Ash Dieback

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Ash dieback is a serious disease of ash trees caused by the fungus Hymenoscyphus fraxineus (It used to be called Chalara fraxinea). The disease causes leaf loss and crown dieback in affected trees and can lead to the death of the tree.

Ash dieback is no longer a regulated pest. It is present and widespread across Northern Ireland. Plant Health no longer survey for Ash Dieback or issue legal notices for the removal of infected trees.

Background

Ash dieback is caused by the fungus Hymenoscyphus fraxineus, First identified in Britain in 2012, research indicates it arrived earlier via imported nursery stock and airborne spores. The disease leads to leaf loss, crown dieback and bark lesions. The disease spreads more rapidly in humid, dense woodlands, while trees in open areas may deteriorate more slowly.

Biosecurity

There are things you can do to prevent pests and diseases spreading from site to site.

Want to help protect our trees? Find out what you can do with simple biosecurity

Management of Trees with Ash Dieback

Management strategies focus on safety, conservation, and biodiversity. Landowners are advised to assess tree health, remove hazardous trees, and retain tolerant specimens to support natural resistance.

The following guidance documents provide practical advice for tree owners, contractors, and local authorities.

Forestry Commission: Managing Ash Dieback in England: https://www.gov.uk/guidance/managing-ash-dieback-in-england

Arboricultural Association: Ash Dieback Guidance Note: https://www.trees.org.uk/Trees.org.uk/media/Trees-org.uk/Documents/eBooks/AshDieback-GuidanceNote-web.pdf

Tree Council: Guide for Tree Owners: https://treecouncil.org.uk/guidance-resources/ash-dieback-disease-a-guide-for-tree-owners/

LEAF (Linking Environment And Farming) A Farmers Guide to Ash Dieback-Leaf