Why Ash Matters — and Why Careful Checking Pays Off

Ash is one of the most familiar broadleaves in the British countryside. It suits our heavier, base-rich soils, regenerates freely, and has long been prized for tool handles, hurdle gates and firewood. Millions grow in hedgerows, parkland, streets and farm woodland, quite apart from the many millions in our larger woods, where ash often forms the main canopy on limestone and clay. That ubiquity is exactly what makes ash dieback so significant. The disease, caused by the fungus Hymenoscyphus fraxineus, was first confirmed in Britain in 2012 and is now established across most of England, Wales, Scotland and Northern Ireland.

Most infected trees eventually decline, but a small proportion show real tolerance and live on. Finding those survivors matters, and so does spotting symptoms early — both for safety planning and for recording how the disease is behaving on your site. Walk your woods between June and September, and again in late winter when the bare crowns make dieback easiest to read.

Leaf and Shoot Symptoms: The First Clues

Infection usually shows first in the foliage. Rather than a general yellowing, you are looking for leaves that wilt, darken to a blackish-brown and fall while still green — long before autumn. The discolouration often begins near the midrib or at the leaflet tips and spreads unevenly, leaving a mottled, scorched appearance across the crown.

• Wilting, blackened leaves in mid to late summer, dropping prematurely and often carpeting the woodland floor under affected trees.
• Blackened, shrivelled shoots where the fungus has killed the current year's growth; these frequently curl into a distinctive shepherd's crook shape.
• Dormant buds that never break, leaving bare sections of branch beyond the infection point.
• Epicormic growth — tufts of vigorous shoots appearing on the trunk and lower branches as the crown thins.
• Crown dieback progressing from the top down, thin and spindly at the very top of the canopy first.

The key point is that these signs cluster together. A single blackened shoot in a vigorous tree is not proof; repeated shoot death, thinning foliage and a crown dying back from the tips very much is.

Bark and Stem Symptoms: Diamond-Shaped Lesions

As the fungus moves through the branch structure, it reaches the wood and kills the cambium. This produces the lesion that most people learn to recognise: an elongated, diamond-shaped patch on the bark, often sitting where a side branch or dormant bud meets the stem. Fresh lesions look olive-brown to grey-brown with a dark purple-brown rim; older ones become sunken, silvery and cracked, with a pronounced raised margin.

If you carefully lift a small strip of bark at the edge of a lesion, the wood beneath will be stained greyish-brown rather than the pale cream of healthy ash. On young trees, lesions at the base and root collar are particularly damaging, girdling the stem quickly and causing sudden collapse. On mature trees, look for the telltale diamonds high in the crown and on major limbs, difficult to see from the ground but obvious from a distance once the canopy thins.

Other Things It Could Be

Ash has plenty of other troubles, and a mistaken diagnosis helps nobody. Before you make a judgement, rule out the alternatives.

• Ash bud moth — blackened terminal buds in spring, with tiny pellets of frass nearby, but no bark lesions.
• Grey squirrel damage — bark stripped from upper branches and main stems, with obvious tooth marks and no diamond-shaped pattern.
• Drought or waterlogging — uniform leaf scorch and premature fall across many species, not just ash.
• Verticillium wilt — dieback often one-sided, with dark green staining in the outer wood rather than grey-brown.
• Phytophthora and old cankers — bleeding or resinous patches at the collar, sometimes resembling ash dieback lesions on young trees.

A useful rule of thumb: dieback lesions follow the line of a shoot or branch, sit around a bud or branch junction, and usually come with blackened shoots in the canopy above them.

Reporting a Suspected Case

Good records make a real difference. Before reporting, note the grid reference, the number and rough age of affected trees, and the proportion of the crown showing symptoms. Take photographs of the whole tree, a close-up of the lesion with something for scale, and the undersides of affected leaves.

Report suspected cases to the appropriate woodland officer or the statutory plant health authority for your part of the UK — the Forestry Commission in England, Natural Resources Wales, Scottish Forestry or DAERA in Northern Ireland. The TreeAlert reporting service is the quickest route for most woodland owners and is straightforward to use from a phone in the field. Then take sensible precautions: do not move ash timber, brash or nursery stock from an affected site to a clean one, and clean boots and tools before leaving.

Managing a Woodland Once Dieback Is Confirmed

Safety comes first. Trees beside roads, footpaths, bridleways, boundaries and power lines should be assessed as a priority, and dying ash becomes brittle surprisingly quickly. Where felling is needed, plan it in phases over two to three years rather than clearing everything at once.

Resist the urge to fell all your ash. Leave healthy-looking trees with less than about 20 per cent crown dieback standing — they may carry tolerance worth inheriting — and monitor them each year. Away from targets, standing dead ash is superb habitat for beetles, fungi, woodpeckers and bats, so retain some where it is safe to do so. Restock with a diverse mix suited to the site: oak, birch, hornbeam, small-leaved lime, field maple, wild cherry and a good shrub layer. Natural regeneration of other species is free and often the best option. With patience and selective thinning, a woodland can come through this — and the tolerant ash that survive will be the ones worth propagating for the future.