In Asia, ash trees are immune to the disease so it’s possible a treatment might be derived from them.
Answered by Luis Villazon.