Ash dieback is a fungal disease that kills the leaves, shoots and eventually the branches of ash trees. Many infected trees decline slowly, but once large limbs die the wood becomes brittle, so an ash near a house, road or path should be checked and either monitored, pruned or felled before it becomes a hazard.
7 minute readUpdated October 2026Last updated:
Look for leaves wilting and blackening in summer and diamond-shaped marks on the bark.
Not every infected ash needs felling; some keep much of their crown for years.
Dead ash wood becomes brittle, which makes later work harder and riskier.
Protected tree and nesting bird checks still apply to a diseased ash.
What ash dieback is
Ash dieback is caused by a fungus that arrived in Britain and has spread widely through native ash. Spores are carried on the wind from fallen leaf stalks in late summer, land on the leaves and grow into the shoots, blocking the tree's water transport. Year by year the crown thins as more twigs and branches die back from the tips.
Ash is one of the commonest trees in East Anglian hedgerows, field margins and older gardens, so most people with a mature tree on or near their land will meet the disease at some point. Some trees show a degree of tolerance, which is one reason a blanket approach of felling every ash is not recommended.
Signs in the canopy, bark and leaves
The easiest time to judge an ash is in mid to late summer, when the crown should be fully in leaf. Compare it with a healthy ash nearby if you can.
Leaves that wilt, turn black and hang on the shoots
Bare twig tips and a crown that looks thin or patchy
Diamond-shaped dark lesions where side shoots meet a branch
Clusters of new shoots sprouting low on the trunk or main limbs
Dead branches that stay bare when the rest of the tree leafs up
When an infected ash becomes a safety risk
A thinning crown on its own is a disease problem, not necessarily a safety problem. The risk rises when large branches die, because dead ash dries out and snaps more easily than many other species. Fungal decay at the base or in the roots is another warning sign, and can leave a tree that looks partly green but has a weak anchor.
What matters most is what lies underneath. An infected ash in the middle of a field can often be left to decline. The same tree overhanging a house, a drive, a public path or a road is different, because a falling limb could hurt someone or cause damage. If you are worried about a tree that has already split or dropped a large branch, the 24/7 emergency tree works page explains how to get it made safe.
Monitor, prune or fell
For a tree with mild symptoms and nothing important beneath it, monitoring once or twice a year is often enough. Note how much of the crown is affected and photograph it from the same spot each summer so changes are easy to see.
Where a few limbs have died over a garden or path, removing that deadwood can reduce the risk and buy time, while leaving the living crown to keep growing. When most of the crown has gone, or the base is decaying, felling is usually the safer answer. It is better done while the wood is still reasonably sound, because brittle trees are harder to climb and dismantle. Our tree surgery page covers how Craig plans felling and reductions, and the tree removal cost guide explains what drives the price.
Timing, nesting birds and permissions
Unless a tree is an immediate danger, plan the work around nesting birds, which are protected while active. Spring and early summer are the busiest months, so check carefully before cutting at that time of year.
Disease does not automatically remove legal protection. If the ash has a tree preservation order or stands in a conservation area, the local council may still need notice or an application before work, though there are exceptions for trees that are dead or dangerous. Our guide to tree preservation orders explains how to check and what to send.
Replanting after an ash is removed
Losing a large ash can open up a garden or a hedge line dramatically. Many people choose to replant with a different native species so the gap fills again over time. Think about the eventual size of the new tree, how close it will be to buildings and drains, and whether the stump of the old ash needs grinding first so the new one has clean soil to root into.
Common questions
Frequently asked
Does every ash with dieback need felling?
No. Many infected trees decline slowly and some show tolerance. Felling is usually reserved for trees with heavy crown loss or decay that stand near homes, roads or paths.
How quickly does ash dieback kill a tree?
It varies widely. Young trees can die within a few seasons, while large mature trees may take many years, and some keep most of their crown.
Is a tree with ash dieback dangerous?
It can become dangerous once large branches die, because dead ash wood is brittle. The level of risk depends on how badly the tree is affected and what lies underneath it.
Do I need permission to fell an ash with dieback?
If the tree has a preservation order or is in a conservation area, check with the council first. Exceptions exist for dead or dangerous trees, but it is safest to confirm before work starts.
Can ash dieback spread to other trees in my garden?
The disease affects ash. It spreads by airborne spores from fallen ash leaves, so other ash trees nearby can be infected, but other species are not.
Straightforward advice
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