Ash dieback identification and diagnosis: drought, ash yellows and anthracnose lookalikes

Ash trees in the North West are under pressure. Brown leaves, thinning crowns and dead twigs invite a quick verdict: ash dieback. Sometimes that is right. Sometimes it is not. This guide helps you tell the difference between true ash dieback and its three common lookalikes—drought stress, ash yellows and anthracnose—so you can act with confidence and keep people safe.

Definition. Ash dieback is a fungal disease caused by Hymenoscyphus fraxineus. It infects leaves, travels into shoots, and can form dark, diamond-shaped lesions at twig nodes and on stems. Over time it thins the crown and can predispose trees to failure. In our wet North West summers, symptoms often build from July into September (Forest Research, 2025).

We are seeing a lot of mixed signals at the moment. A dry spell cooks leaf edges. A cool, wet spring shreds new foliage. True dieback adds its own signature at the nodes. The right diagnosis changes your next step: monitor and retain, prune and reduce risk, or remove where targets are high.

A grounded vignette

Last September we inspected a line of ash along a farm access track outside Wigan. From the cab the crowns all looked “burnt.” Up close, two trees carried neat diamond lesions at last year’s side-shoot nodes, and the inner bark under each lesion had turned brownish-grey. The other trees showed uniform leaf-edge scorch with no lesions. The outcome diverged: safety works for the diseased pair; irrigation and soil de-compaction for the drought-stressed remainder (Forest Research; Woodland Trust).

Ash dieback symptoms — what it looks like in the field

Leaf and shoot signs. In mid to late summer, patches on leaflets darken, midribs turn necrotic, and small shoots shrivel from the tip. You may see blackened leaf stalks and premature leaf drop.

Stem and collar lesions. At nodes where a small branch meets the stem, look for lens- or diamond-shaped, dark lesions. If you carefully lift a tiny window of bark beside the lesion, the inner bark is often brownish-grey rather than healthy green. Lesions around the base (the collar) can drive decline.

Timing in the North West. On roadside belts and hedgerows around Greater Manchester and into Lancashire and Cheshire, symptoms usually intensify from July through September. Fallen ash leaf stalks from the previous year can host tiny, pale fruiting cups in summer that release spores into still air along verges and rights of way.

Two checks you can try at home

1. Compare photos from each of the last two summers. Is the upper crown progressively thinning while the lower stem pushes tufts of new shoots?
2. Stand at eye level with last year’s node scars on a sun-exposed twig. Do you see dark, diamond-shaped lesions centred on nodes?

If you see these signs over a play area, pavement or public right of way, book a survey.

Ash dieback lookalike note: drought can mimic tip dieback and early leaf drop, but lacks distinct node-level lesions.

Ash dieback disease stages

How infection builds. The fungus completes its life cycle on fallen ash leaves. In summer, tiny cup-like structures develop on last year’s leaf stalks and release airborne spores. Spores land on new leaves, grow down the leaf stalk into shoots, and can then colonise twigs and stems if leaves do not drop in time. That is why trees under leaf-litter loads beside roads and access tracks can worsen year on year.

Why some trees look worse than others. Site and genetics matter. Young trees decline faster. Ash on heavy clay soils with regular verge compaction or salt exposure often struggle more. Some ash shows partial tolerance; do not remove a safe, healthy ash solely because neighbouring trees are failing. Government guidance encourages retaining safer, healthier individuals to support future tolerance where it is appropriate to do so.

If stages are clearly advancing near a boundary, bus stop or highway, book a risk-led inspection.

Ash dieback lookalike reminder: anthracnose flares in spring and often improves by midsummer.

Ash dieback lookalike: drought stress

Hot spells and compacted, clay-based soils around Greater Manchester and parts of Cheshire can drive water stress. Drought presents as even, margin-to-centre leaf scorch, general yellowing and early leaf drop. Sun-exposed roadside edges are hit first. You will not see diamond-shaped lesions at nodes. After steady rain or watering, leaves can perk up and new shoots may extend.

Two practical tests

• Morning recovery test. Leaves that look droopy at teatime but recover by morning point to water stress rather than infection.
• Soil probe test. Push a long screwdriver beside the root flare. If it stops quickly in hard, dry ground across the rooting area, address soil moisture and compaction before concluding disease.

If foliage scorch sits above a busy right of way and dead twigs are snapping in light winds, book a survey.

Ash dieback lookalike: ash yellows

Ash yellows are caused by a phytoplasma and is well described in North America. Typical signs include smaller, paler leaves, slow twig growth, tufting at tips, witches’ brooms on the lower stem and a slow decline across years. Here is the crucial United Kingdom context: ash yellows are not known to be present in the United Kingdom. It appears on risk registers and is kept under review by plant health authorities. If you suspect witches’ brooms or unusual tufting, do not assume ash yellows; specialist testing is required to confirm or rule it out.

If you think you see witches’ brooms on an ash in the North West, book a professional diagnosis rather than self-treating.

