Ash dieback on your boundary: identifying and managing an infected hedgerow ash.

Trees & disease risk · Updated 26 September 2026

Ash is now one of the most common tree-risk worries across the Tenterden Weald. Not because ash is structurally weaker than other species in its prime, but because ash dieback progresses quickly once it takes hold, and the pattern of die-off, dead limbs high in the crown, green epicormic regrowth pushing out from the base, can make a structurally compromised tree look more reassuring than it sometimes is. Getting the assessment right before deciding whether to fell, reduce or monitor a diseased hedgerow ash is the whole job.

A diagnostic checklist: what you are seeing

The signs of Hymenoscyphus fraxineus appear in a recognisable sequence. Work through these four indicators against what you can actually observe from the ground:

1. Blackened or wilting leaves in summer. Healthy ash is one of the last trees to produce leaves in spring and one of the first to drop them in autumn. If leaves that opened normally in April or May then blacken, wilt and hang in place through June and July, that is ash dieback until proved otherwise. This is distinct from drought stress, which produces marginal leaf scorch but rarely a complete collapse of foliage in full leaf while the rest of the landscape is green.
2. Diamond-shaped bark lesions at dead shoot bases. Look at the bark exactly where a dead shoot or a dead branch section meets live wood. Ash dieback leaves a characteristic elongated, diamond-shaped or lens-shaped dead patch, often with an orange-brown stain under the surface bark. This is the single most diagnostic sign: it confirms the identification and distinguishes ash dieback from other causes of crown dieback such as weather damage or root disturbance.
3. Epicormic growth from the trunk or root collar. A healthy ash in reasonable conditions does not throw masses of thin vigorous shoots from the main stem or from the base of the trunk. A tree fighting advanced ash dieback does, because it is attempting to maintain photosynthetic capacity as the upper crown fails. A cluster of leafy growth erupting directly from the trunk or from the root collar is the tree's own distress signal, and on an established Wealden hedgerow ash it is almost always ash dieback.
4. Crown dieback advancing from the top down. The disease typically kills the uppermost and outermost branches first and works inward and downward. A tree with a bare upper canopy and still-green lower branches is at an intermediate stage. A tree where the dieback has consumed the main scaffold limbs, or where less than a third of the canopy is still in leaf, is at an advanced stage requiring a decision.

Assessing the structural risk

Not every infected ash is an immediate felling job, and Forest Research guidance on managing ash trees (Operations Note 46a and the Chalara manual), alongside the Woodland Trust's identification guidance, describe a proportionate approach based on the degree of infection and the proximity of the tree to people and infrastructure. As a working guide:

• Under 25% crown dieback, no epicormic growth present: early-stage infection, monitor annually. No urgent action is required unless the tree directly overhangs a road, driveway in regular use, or occupied building.
• 25-50% crown dieback with epicormic growth: advancing infection. In a rural boundary or field corner away from daily foot and vehicle traffic, continuing to monitor may be appropriate. If the tree overhangs a highway, a domestic garden where children play, or any structure in regular use, an arboricultural inspection is sensible at this point.
• Over 50% crown dieback, especially with trunk lesions visible: the structural risk is real. A tree in this condition needs either a formal arboricultural assessment to determine whether a crown reduction can safely extend its serviceable life, or a felling programme. Before any decision is made, the root collar should be probed or cored for internal decay, because exterior appearance can significantly understate the extent of internal structural damage at this stage.

The specific risk factor on Wealden clay deserves a note. Clay retains water, and on a saturated clay site in a wet winter, the mechanical grip of a root plate is genuinely weaker than on free-draining chalk or sand ground. A root collar compromised by decay on waterlogged clay is a more immediate safety concern than the same condition on a well-drained site. It is a good reason to have a root collar checked by a qualified arborist before deciding what to do. I prune and reduce hedges; I do not fell trees or grind stumps.

Conservation area and TPO: the paperwork doesn't stop for a dying tree

This is where I encounter the most confusion, and where the consequences of getting it wrong are most serious. A tree being diseased or dying does not suspend the legal paperwork requirements.

Inside the Tenterden conservation area (Ashford Borough Council ref CA-43, designated 10 October 1996), any works to a tree stem exceeding 75mm in diameter measured at 1.5m above ground require six weeks' written notice to Ashford Borough Council before the work starts, under section 211 of the Town and Country Planning Act 1990. That notice requirement applies to a dying ash just as much as to a healthy one. The exceptions are a tree that is actually dead (five working days' written notice before the work, with evidence) and one that is an immediate risk of serious harm (do only the work needed, then notify as soon as practicable). The council's window to make a Tree Preservation Order runs from the date of your notice: if they don't act within six weeks, you may proceed. I file section 211 notices on behalf of clients as part of the job, at no additional charge, but I need the address before quoting to confirm whether it falls inside the CA boundary.

Separately, check whether the specific tree carries a Tree Preservation Order. A TPO does not lapse when a tree becomes diseased. You still need consent from Ashford Borough Council before working on a protected tree that is dying but not yet dead; the exceptions are limited to dead trees (five working days' written notice first) and immediate risk of serious harm (notice as soon as practicable afterwards). Carrying out unpermitted works on a TPO tree can lead to a fine of up to £20,000 in the magistrates' court, and an unlimited fine in the Crown Court. The Rolvenden and Biddenden village conservation areas carry the same 75mm-stem, six-week-notice requirement as the Tenterden CA; if your tree is anywhere near a village CA boundary, I check the address against the Ashford Borough Council map before any work starts.

Replacement planting after an ash is lost

An ash felled or reduced to a stump leaves a gap in the boundary that is worth filling. On Wealden clay, the native species that work as hedgerow standards and tolerate the drainage conditions are: field maple (Acer campestre), crab apple (Malus sylvestris), wild cherry (Prunus avium) and hornbeam (Carpinus betulus). All four are native to the High Weald, cope with clay if the planting pit is properly prepared to at least 600mm depth, and are not affected by ash dieback, though no tree species is free of pests and diseases. See the Weald species guide for the full breakdown by soil type and position across the Tenterden area.

Sources: Forestry Commission Operations Note ON046a, Managing individual and small groups of ash trees (Forest Research, updated 2020); Woodland Trust, How to spot the signs and symptoms of ash dieback (November 2023); Wildlife and Countryside Act 1981 s.1; Conservation of Habitats and Species Regulations 2017; Town and Country Planning Act 1990 s.211; GOV.UK, Tree Preservation Orders and trees in conservation areas; Ashford Borough Council conservation areas register (CA-43, Tenterden, designated 10 October 1996).