Ash dieback in West Sussex
What it is, where it came from, how to spot it and what to do about it, from a qualified local team based in Horsham.
A big change for West Sussex
Ash dieback is one of the biggest changes to the West Sussex landscape in a generation. Ash is one of the county's most common trees, and West Sussex County Council has warned that most of them could be lost.
If you own or look after land with ash trees, it helps to know what the disease is, how to spot it and what to do next. This guide covers all of that, and what is happening in West Sussex right now.
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What is ash dieback?
Ash dieback is a disease of ash trees caused by a fungus called Hymenoscyphus fraxineus. It affects common ash, the UK's native ash tree, and other ash species, and it can infect trees of any age. Young trees and saplings tend to decline the fastest.
The fungus attacks the leaves first, then grows into the twigs, branches and sometimes the trunk, damaging the tree's ability to move water and nutrients around. Over several seasons the crown thins and dies back.
It spreads on the wind. In summer the fungus produces tiny fruiting bodies, about the size of a match head, on the stalks of fallen ash leaves from the year before. These release huge numbers of spores that can be carried a long way. It can also travel with the movement of infected plants and logs.
Where did ash dieback come from?
The fungus comes from East Asia, where it lives on local ash species without doing them much harm. European ash never had the chance to evolve any defence against it.
- East AsiaA leaf fungus that is widespread and relatively harmless to Asian ash species.
- 1992, PolandFirst seen in Europe, probably arriving on ash plants imported from Asia.
- 1990s to 2010s, EuropeSpread west across the continent, causing heavy losses in places such as Norway and southern Sweden.
- February 2012, BuckinghamshireFirst found in the UK, at a nursery, on young ash plants imported from the Netherlands.
- 2012, East AngliaFound in the wider countryside, where spores may also have blown across from the continent. The government banned the import and movement of ash plants in October 2012.
- TodayFound across the UK, including West Sussex.
Genetic research suggests that Europe's whole outbreak may have started from just one or two fungal fruiting bodies.
What to look for
Ash dieback is easiest to spot in summer, when the trees are in leaf, so that is the best time to check. Ash trees have leaves made up of several pairs of leaflets, branches and buds that grow in opposite pairs, and distinctive black buds in winter.
Leaves
Dark brown patches or spots in summer, and leaves that wilt and die early.
Shoots and twigs
Shoot tips that turn black and die back, with leaves wilting on them.
Bark
Dark, diamond-shaped lesions on branches and the trunk, which can look like bruises.
The crown
A thin, sparse crown with dead branches, as dieback works its way down from the top.
Epicormic shoots
Clusters of new shoots sprouting straight from the trunk or main branches as the tree struggles to cope.
These signs can also have other causes, such as drought, other diseases or honey fungus. A proper inspection by someone qualified is the only way to be sure, and to judge how safe the tree is.
What is the solution?
There is no cure for ash dieback, and no spray or treatment that stops it. So the focus is on managing it well: keeping people and property safe, while holding on to as many trees as we safely can. Every tree is different, but this is how we think about it.
Keep and monitor
Trees with a healthy crown and little dieback. Check them each summer. A small number of ash show real tolerance to the disease and matter for the future of the species, so a healthy-looking ash should not be felled just because it is an ash.
Reduce or watch closely
Trees with noticeable dieback. Away from roads, paths and buildings, they can often be left and monitored, which also keeps habitat. Near people, we may reduce the crown or remove dead limbs to lower the risk.
Make safe
Trees with serious dieback, and dead or dying trees, especially near roads, buildings, paths and play areas. Diseased ash can become brittle and fail with little warning, so these are usually taken down safely as a priority.
This is only a guide. Each tree needs to be looked at on its own merits.
Other things that help
- Reduce local spread: if you only have a few trees, rake up fallen ash leaves in autumn and burn (where permitted), bury or deep compost them.
- Replace what is lost: plant a mix of species rather than relying on one. See our tree and hedge planting.
- Check the rules first: trees with a Tree Preservation Order or in a conservation area normally still need consent from the local council, a felling licence may be needed for larger amounts of timber, and nesting birds and bats must be protected.
- Know who is responsible: as the landowner, you are responsible for ash trees that could fall onto roads, paths, neighbours or buildings.
