Ash dieback is caused by the Chalara fraxinea fungus. The fungus causes leaf loss and crown dieback and can lead to tree death.
It is not known how the disease spreads, but it could be by insects or rain splash, over longer distances it is believed to be transferred by the movement of infected trees.
Symptoms of Chalara fraxinea can be visible on leaves, shoots and branches of affected trees and include:
- In severe cases, the entire crown shows leaf loss and dieback
- There may be the formation of dormant shoots under the bark on branches and the trunk
- Foliage Leaves can suffer from wilting and black-brownish discoloration
Experts say little can be done to stop the spread of 'Ash dieback' the disease threatening to devastate the UK's ash trees.
One of the UK's biggest tree growers will seek damages from the government after losing thousands of trees to ash dieback disease.
The disease threatening to wipe out the majority of Britain's ash trees may have spread - as experts say an import ban was too slow.