Getting to know your woodland's baseline

The best disease spotters are rarely pathologists. They are the people who walk the same wood every week and notice when something shifts. Before you can recognise a problem, you need a feel for what healthy looks like: the species mix, the age of the stands, which trees leaf first in spring and which hold their leaves longest in autumn. Photograph the same viewpoints each season. That record becomes an early warning system, because a tree that thins its crown in July stands out sharply against a woodland you know well.

Carry a hand lens and a notebook. Look up as often as you look down, since most problems show in the canopy long before the trunk reveals anything obvious.

Ash dieback: the chalara tell-tales

Ash dieback has reshaped hedgerows and woods across the country, and it is the disease you are most likely to meet. It spreads on the wind and in the movement of young trees, and usually enters through the leaves.

• Shoot dieback: young shoots blacken and wilt in summer, often bending into a shepherd's crook shape.
• Leaf symptoms: dark blotches and a blackened midrib, followed by early leaf fall.
• Crown thinning: the canopy loses density from the top and outer edges first, letting in more light than usual.
• Bark lesions: diamond or lens-shaped dark patches on branches and trunk.
• Epicormic growth: a burst of bushy shoots from the trunk and lower branches.
• Fruiting bodies: small white discs on blackened leaf stalks on the ground in late summer.

Healthy-looking ash can carry the fungus for years, so check the same trees annually rather than writing them off at the first brown leaf.

Honey fungus: the underground threat

Honey fungus kills roots and spreads through soil, which makes it far harder to spot than a leaf problem. It often attacks trees already stressed by drought, compaction or waterlogging, travelling along buried roots and old stumps.

• Bootlaces: black, root-like strands in the soil or under bark at the base.
• White fans: creamy sheets of fungal tissue between bark and wood, smelling faintly of mushrooms.
• Sudden decline: a tree that looked fine in spring goes pale, then brown, then dead within a season.
• Rings of death: affected trees often die in an expanding circle as the fungus moves outward.
• Autumn mushrooms: honey-coloured toadstools clustered on stumps in September and October.

Take care when digging out stumps, and never move soil from an infected area into a clean one.

Other diseases worth knowing

Beyond ash and honey fungus, a handful of other problems are common enough to keep on your radar.

• Phytophthora ramorum: dark bleeding lesions on larch trunks, browning needles and rapid crown death. Beech and sweet chestnut can also be affected.
• Oak processionary moth: white silken webbing nests on oak trunks in summer. The hairs are a health hazard, so keep your distance and report sightings.
• Horse chestnut bleeding canker: sticky dark ooze on the trunk, often with cracked bark above it, leading to crown dieback.
• Dutch elm disease: leaves wilt and yellow on one branch in midsummer, then the whole crown, with brown streaking under the bark.
• Acute oak decline: dark, weeping patches on oak trunks, sometimes with small beetle exit holes nearby.

What to do when you spot something

Note the date, the grid reference and the species, and photograph the whole tree, the crown and the specific symptom. Report anything unfamiliar to your national plant health authority, and do not move timber, logs or plant material out of the area — many of these problems travel further in the back of a truck than they ever do on the wind.

Clean tools and boots between visits, especially pruning saws and chains. If a dying tree stands near a footpath, fence or fell it before it becomes a hazard. When you replant, aim for a mix of species suited to the site rather than a single replacement, so the next generation of woodland is less vulnerable.

Care, craft and the timber that remains

Diseased woodland still yields honest material, and there is quiet satisfaction in using it well. Ash that is sound above the lesions makes excellent tool handles, chair legs, gates and hay rakes; green woodworkers prize it for its straight grain and shock resistance. Felled material is best processed where it grew. Season firewood properly, and consider charcoal burning or biochar for the smaller, knotty pieces that are no use on the bench.

Leave a proportion of deadwood standing or on the ground. Beetles, fungi, bats and woodpeckers depend on it, and a wood with some decay in it is a functioning wood, not a failing one. Spotting disease early is not about saving every tree; it is about knowing your woodland well enough to make good decisions, keep people safe, and carry on the craft that has always grown out of careful care.