Apple Canker: How to Identify and Treat It

What is apple canker and what causes it?

Apple canker is caused by the fungus Neonectria ditissima. It lives in the bark and wood of apple, pear and a handful of other trees, and it almost always gets started at a wound of some kind rather than attacking healthy, undamaged bark on its own.

The fungus kills bark tissue locally, which is why the infected area looks sunken and discoloured compared with the healthy bark around it. On older lesions you'll often see concentric rings, a bit like growth rings, because the fungus advances in bursts whenever conditions turn favourable and then pauses again.

In autumn and winter, small reddish fruiting bodies form along the edge of the wound. These release the spores that infect new wounds nearby. In spring, you'll often see creamy-white, slightly spongy spore masses in the same spots instead.

One detail that's easy to miss: an old canker doesn't stop being infectious just because it's been sitting there for a few years. A neglected lesion keeps producing fresh spores season after season, effectively acting as a standing source of infection for the rest of the tree and any neighbours nearby. That's a big part of why old, ignored cankers tend to be the root cause behind a cluster of "new" infections showing up elsewhere in the canopy.

Good to know. You'll see this fungus under a few different names in older references — Neonectria ditissima, Neonectria galligena and the older Nectria galligena. They all refer to the same organism and the same disease.

Is it the same disease on pears?

Yes. The same fungus causes canker on pear trees, and treatment is identical. Pears tend to be affected a little less often than apples in most home gardens, but when canker does show up on a pear it looks and behaves the same way. If you're growing both, it's worth checking each one — spores move freely between the two.

How to identify apple canker

What canker looks like depends a lot on where it is and how long it's had to develop.

On thin branches and twigs

Here things move fast. An infection can girdle a thin branch — spread all the way around its circumference — and kill everything beyond that point within a single season. The branch wilts, the leaves brown off, and they'll often hang on for a while before dropping.

On larger branches and the trunk

On thicker wood, canker tends to become chronic instead. You'll see an elongated, sunken lesion with visible rings expanding outward from an old wound — often a previous pruning cut or an old frost crack. The bark at the centre may split and eventually fall away, exposing dead wood underneath.

On the fruit

Fruit can be infected too, showing up as sunken, soft rot, often with the same reddish fruiting bodies you'd see on branches. Infected fruit tends to drop early.

A quick way to tell canker from ordinary bark damage: a scrape or scuff heals over time and forms a fairly even callus ridge. Canker does the opposite — the lesion keeps growing, year after year, if it's left alone.

Which trees are most at risk?

Apples are by far the most common host in home gardens, with pears a close second. Some deciduous trees can also carry it, including rowan, ash, beech and poplar, though it's less common on these and rarely causes the same level of damage as on fruit trees.

Young trees are especially vulnerable. Their bark is thinner, they have fewer reserves to heal with, and they typically collect more small wounds in their first few years — from staking, planting shock and frost — than an established tree.

Nursery stock isn't entirely clean either. Surveys of nursery trees have found that a small share, roughly around one percent on average but considerably higher in some batches, already carry a latent infection at the time of sale. That's a good reason to inspect a new tree carefully before you plant it, and not to panic if you spot a single small lesion in its first year.

In practice, that means giving a new tree a proper once-over before it goes in the ground. Pay particular attention around the graft union and any marks from staking or transport at the nursery. A small, already-healed scar is rarely a problem; a fresh, sunken patch is worth asking the nursery about before you plant.

How the disease spreads through the year

Apple canker really spreads in two distinct waves over the course of a year.

In spring, the reddish fruiting bodies release spores that can travel a fair distance — in some cases well over a hundred metres — carried by wind, rain splash, insects, and even on hands and tools. This is usually the spread responsible for new infections on neighbouring trees, or on a different part of the same tree.

Over summer, a second type of spore forms and spreads over much shorter distances, mostly through rain splashing it from an existing lesion onto a nearby wound. That spread is more local, but it's still enough to infect a freshly pruned cut in the same canopy.

Research has found that spores can spread as soon as temperatures climb above roughly 5°C (41°F), which in most temperate climates means the risk window covers a large part of the year rather than just the height of summer. Wet weather sharply raises the risk, while a dry spell makes it much harder for spores to germinate on exposed wood.

Rain splash matters more than most gardeners assume. A heavy downpour can throw spores several metres up and sideways from an active lesion, which is one reason several "new" lesions sometimes appear in the same part of the canopy right after a particularly wet stretch. A tree growing close to another infected tree, or with branches that cross and rub, carries somewhat higher risk than one with plenty of airflow between the branches.

Almost every infection needs a wound to get started. The most common entry points are:

• Pruning cuts, especially large ones
• Frost cracks and cold damage
• Hail damage to bark and young shoots
• Wounds from woolly aphid feeding and other insect damage
• Natural leaf scars where a leaf was attached to the shoot

That's also why canker so often turns up right at old pruning cuts or in branch crotches, where both moisture and old wounds tend to accumulate.