Ash dieback lookalike: anthracnose

Anthracnose on ash loves a cool, wet spring. Young leaves develop water-soaked spots that merge; leaf stalks can be girdled; distorted leaves brown and drop early. Lower limbs can look bare in May and June, then re-foliate by July. There are no diamond-shaped lesions at last year’s nodes. Owners often mistake this for dieback, but the pattern is different and the tree can look much better by high summer once weather dries and warms.

Owner tip: if the tree looks ragged in May but fills out by July, anthracnose is the likely culprit, not progressive ash dieback.

If heavy spring defoliation sits above a car park or pavement, book a survey.

When to bring in a professional assessment (Tree Risk Assessment Qualification)

We structure decisions using the Tree Risk Assessment Qualification approach from the International Society of Arboriculture. In plain English, it means we look at the part that could fail, the chance it will fail, the chance it will hit something or someone, and what the consequences would be. Then we recommend proportionate action.

The steps we follow

1. Identify likely failure parts: dead tops, cracked unions, decayed stems, basal lesions.
2. Judge the likelihood of failure on a scale from improbable to imminent.
3. Judge the likelihood of impact on a target such as a path, road, play area or roof.
4. Combine these to rate likelihood of failure and impact from unlikely to very likely.
5. Weigh consequences from negligible to severe.
6. Recommend actions: retain and monitor, prune, reduce, restrict access, or remove.

If your ash overhangs a school route or a popular path, treat moderate to high risks promptly.

Retain, reduce or remove — choosing a course of action

Pros

• Retain and monitor. Preserves habitat and potential genetic tolerance. Avoids unnecessary loss and cost.
• Reduce and prune. Lowers risk while keeping shade and amenity. Useful where targets are fixed but parts at risk can be made smaller or lighter.
• Remove and replant. Resets risk at high-use sites and enables species diversity suited to clay soils and roadside exposure.

Cons

• Retain. Risk can rise between inspections if conditions change.
• Reduce. Requires repeat works and careful follow-up; not suitable for severely infected stems or advanced collar lesions.
• Remove. Loss of canopy and screening; permissions may apply.

Where it is safe, we support retaining safer, healthier ash to keep options open and maintain structure. Where failure could strike a highway, right of way or play area, act sooner and pair works with clear access management.

If a failing limb overhangs an access track or bus stop, restrict access and book works.

Local realities in the North West

In the North West we often find the worst dieback on exposed coastal stretches toward Merseyside and on compacted clay banks beside Manchester roads. Verge plantings and hedgerows concentrate last year’s infected leaf litter, which can raise spore pressure each summer. Public rights of way place people under canopies more often than you might think. National road teams are actively managing roadside ash in the region; private owners should mirror that risk-led, proportionate approach.

Mini-case from recent work

Location: Altrincham suburban street. Situation: two mature ash trees over a narrow pavement and residents’ parking. Decision: we rated the first tree as likely failure of upper dead tops with a medium likelihood of impact and significant consequence. We reduced the crown and scheduled annual monitoring each July. The second carried extensive collar lesions with poor response; after advising on permissions, we recommended removal and replanting with a mixed species pit for resilience.

If your ash overhangs a right of way or roadside belt, book a risk-led inspection.

TL;DR

• Summer leaf blight together with diamond-shaped lesions at last year’s nodes is the classic ash dieback signature.
• Drought gives even leaf-edge scorch and can improve after rain or watering.
• Anthracnose hits in spring and often re-foliates by July.
• Ash yellows is a North American disease and is not known to be present in the United Kingdom.
• Near paths, roads and play spaces, ask for an inspection based on the Tree Risk Assessment Qualification.

Worried about an ash along a path, play area or roadside in Greater Manchester, Merseyside, Lancashire or Cheshire?

Book an ash health and safety survey. We will diagnose precisely, assess risk using the Tree Risk Assessment Qualification framework, and set out clear next steps. If consents are needed, we will guide you through them.

Get in touch to arrange a visit.

Sources and further reading

• Forest Research. “Ash dieback (Hymenoscyphus fraxineus).” 2025.
• Forestry Commission guidance for England. “Managing ash dieback.” Updated 2025.
• Woodland Trust. “Ash dieback: identification and management.” Accessed 2025.
• Tree Council. “Ash dieback: a guide for tree owners.”
• Department for Environment, Food and Rural Affairs Plant Health Portal. “Rapid Pest Risk Analysis: ‘Candidatus Phytoplasma fraxini’ (ash yellows).” 2016.
• Pacific Northwest Plant Disease Handbook. “Ash anthracnose.” Accessed 2025.
• International Society of Arboriculture. “Tree Risk Assessment Qualification: methodology and matrices.”
• Recent peer-reviewed reviews on ash dieback dynamics and tolerance (2023–2025).

Short disclaimer for the United Kingdom

This guide is for information only. Tree works can require a felling licence and may be restricted by Tree Preservation Orders and conservation area controls. Highways authorities can require traffic management. Always check permissions before undertaking works or removing trees.