What is Ash Dieback.

Ash dieback, Hymenoscyphus fraxineus (also known as Chalara fraxinea)

It is the most significant tree disease to affect the UK since Dutch elm disease which was first recognised in the 1960s. It will lead to the decline and death of the majority of ash trees in Britain and has the potential to infect more than two billion ash trees1 (over 1.8 billion saplings and seedlings to more than 150 million mature trees) across the country.

Ash dieback, sometimes known as Chalara, affects ash and other Fraxinus species of trees and is caused by a fungal pathogen.

The fungus arrived from Asia to Europe during the 1990s and spread rapidly across Europe. Although the first official record in Britain was in 2012, evidence now suggests it arrived here earlier, with analysis demonstrating trees dying from the fungus in 2004.

This invasive fungus causes a range of symptoms from foliar leaf spots to branch dieback to the death of Fraxinus excelsior (ash) trees and some other Fraxinus species. Once infected, most trees will die. A few ash trees may survive the infection because of genetic factors which give them tolerance to the disease. In non-woodland situations, the percentage of the UK’s ash trees that are likely to be tolerant to the fungus is uncertain. In woodlands, evidence in December 2018 suggests mortality rates may be between 70% and 85%. Evidence from Europe suggests that around 10% of trees were found to be moderately tolerant to the disease, with 1-2% having high levels of tolerance. The environment also has a role in how trees decline from ash dieback, with trees growing outside of optimal conditions declining more quickly.


The precise speed of decline of any individual tree is currently impossible to predict and will be influenced by other factors including soil type, soil moisture levels and topography.

Forestry Commission are encouraging the industry and the public to remain vigilant for signs of Ash Dieback on new tree and shrub species and report suspected sightings through its reporting system: https://www.treecheck.net/

A strategic and co-ordinated local response is required to deal with the multiple issues that ash dieback presents.

The national cost of removing trees with ash dieback is difficult to calculate but the health and safety implications of affected roadside trees will require significant investment.

The scale of health and safety risks caused by ash dieback alone will mean that it will not be ‘business as usual’ for any organisation managing ash trees.


Should you, or your organisation require assistance with this then please get in touch, we will be happy to help and advise.