The current situation
Across the UK
Ash dieback has now been found throughout the UK. Estimates vary, but the Woodland Trust says it could kill up to 80% of the UK's ash trees, and some local councils are planning for even higher losses. The cost to Britain has been predicted at £15 billion. Experts now expect us to be living with the disease for decades rather than years.
In West Sussex
West Sussex is hit harder than many places because ash is so common here: around 21% of the county's broadleaved trees are ash. West Sussex County Council expects that up to 95% of the county's ash trees could be lost. It has been surveying and felling infected ash beside the roads for several years, including the A24 Horsham bypass and Southwater bypass and stretches of the A272 and A29, under its duty to keep the highway safe.
Where ash trees on private land are within falling distance of a road, the council writes to the landowners, advising them to arrange their own survey.
Where the science is
There is some hope. Around 1% of ash trees show a high level of tolerance to the disease. The Living Ash Project, led by Forest Research and partners, has gathered material from many of these trees into a national archive so it can be used to breed more tolerant ash, and some monitored trees have even healed their lesions. It will take years before tolerant ash can be planted at scale, but it suggests ash can survive in our landscape.
Information last checked October 2026. The situation changes, so check the latest guidance below.
How we can help
- Ash tree inspections: we look at your ash trees and advise tree by tree.
- Safe felling: including sectional dismantling near roads, buildings and gardens.
- Reduction and deadwood removal: where a tree can be kept safely for now.
- Woodland work: thinning, clearing and chipping across larger sites. See our woodland management.
- Replanting: choosing and planting suitable replacements. See our tree and hedge planting.
- Advice on permissions: TPOs, conservation areas and felling licences.
- Emergency call-outs: for ash trees that have failed or dropped limbs. See emergency call-outs.
Ash dieback questions
Does my ash tree have ash dieback?
Look for dark patches on the leaves in summer, dead twigs and branches in the crown, dark diamond-shaped lesions on the bark, and clusters of new shoots on the trunk. Summer is the best time to check, because the tree is in leaf. These signs can have other causes, such as drought or other diseases, so if you are unsure we can inspect the tree and tell you what is going on.
Do I have to cut down my ash trees?
Not always. Finding ash dieback on a tree does not automatically mean it must come down, and some ash show real tolerance to the disease. But if a tree is near a road, path, building or garden and could cause harm if it failed, it needs to be made safe, and that usually means felling or reducing it.
Can ash dieback be treated or cured?
No. There is no known cure and no treatment that stops the disease. Management is about keeping people safe, keeping healthy-looking and tolerant trees where it is safe to do so, and replanting.
Is an ash tree with dieback dangerous?
It can be. Diseased ash can become brittle, so branches can drop and whole trees can fail with little warning, especially in wind. Trees with serious dieback near people or property should be assessed promptly.
Do I need permission to fell an ash tree with dieback?
It depends. Trees with a Tree Preservation Order or in a conservation area normally still need consent from the local council first. A felling licence may be needed for larger amounts of timber, and we have to protect nesting birds and bats. We will check what applies before any work starts.
Who is responsible for ash trees beside the road?
West Sussex County Council looks after ash trees that it is responsible for beside the highway. Ash trees on private land are the landowner's responsibility, and the council writes to landowners where infected trees are within falling distance of a road, advising them to arrange their own survey.
What should I plant to replace ash?
A mix of species is best rather than relying on one. Oak, field maple, hornbeam, lime, hazel and birch are all good options, and the right choice depends on your soil and site. We can advise and plant them for you.
Which areas do you cover?
We are based in Mannings Heath near Horsham and cover ash dieback surveys and tree work across West Sussex, including Horsham, Billingshurst, Southwater, Cowfold, Henfield, Storrington, Nuthurst and Lower Beeding.
Ash dieback help in Horsham and West Sussex
- Horsham
- Broadbridge Heath
- Christ's Hospital
- Southwater
- Mannings Heath
- Lower Beeding
- Nuthurst
- Maplehurst
- Cowfold
- Bolney
- Henfield
- Partridge Green
- Barns Green
- Billingshurst
- Storrington
Worried about an ash tree?
Call Max or send a few photos on WhatsApp and he can tell you what to look at next.