In Focus: Ash dieback disease in the UK

With evidence of ash dieback found in locations throughout the UK, it’s important for land managers to understand how to correctly identify and deal with the disease if found
Ash dieback
There is no known cure for ash dieback

Ash dieback (Hymenoscyphus fraxineus) is now widespread across England & Wales with few areas unaffected. Since first recorded in UK in 2012, spread of this fungal disease has been rapid. Many areas are now suffering significant tree mortality. Also known as Chalara fraxinea, the disease spreads by spores emitted from tiny fruiting bodies on the stalks of decaying leaves.

Ash is the third most common UK broadleaf tree. It is found in open countryside, roadsides and hedgerows and it is also a common hardwood forestry species. Chalara is expected to cause rapid decline and death of most of our ash trees over the next 10-15 years. There is no known cure.

A 2019 study by Sylva Foundation, Woodland Trust and others estimated an economic cost to the UK of £15bn with half of that over the next decade. Landowners therefore need to plan ahead for the inevitable risks and costs of losing most of their ash trees.

A small proportion, perhaps 5%, show natural tolerance. It is important these are retained whilst dealing with diseased ones, so felling controls still apply. Research is underway on the genetic sequencing of ash which will be basis for understanding tolerance and breeding of resistant stock.

Identifying ash dieback – signs and symptoms

The obvious symptoms are foliage loss, crown dieback from peripheral twigs and branches and dark bark lesions. Healthy UK ash should be in full leaf by June, so trees showing these symptoms in summer are likely victims. There are photographic symptoms guides online and reporting sightings via Forest Research Tree Alert helps with monitoring disease spread.

Inspect trees regularly & prioritise action

Under the Occupiers Liability Act 1957, landowners have a duty of care to take reasonable precautions to ensure the safety of trees on their land. For let land, it is important to consult any tenancy agreements and clarify responsibilities for trees.

As well as having adequate insurance in place, trees on your land should be inspected regularly, risks assessed and actions prioritised. A written record should be kept. Trees near public access such as along roads should be prioritised and inspected at least once every two years and proportionate action taken. A useful source is the National Tree Safety Group ‘Common sense risk management of trees’ manual (which has a short ‘landowner summary’).

Staying safe

Chalara affected ash trees are dangerous. Branches become brittle quickly and can shed limbs with little warning. Affected ash also behaves unpredictably when being felled – trunks can split and trees can shatter when they hit the ground. It is essential that staff or contractors are properly qualified, experienced and insured, use suitable equipment and appropriate methods. Climbing and dismantling with chainsaws should be avoided if possible – instead harvesting machines or mobile working platforms are recommended.

The Forestry Industry Safety Accord (FISA) has a useful guidance note on felling dead ash. Employers have duties under the Health & Safety at Work Act 1974 to take reasonable steps to ensure people are not exposed to risks. Failure to observe legal requirements could invalidate insurance and risk prosecution.

Trees that need to be felled require a felling license from Forestry Commission (FC) or Natural Resources Wales (NRW). Approval can take months so it is best to plan ahead and apply early (online is quicker). Some felling doesn’t need a license e.g. when there is immediate risk of serious harm from a dangerous tree and urgent work is needed to remove risk. But the onus is on the applicant to show this exception applies - photographs and/or an experienced consultant’s report will help but FC Operations Note 46a (which has a tree inspection proforma) should be consulted.

If any of the trees you need to fell have Tree Preservation Orders (TPOs) or Conservation Area status then local authority permission is needed beforehand. Operations also need to observe rules on European Protected Species e.g. bats which often roost in trees. It is an offence to damage such habitat but following best practice (see FC Operations Note 46a) will usually avoid the need for a license from Natural England (NE) or NRW.

Road Closures

Dealing with roadside trees may affect traffic and if so, there is an obligation to seek permission from local Highways Authority to work on the highway. Charges vary and approval can take days or months depending on what’s involved eg. a lane closure for a few hours on a country road will be easier and less costly than full road closure of an A road. Need for traffic lights and diversionary signage will raise costs. It pays to co-ordinate activity with neighbours, utilities and local authorities to avoid multiple closures. Even when the road is closed, beware of pedestrians, cyclists and horse-riders.

Funding, compensation & grants

There is currently very limited funding support for owners of trees with ash dieback. Countryside Stewardship Woodland Tree Health provides funding in England for restocking woodlands affected by Chalara. But this does not help with tree felling costs, nor does it offer help for trees outside woodlands. CLA have called on Defra and Welsh Government to include comprehensive tree health support through land management schemes. Further detail is expected from Defra later in 2024.

A tree health pilot has been running in the North West, Midlands and South East of England since 2021, testing different ways of slowing the spread of various tree pests and diseases. Grants are still available through this for groups of two or more applicants collaborating to tackle ash dieback. Grants can help with the costs of road closures, protected species surveys and restocking.

Information & guidance

The good news is that there is now plenty guidance available to landowners on the disease. CLA was one of many organisations which helped to shape the 'Farmer's Guide to Ash Dieback', which covers issues like risk assessment, safety and legal obligations and has embedded videos explaining things in an accessible way.

There is also a dedicated ash dieback webpage on with links to the key information. The Tree Council’s 'Ash Dieback - a guide for tree owners' and the Royal Forestry Society 'Managing ash dieback case studies' are also useful sources.

Overall advice

Ensure you have adequate insurance. Inspect your trees and formulate a plan to address the risks and prioritise action. Consult relevant guidance and get a felling license application in. Line up properly qualified contractors and co-ordinate action with neighbouring landowners and local Highways on any road closures.

Key contact:

Graham Clark
Graham Clark Senior Land Use Policy Adviser, London