- 12th December 2020 -

Spotting and tackling ash dieback symptoms

Spotting and tackling ash dieback symptoms

The first step in tackling tree diseases such as ash dieback is to recognise its presence. Spotting ash dieback symptoms early can limit the damage to your healthy trees and slow the spread of this devastating fungus.

With its smooth grey bark and distinctive black buds, the ash tree is a popular sight across the UK. Sadly, it’s future is under threat from a disease which is predicted to wipe out the majority of ashes in the country: ash dieback disease.

Understanding ash dieback disease

Ash dieback disease is caused by the fungus Hymenoscyphus fraxineus. Carried on the wind, the spores of this slow-spreading but relentless and deadly disease settle on and penetrate the leaves of most species of ash tree. The fungus then grows within the tree’s transport system, blocking the delivery of vital nutrients. 

Few trees have any immunity to the fungus and young ashes are often killed very quickly. Older trees can survive for several seasons before dying, often due to the effects of additional diseases.

For more detailed information about the origin and spread of ash dieback, see our dedicated article on the disease.

So what are the tell-tale symptoms of ash dieback disease?

Leaf discolouration and wilting

One of the most distinctive symptoms of ash dieback disease are branches of blackened and wilted leaves in the height of summer. These dead leaves will often be shed early.

In earlier stages of the disease, the leaves will start to show blackened patches, particularly around the base and midrib.

Lesions and cankers

Large necrotic lesions (wounds surrounded by dead tissue) are another typical symptom of ash dieback disease. These affect the bark and underlying tissues and are often found where the tree’s branches meet its trunk. Lesions are dark brown in colour and a distinctive diamond or lens shape. Peeling back bark will often reveal brown-grey discolouration on the inside too.

You may also find lesions elsewhere on the bark of branches or stems. These can grow to become perennial cankers. In some cases, cankers can encircle a stem, cutting off its nutrient supply and causing it to die within a single season.

Dieback and epicoral growth

Since the fungus grows within the ash’s transport system, it will block essential nutrients leading to the death of leaves, shoots, twigs and branches. This is particularly noticeable in the summer months where you will observe significant crown dieback.

A typical response to stress in trees is a spurt of epicoral growth. This is where previously dormant buds near the bottom of the tree burst into life. This is another key symptom of ash dieback disease.

Evidence of secondary pests and diseases

While ash dieback disease can kill young trees very quickly, older trees often struggle on for many years. Weakened by the fungus, they invariably become susceptible to a host of other diseases and opportunistic pests. 
These include Neonectria ditissima, the fungus responsible for apple canker; pseudomonas savastanoi, a plant-attacking bacteria and the ash bud moth which carves out stems and damages buds in May.

What can you do about ash dieback on your land?

While there is currently no physical or chemical treatment that can save infected ash trees, there are ways to slow the spread and potentially save trees that have yet to be infected.

Diseased trees should be felled as they can provide a danger to the public. Leaves should be either carefully collected and burnt or buried under four inches of soil or six to twelve inches of other organic material. This will stop the fungus from creating new spores.

Arborcure can help by carrying out tree felling, commercial land clearance and, where necessary, re-planting.


If your ash trees are displaying any of the above symptoms, get in touch with Arborcure. We can confirm whether you have ash dieback disease or not and help you manage the outbreak.

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