Ash dieback will affect the majority of ash trees in the UK. The disease arrived in the UK in 2012 and has since spread across the country, weakening ash trees to the point that they will drop limbs, collapse or fall.
The disease is caused by a fungus which blocks water transport in the tree, leading to scratches in the bark, leaf loss and eventually killing the tree from the outermost branches inward. The economic cost of the disease to the UK is predicted to reach up to £15 billion.