Ash Tree Diseases: Warning Signs of a Sick Tree

A photo of wilting leaves and potential dieback of an ash tree indication ash tree diseases

The beautiful and strong ash tree is dotted throughout England’s landscapes. It is not only loved by many, but also allows for the survival of thousands of species. With that being said, there are certain ash tree diseases and threats that may rampage the UK’s population of ash trees if not careful.

Being able to spot the warning signs of a sick ash tree could mean you can save it before irreparable damage is done, so if you’re lucky enough to have an ash tree in your garden, make sure to familiarise yourself with the below ash tree diseases and their warning signs. If you’ve got any concerns about the health of your ash tree, don’t hesitate to pick up the phone and give Treesaw a call on 0113 239 1271 – we’re dedicated to saving your trees and will do all we can to restore it to its former health.

Ash dieback disease (Chalara dieback of ash)

Known as ‘Chalara dieback of ash’ or simply ‘Ash dieback disease’, this ash tree disease is well known for the devastation it has caused in Europe. It is caused by a fungus called Hymenoscyphus fraxineus and will generally kill the tree that it infects (either directly or through weakening it to other diseases) other than in some rare cases which are being studied.

There are a number of symptoms that can indicate that your ash tree may be suffering from Ash dieback disease. An early and visibly sign is the thinning and dying of the top of your ash trees, along with wilting leaves and dieback. Dieback is characterised by the stalks turning brown or even black, accompanied by wilting and dying leaves. Another way to spot Chalara is by checking any blacked leaf stalks once they have fallen. You may spot fruiting, fungus-like bodies upon the stalk. This warning sign of the ash tree disease should absolutely prompt you to seek expert help.

Emerald ash borer (EAB)

Another well-known issue for ash trees is the Emerald ash borer (EAB), a larvae which feeds upon the tree beneath the bark, causing mass damage to the tree tissue. Although difficult to detect due to very few signs to begin with, there are some tell-tale warning signs that can be spotted if one is looking for them.

To begin with, the only warning signs that your ash tree is sick will be small cracks in the bark, just a few inches long. However, as time goes on and more and more larvae feed on the ash tree, other symptoms will follow such as your tree’s upper canopy thinning (though this is common for many ash tree diseases) and ‘suckering’ which is when the lower trunk of the ash tree sprouts many small green shoots to try to compensate for the thinning canopy.

In addition to the above symptoms, which can be caused by other ash tree diseases, the most sure warning sign of EAB is small D-shaped holes appearing on the bark. To begin with this will be at the top of the ash tree so difficult to spot, but will move downwards as more larvae are present. There are exit holes and the characteristic D-shape is directly linked to EAB.


There is much concern about what the above two tree illnesses could do to our ash tree population. Not only is it important to prevent the spread of these, but you should also be sure that any trees in your garden and near your property are healthy so as not to risk damage to people or property. If you spot any of these warning signs on an ash tree, it’s highly recommended you contact a professional to assess the situation for you. Once assessed, Treesaw can advise on the best course of action and will only ever fell a tree if it is the only possible course of action.

Contact Treesaw today if you have any concerns about your ash tree or any other trees you are worried about. Our friendly and knowledgeable staff can help.