Rough pruning windows by USDA hardiness zone, aimed at avoiding the wettest, coldest stretches of the year

Treat this table as a rough guide rather than a strict rule — the specific weather in a given year matters at least as much as the zone. The underlying principle holds everywhere: prune while the tree is actively growing and can heal quickly, and avoid making cuts right before a stretch of cold, wet weather.

What to do now: treating an infected tree

If you've already found a lesion, it's usually better to act now than to wait for the "ideal" pruning season, especially if it's actively girdling an important branch. Pick a dry spell if you have the choice, but don't let an active lesion sit for months just because the calendar isn't perfect.

1. Assess how far it's spread. A lesion on a thin side branch can usually be removed entirely. On a main branch or the trunk, you'll need to judge how much of the circumference is already affected.
2. Remove the whole branch for minor infections. For thin branches and twigs, cut the entire branch off a little way into clean wood — not just the visibly damaged part. Cut back to a fork or flush with the parent branch rather than leaving a stub.
3. Cut the lesion out on larger branches. If removing the whole branch isn't practical, cut out the canker itself with a sharp, clean knife until you reach nothing but healthy, pale wood and clean bark all the way around the edge.
4. Disinfect your tools between cuts. Wipe your secateurs or knife with rubbing alcohol between each infected branch, so you don't carry spores from one wound straight onto your next clean cut.
5. Protect larger wounds. On a big, carved-out wound, a thin layer of wound sealant or pruning paint can help stop the cut surface from drying out and cracking while it heals. Ordinary, smaller pruning cuts usually don't need it.
6. Get the prunings out of the garden. Burn them or bin them with your regular green waste collection rather than composting them — infected wood can keep producing spores from inside a compost heap.
7. Keep an eye on the cut. If the lesion comes back in the same spot the following season, you probably didn't cut far enough into healthy wood the first time. Go back and cut a little further in.

Common mistake. Just tidying up the edge of a lesion instead of cutting all the way into clean, pale wood. Leave even a small rim of infected tissue behind and the fungus carries on growing there — the lesion is usually back within a year.

If canker has worked its way all the way around the trunk — fully girdling the tree — there's unfortunately no way to save it. Water and nutrients can no longer move past the dead ring, and the tree will decline regardless of what you do above the wound. At that point, the tree needs to come out; you can either plant elsewhere or wait a season or two before putting a new fruit tree in exactly the same spot.

Does fertilizer make canker worse?

This connection rarely gets mentioned, but it's worth knowing if you fertilize your fruit trees regularly.

Research specifically on apple canker has found a clear pattern between nitrogen fertilization and the share of infected buds. In trials with no added nitrogen, only a small percentage of buds became infected, while a generous nitrogen application pushed that figure up dramatically — into the tens of percent in some trials, compared with just a couple of percent without any fertilizer at all.

The likely explanation is that heavy nitrogen feeding produces fast, lush but softer growth, which may be more vulnerable to infection, while also extending the period in autumn when new shoots haven't yet hardened off before winter.

Good to know. This doesn't mean fruit trees should be starved of nutrients — a weak, undernourished tree also heals poorly. The takeaway is to avoid one big nitrogen hit, especially late in the season, and instead keep feeding steady and moderate. Our guide to NPK fertilizer walks through how to strike that balance.

How to prevent apple canker next season

You can't make a tree completely immune, but you can make it a much less attractive target. The goal is to reduce the number of open wounds, shorten how long they stay open, and avoid the conditions the fungus thrives in.

• Prune in summer whenever you can. Wounds heal faster while the tree is actively growing, giving the fungus less time to get established before the cut closes. Our guide on pruning apple trees covers the full yearly cycle, not just canker removal.
• Keep the canopy open. An airy canopy dries out faster after rain, which makes it harder for spores to germinate on bark and wounds.
• Plant in well-drained soil. Canker is generally worse on heavy, waterlogged or acidic soils. Improve drainage and soil structure before planting if you know the ground holds water for long periods.
• Protect young trees from frost and rodents. Fresh frost cracks and gnaw damage are common entry points. A simple trunk guard for the first couple of winters cuts that risk noticeably.
• Watch for woolly aphids. Their sugary residue and the wounds they cause can open the door to canker infections. Check branch crotches and old wounds now and then.
• Remove infected wood promptly. The longer a lesion sits, the more spores it produces for the rest of the tree — and the neighbours.
• Avoid a heavy autumn nitrogen feed. The connection to nitrogen above applies especially late in the season, when new growth doesn't have time to harden off before winter.

