Ash dieback: signs, risks and what to do

Ash dieback is a fungal disease, Hymenoscyphus fraxineus, that kills the shoots, branches and eventually the whole crown of common ash. If your ash has a thinning crown, blackened leaves in late summer, dead twigs at the ends of the branches and tufts of new growth sprouting from the trunk, it is very likely infected. What you do next depends on where the tree stands. An ash in the middle of a field can be left to decline. An ash over a road, a footpath, a driveway or a house needs looking at by someone qualified, because diseased ash becomes brittle and unpredictable long before it looks dead, and the landowner carries the legal responsibility for what it does. Not every infected ash has to be felled.

This guide is general information, not legal advice.

What it looks like, season by season

Ash dieback is easiest to confirm in mid to late summer, which is when Forest Research recommends surveying. Leaves develop dark patches, then wilt and discolour to black, and often drop early, along with the shoots they are on (Forest Research). Late summer into autumn is also when the fungus fruits, on the stalks of last year's fallen ash leaves under the tree. Spores travel on the wind over tens of miles, so there is nothing a garden owner can do to keep the disease out.

All year round, look at the bark. Infection running back from a dead shoot forms dark lesions, or cankers, centred on a branch joint and often shaped like an elongated diamond. Where a lesion girdles a whole stem it cuts off the flow of water and nutrients above that point, which is why one lesion low on the trunk matters far more than one out in the crown.

In winter, with the leaves off, the shape tells the story: bare, blackened twig ends, whole sections of the outer crown dead, and dense shoot clusters on the trunk and main branches. That is epicormic growth, the tree's response to losing its crown, and a heavily epicormic ash with a thin outer crown is the classic picture of the disease.

Basal lesions at the foot of the trunk worry arborists most. Government guidance notes that lesions at the base leave the tree more open to secondary infections such as honey fungus, and it is that combination, disease in the crown and rot in the butt, that produces sudden whole-tree failure.

How fast it moves

There is no fixed timetable. Government guidance says severity varies locally, that trees in woodland with a high proportion of ash decline faster because of the higher spore load, and that trees standing alone in hedgerows and gardens may deteriorate more slowly or persist indefinitely (Managing ash dieback in England). Young and coppiced ash can be killed quickly; large old trees usually take several years and decline in steps. The disease was first identified in England in 2012, and ash makes up about 12% of Great Britain's broadleaved woodland.

Why it is dangerous to work on

This is the part most people do not expect. Diseased ash does not get weaker in proportion to how dead it looks. The wood turns brittle, and branch and stem fibres fail suddenly rather than bending first. Industry guidance is that infected trees can become unpredictably brittle and unsafe to climb before they are even half dead, and that close inspection and works should be planned using a mobile elevating work platform rather than by climbing.

So a competent tree surgeon may look at your ash and decline to climb it. That is the right answer, not an excuse to charge more. The alternatives are a MEWP or cherry picker, a crane or grab lorry, mechanical felling, or straight felling from the ground where there is room to drop it. All of those need access, and access is what drives the price. Rope-and-harness work on visibly diseased ash is a last resort needing strong justification and full rescue planning, because an anchor point can fail without warning. A cheap quote to climb a clearly diseased ash is a warning rather than a bargain. See do tree surgeons need to be qualified.

Your duty as the owner

The owner of land where a tree stands is legally responsible for the health and safety of those who could be affected by that tree. Government guidance is explicit that if you manage ash near roads, railways, buildings and other publicly accessible land you must consider the risks and should carry out a risk assessment.

For a homeowner that does not mean a survey every year. It means looking at the tree, acting when it changes, and keeping a note of when you last checked and what you did. Where a tree could hit a road, a footpath, a neighbour's house or a place people sit, a written assessment from an arboricultural consultant is worth having, because it is evidence that you took reasonable care.

Permission still applies

A diseased ash is not automatically exempt from tree protection.

• With a Tree Preservation Order, you normally still need consent. Dead trees need five working days' written notice instead, and a tree presenting an immediate risk of serious harm can be dealt with provided you notify the council as soon as practicable afterwards. Government guidance is clear that if the danger is not immediate the tree does not come within that exception, and a living ash with dieback is usually neither dead nor an immediate danger. See how to check if a tree has a TPO.
• In a conservation area without a TPO, you give the council six weeks' notice under section 211. See trees in conservation areas.
• Felling licences apply to woodland rather than garden trees. Government guidance says felling diseased ash requires a licence unless the trees are dead or pose a real and immediate danger, so a farm or woodland owner needs to check first.

The point in do I need permission to cut down a tree holds: find out before the saw starts.

Not every ash has to come down

Government guidance says it is likely that the majority of native ash will show symptoms, but not all will die, and that some ash have genetic tolerance, meaning they may survive and reproduce. The Woodland Trust cites up to 80% of UK ash lost with 1% to 5% showing reasonable tolerance, and puts the predicted cost to British society at £15 billion.

The advice that follows is to retain ash that stand out as healthier than those around them where it is safe to do so, and to keep dead and dying wood that threatens nothing, because standing deadwood is good habitat. A reduction or a deadwood clean can buy a well-placed tree several more years. Removal is the answer for trees over targets, not for every ash on the plot.

Disposal and biosecurity

There is no requirement to burn or destroy infected ash, and the disease is already widespread, so wood can be chipped, logged and left on site. The Woodland Trust suggests collecting fallen ash leaves and burning, burying or deep composting them to interrupt the fungus, which fruits on last year's leaf litter. Ordinary biosecurity still applies: the Forestry Commission's Keep it Clean advice is to arrive clean and leave clean, with boots, tools, ropes and saws free of soil and organic material. Before burning anything, read can I burn garden waste, and green waste removal covers pre-cut piles.

What it costs

Indicative ranges from our price card, waste included. Ash dieback work often lands at the top of a range or goes to survey, because of the MEWP or crane time.

Anything over £1,200, over 15m, over a road, near cables or touching a building goes to a free survey first. There is a £150 job minimum.

Getting it looked at

We are an introducer: we pass your enquiry to one vetted local tree surgeon who covers your area, and they confirm a fixed price. Start with tree removal or tree felling and the tree removal cost guide. If the tree is worth keeping, see crown reduction and the crown reduction cost guide, and stump grinding for what is left. Read what to photograph for a tree quote first, and include a clear shot of the base of the trunk.