Understanding Ash Dieback: A Growing Threat to the UK’s Native Trees

Ash dieback is a devastating disease affecting ash trees—particularly the UK’s native species, common ash (Fraxinus excelsior). Also known as Chalara dieback, this condition is caused by the aggressive fungus Hymenoscyphus fraxineus (H. fraxineus), which poses a serious and growing threat to ash populations across the country.

Originally from East Asia, this invasive pathogen has spread rapidly through Europe. It attacks the tree’s vascular system, interrupting the flow of water and nutrients. This disruption gradually weakens the tree and, in many cases, leads to its death.

Given its wide-reaching impact on our native landscape, spotting the early signs of ash dieback is crucial—for tree preservation, public safety, and biodiversity.

How to Spot Ash Dieback: 5 Key Warning Signs

If you have ash trees on your land, it’s vital to monitor them for signs of infection. Here are the most common symptoms to look out for:

1. Crown Dieback

A clear sign of ash dieback is the gradual deterioration of the tree’s crown. The disease usually begins at the top of the tree, where leaves may wilt and discolour before spreading downwards. Over time, affected branches die back, leading to a sparse and unhealthy canopy.

2. Diamond-Shaped Bark Lesions

Look for distinctive lesions on the bark—often diamond-shaped—that appear on the trunk or branches. These marks are caused by the fungus damaging the tissue beneath the bark and are a reliable visual clue of infection.

3. Epicormic Growth

As a last-ditch effort to survive, infected ash trees may produce epicormic shoots—new growth that sprouts unusually low on the trunk or main limbs. While this might appear to be a sign of recovery, it’s actually a stress response indicating the tree is under attack.

4. Discoloured or Prematurely Fallen Leaves

Leaves affected by the disease often show dark patches or blotches, and may fall off well before autumn. The resulting thinning canopy reduces the tree’s ability to photosynthesise, accelerating its decline.

5. Branch Cankers and Dead Tissue

The disease causes cankers—areas of dead bark and tissue—on the branches. These cankers disrupt the flow of sap and compromise the tree’s structure, making it more susceptible to breakage or collapse.

The Importance of Early Detection and Timely Action

Regular inspections are key to managing the risk of ash dieback. If you suspect that a tree may be affected, it’s essential to act quickly. Early diagnosis can help limit the spread to surrounding trees and improve the chances of salvaging part of the tree’s structure.

Where appropriate, strategic pruning or removal of infected limbs can slow the disease’s progress and reduce the risk to nearby healthy trees.

Speak to the Tree Care Professionals

At The Original Tree Surgeons, we bring over 40 years of hands-on experience in caring for trees and managing landscapes. We offer free consultations to assess any suspected cases of ash dieback and advise you on the best course of action.

Our fully qualified arborists stay at the forefront of tree disease management, with up-to-date knowledge on treatments, regulations, and best practices for containing infections.

Whether it’s a single tree or a large estate, we can create a tailored plan to manage the issue effectively—protecting both your property and the wider environment.

If you have any questions or are worried about a tree on your property, talk to us today: 020 8088 5202

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