Invasive plants and tree disease
Ash dieback: how to tell if your tree has it and what to do
Ash dieback is a fungal disease that kills ash trees, causing leaf loss, dark stem lesions and progressive crown thinning. Most infected ash trees decline over years and many die. A dying ash near a road, path or building can become brittle and dangerous, so badly affected trees should be assessed by a qualified tree surgeon.
- Also known as
- Hymenoscyphus fraxineus, Chalara dieback of ash, Chalara fraxinea
- Easily confused with
- drought stress, other ash pests and diseases, frost damage to new growth
- How serious
- High for affected trees: progressive decline and a real safety risk
- Typical cost
- Inspection and works vary widely with tree size and access; expect a survey fee plus felling or reduction costs
How to identify ash dieback
Forest Research describes the typical signs: blackened, wilting leaves in summer, dark brown or orange-brown lesions (often diamond shaped) on stems and branches where they meet the leaf, and dead shoots.
Over time the crown thins and dies back from the top and outer branches, and the tree may produce clumps of new shoots (epicormic growth) lower down as it struggles. Saplings can be killed quickly, while mature trees usually decline over several years. The Woodland Trust and Forest Research provide identification guidance and photos.
How serious is it?
High for affected trees: progressive decline and a real safety risk
Ash dieback is a serious tree disease. Forest Research notes it affects ash trees across the country and that many infected trees will die, with the disease well established in the UK.
For homeowners the main concern is safety. As an ash declines it can become brittle and shed limbs or fail, so a diseased ash near a road, footpath, building or boundary needs assessment, and you have a duty of care for trees on your land that could harm people or property.
How to fix it yourself
- Confirm the signs using Forest Research and Woodland Trust guidance: summer leaf wilting and blackening, diamond-shaped stem lesions, and crown dieback from the top.
- Monitor the tree over the season and keep notes and photographs of how quickly it is declining.
- Do not attempt to fell or heavily prune a sizeable ash yourself, as diseased ash becomes brittle and unpredictable, making it dangerous to climb or cut.
- Keep people and parking away from a clearly failing tree until it has been assessed.
- Check current gov.uk and Forest Research guidance, as advice on reporting and managing ash dieback is updated over time.
When to call a professional
- Any sizeable or declining ash near a road, path, building, boundary or where people pass.
- When you are unsure how advanced the disease is, or whether the tree can be retained, reduced or needs felling.
Who to call
- An Arboricultural Association (ARB Approved) tree surgeon or a qualified arborist for inspection and any felling or pruning.
- Your local council tree officer if the tree is near a road or public area, or covered by a Tree Preservation Order or conservation area rules.
Indicative cost: Inspection and works vary widely with tree size and access; expect a survey fee plus felling or reduction costs. Prices vary by area, severity and access, so always get a written quote.
Frequently asked questions
How can I tell if my ash tree has ash dieback?
Look for blackened, wilting leaves in summer, dark diamond-shaped lesions where branches meet the stem, dead shoots, and a crown that thins and dies back from the top. Forest Research and the Woodland Trust provide photographs to help confirm it.
Do I have to fell a tree with ash dieback?
Not always. Some affected trees can be retained or reduced, especially away from where people pass. But a declining ash near a road, path or building can become brittle and dangerous, so a qualified arborist should assess whether it can be kept, reduced or needs felling.
Is ash dieback dangerous to humans?
The fungus itself does not harm people. The risk is indirect: a dying ash becomes brittle and can shed limbs or fail, so a diseased ash near where people walk, park or live is a safety concern that should be professionally assessed.
Who is responsible for a diseased ash tree?
The landowner generally has a duty of care for trees on their land that could harm people or property. If your ash shows dieback near a road, boundary or building, you should arrange an inspection. Trees may also be protected, so check with your council tree officer before works.
Sources
Editor, HomesAndHedge
Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.
Last reviewed: 8 June 2026