Ash dieback (Hymenoscyphus fraxineus) is a fungal disease that has spread through the UK since around 2012. County Durham has been hit hard, and the disease is now common across the county, in towns, villages and the wider countryside. For anyone with an ash tree in the garden, this is the single most important thing to know about it.
What ash dieback looks like
- Dieback of the crown: branches at the top of the tree die back, and the canopy thins out from the outside in
- Dark lesions on the bark, often diamond-shaped, where the fungus has killed the bark
- Epicormic growth: clusters of new shoots sprouting low on the trunk, a sign the tree is stressed
- Withered, blackened leaves that stay on the tree through winter
The disease progresses over years. A tree can look fine one year and lose large limbs the next.
Why it matters
The danger with ash dieback is not usually the whole tree falling over. It is branches shedding without warning. The fungus weakens the wood where it joins the trunk, so heavy limbs can fail in summer, in calm conditions, with no storm to blame. That makes an infected ash near a house, drive, path or power line a real risk.
Ash is also a brittle tree, so when limbs do fail they tend to snap rather than bend.
When an ash tree needs to come down
- More than half the crown is dead. Trees in this state are losing structural strength and the risk of limb failure rises quickly.
- Lesions girdle the trunk or the base of major branches.
- Fungal fruiting bodies (bracket fungi) appear at the base, which can mean the roots or lower trunk are failing.
- The tree is near a target: a building, a road, a car, a place people stand.
A tree with minor crown dieback can often be kept for several years with monitoring and deadwood removal. A tree with heavy dieback near a building should generally come down on a schedule you choose, rather than after a limb drops on something.
What to do
- Look at the crown in summer, when healthy ash is fully in leaf. If a third or more of the crown is thin or dead, take it seriously.
- Check the base for cracks, lifting soil or fungal brackets.
- Get an opinion before it becomes urgent. We inspect ash trees free of charge and tell you honestly whether it can be kept, reduced, or should come down.
- If the tree is in a Conservation Area or has a TPO, permission rules still apply to a diseased tree, although there are exemptions for genuinely dead or dangerous trees. See our permissions guide.
Cost of removing an ash tree
Removal costs the same as any tree of its size: typical felling costs in Durham apply, from around £400 for a medium tree to over £2,000 for a large one near a building, because sectional dismantling is often needed.
If you have an ash tree you are worried about, send us the details. We will come and look, tell you what state it is in, and give you a fixed price and a timeline.