European Ash Tree Diseases: Warning Signs of a Sick Tree

An image of a Eurpoean ash tree affected by dieback of ash.

Ash trees can grow up to 35m tall and are often found together. European ash trees have many distinct features, but unlike other trees are known for their leaves falling whilst still green. Unfortunately, there is a real threat to ash trees known as Chalara dieback of ash, causing the tree to lose their leaves and the graceful crown of the tree to die back.

The prevalent disease is caused by a fungus called Hymenoscyphus fraxineus and in April 2018, scientists grew increasingly concerned at the rate by which European ash trees were being killed. It is estimated that dieback threatens 95% of all European ash trees and has already damaged or killed a quarter of the trees in southern Sweedon. In addition to this, the tree disease has destroyed more than 80% of ash trees in Norway.

Ash Dieback Warning Signs

If you’re concerned about ash dieback affecting your trees, there are three key signs you should look out for.


Should your tree be affected, black blotches will often appear at the base of the leaf, and at midrib. Additionally, affected leaves will often wilt.


The disease will display itself on stems by small lens-shaped lesions or necrotic spots on the bark on stems of branches – these may enlarge to form perennial cankers. In some cases, the infection can kill a stem in a single season.

The Whole of the Tree

When looking at the entirety of a tree affected with ash dieback, the tree will show various dead shoots, twigs and branches. Affected trees often also have prolific epicormic shoots.

Treatment of Ash Dieback Disease

There is no chemical control of this ash tree disease available, but where individuals suspect that a tree may be suffering from ash dieback, they should report it to a health authority. If you should suspect that your tree is suffering from dieback, it is important that you seek advice on how to deal with leaf litter, before putting it into your compost bin.

Other Ash Tree Diseases

Dieback of ash may also occur as a result wood decay fungi and by the root pathogen, honey fungus. However, this fungi can also affect trees which are already suffering from Hymenoscyphus fraxineus.

Treesaw Tree Surgeons

Unfortunately, trees that suffer from Chalara dieback of ash (Hymenoscyphus fraxineus) will typically die from the disease. If you would like a tree removed or cut back from your garden, we welcome you to contact our specialist team. We judge each case individually to ensure the tree receives the most appropriate course of action. Call us today on 0113 239 1271 or send your enquiry through to our online contact form.