Ash dieback, caused by the fungus Hymenoscyphus fraxineus, has rapidly become one of the most serious threats to ash trees in the UK and across Europe.

Since its arrival in Britain in 2012, it has caused widespread damage, with experts predicting the potential loss of up to 80% of the country’s ash trees. This could have devastating consequences for wildlife, landscapes, and local ecosystems. Early detection is key to managing the spread and impact of this disease, so understanding how to spot the symptoms is vital.

1. What is Ash Dieback?

Ash dieback, also known as Chalara dieback of ash, is a fungal disease that primarily affects ash trees (Fraxinus excelsior), but can also infect related species. The disease disrupts the tree’s vascular system, hindering its ability to transport water and nutrients, which ultimately leads to the tree’s decline and death. The fungus spreads through spores released from infected leaf litter, which are carried by the wind, making it difficult to contain.

2. Recognising the Symptoms of Ash Dieback

Spotting the signs of ash dieback can be tricky, especially in its early stages. However, there are several key symptoms that you can look out for:

2.1 Leaf Discolouration and Wilting

One of the first visible signs of ash dieback is the wilting and discolouration of leaves. Infected leaves often:

• Turn black or brown at the tips and along the veins.
• Wilt or shrivel, despite no drought conditions.
• Drop prematurely, leading to early leaf fall during the growing season.

This can result in the tree looking unusually bare or sparse when it should be in full leaf, particularly during late summer or early autumn.

2.2 Shoot and Branch Dieback

As the disease progresses, it begins to kill off young shoots and branches:

• Shoot dieback: New growth will often die back from the tip, leaving dead, brittle ends.
• Lesions on branches: Dark, diamond-shaped lesions or cankers develop where the stem meets the base of leaves, often with the bark appearing sunken or cracked around the affected area.
• Branch dieback: Whole branches may die, particularly in the upper parts of the crown. This gives the tree a “stag-headed” appearance, where dead branches extend above living foliage.

2.3 Epicormic Growth

Trees suffering from ash dieback frequently produce epicormic shoots—new, bushy growth sprouting from the trunk or base of the tree. While this can initially look like healthy regrowth, it is actually a sign that the tree is under significant stress and is attempting to compensate for lost canopy.

2.4 Bark and Wood Damage

In more advanced cases, the disease causes further damage beneath the bark:

• Bark necrosis: Sections of bark may die off, particularly around lesions.
• Brittle wood: The internal wood can become brittle and more prone to breaking. This can compromise the structural integrity of the tree, making it dangerous in high-risk areas such as near roads or footpaths.

3. The Impact of Ash Dieback

Ash trees are a cornerstone species in many UK ecosystems. They support a wide range of wildlife, from birds and mammals to insects and fungi. As ash dieback spreads, it threatens not only individual trees but the entire ecosystem. The loss of mature ash trees could lead to a decline in species that depend on them for food and shelter. Additionally, the visual landscape of the British countryside, where ash is a common species, will be dramatically altered.

4. Why Early Detection is Important

Although there is no cure for ash dieback, spotting the disease early allows landowners and authorities to manage affected trees and potentially slow the spread. Some trees exhibit natural resistance, and early detection can help in monitoring these individuals for conservation and future breeding programmes. Managing infected trees by removing heavily diseased specimens can reduce the risk of falling branches in public spaces and may help to protect neighbouring healthy trees.

5. What to Do if You Suspect Ash Dieback

If you suspect ash dieback on trees in your area, it is important to report it to local forestry authorities or organisations such as the Forestry Commission. Avoid transporting leaves, wood, or soil from infected areas, as the fungal spores can spread easily through contaminated material.

6. Conclusion

Ash dieback is a serious and widespread threat to the UK’s ash population, but early identification can play a crucial role in managing its impact. By staying vigilant and learning how to recognise the signs of the disease—leaf discolouration, shoot and branch dieback, epicormic growth, and bark lesions—we can help mitigate the effects of this devastating disease. Protecting ash trees is not just about conserving a species, but also safeguarding the rich ecosystems that depend on them.