One prevention method that's rarely mentioned but has shown a real effect in trials is growing especially susceptible varieties under some form of rain cover, such as a simple polytunnel or greenhouse. Fully sheltering trees from rain during the most vulnerable periods has, in research trials, cut infection rates dramatically compared with trees left fully exposed to the weather. That's obviously not practical for a mature tree out in the open, but it's worth considering for young, particularly sensitive varieties grown in containers or a sheltered corner of the garden.

Are some apple varieties more resistant?

Yes, variety does make a difference, even though no variety is entirely risk-free. Much of the resistance data comes from UK trials, so treat it as a general guide rather than a guarantee in every climate — but the underlying pattern tends to hold up well elsewhere too, since it's more about bark and wood characteristics than a specific climate.

If you already have a susceptible variety in the garden, there's no need to dig it up. It just means paying a little extra attention to pruning, drainage and catching early damage, since that tree has somewhat less margin for error than a more resistant one.

Apple canker or something else?

Several other problems on fruit trees can be mistaken for canker, especially from a distance.

If you're not sure, look for the small, reddish or creamy-white fruiting bodies along the edge of the lesion. They're the clearest sign that you're genuinely dealing with canker rather than some other kind of damage.

Can you treat it yourself, or do you need an arborist?

Most cases of apple canker are perfectly manageable yourself with ordinary secateurs or a hand saw, especially if the lesion is on a branch you can reach from the ground or a stable step ladder.

A few situations where it's worth calling in professional help:

• The lesion is high up in a large, mature tree and would require climbing or a lift to reach safely
• You need to remove a major limb or the whole tree, and felling it could damage a fence, structure or power lines nearby
• You're not certain whether the damage is actually canker or something else, and want a second opinion before cutting into a healthy, valuable tree
• Several trees in the garden are affected at once and you want help putting together an overall treatment plan

A certified arborist can also give you an honest read on whether a heavily infected tree is still worth saving, or whether your time and money are better spent replanting. That's a hard call to make objectively about a tree you're attached to.

Common mistakes

• Cutting too shallow. Only removing the visibly damaged tissue, without cutting a margin into clean wood, usually leaves the fungus behind and the lesion returns.
• Composting the prunings. Canker-infected branches can keep producing spores inside a compost heap. Burn them or bin them instead.
• Pruning in the wrong weather. Making a big cut right before a cold, wet spell gives spores ideal conditions to germinate in the fresh wound.
• Over-fertilizing with nitrogen. A heavy nitrogen dose, especially late in the season, makes new growth more susceptible and less hardened for winter.
• Confusing canker with a frost crack. This usually leads to either ignoring a genuine canker lesion or needlessly cutting into healthy wood that only had an ordinary frost split.
• Waiting for the "perfect" pruning season. If an active lesion is spreading toward an important branch, it's better to act now than to wait months for the ideal calendar date.

Frequently asked questions

Is apple canker dangerous to people or pets?
No. Apple canker only affects plant tissue and isn't known to pose any risk to people, pets or other animals. It's primarily a concern for the tree's health and fruit production, not something to worry about from a safety standpoint.

Can you eat apples from a tree with canker?
Fruit that's rotten or comes directly from an infected part of the tree should be discarded, just like any other damaged fruit. Healthy fruit from unaffected parts of an otherwise infected tree is normally fine to eat, but skip anything showing sunken, soft rot.

Does apple canker spread to other plants in the garden?
Yes, it can spread to other susceptible trees, mainly other apples and pears, and occasionally rowan, ash, beech or poplar. It's worth keeping some distance between newly planted fruit trees and heavily infected older ones, and removing infected material so it stops producing spores nearby.

How quickly does apple canker kill a tree?
It varies a lot. A thin branch can die within a single season if it's fully girdled, while a lesion on the trunk of an older, vigorous tree might take several years to become a serious threat. The earlier you spot and treat a lesion, the smaller the chance it becomes life-threatening for the tree.

Can you prevent apple canker without chemicals?
Yes, and in practice that's the only reliable strategy for a home garden, since there's no effective fungicide available to home gardeners. Summer pruning, good drainage, moderate nitrogen feeding, prompt removal of infected wood, and protecting trees from frost and rodent damage together make a real difference.

Are all apple varieties equally susceptible?
No. Some varieties, like Discovery, Katy and Fiesta, are generally considered more resistant, while others, like Cox's Orange Pippin and James Grieve, are known to be more susceptible. The differences are relative, though — even a resistant variety can become infected if conditions favour the fungus strongly enough.

Should you remove the whole tree if the trunk is infected?
It depends on how much of the trunk's circumference is affected. If only part of it is infected, you can often cut out the lesion and let the tree carry on healing. If canker has spread all the way around the trunk — fully girdling it — the tree won't survive and should be removed.

How do I tell apple canker apart from an ordinary frost crack?
A frost crack is usually straight and runs along the length of the trunk, most often on the south or southwest side where temperature swings between day and night are greatest. Apple canker instead produces a more irregular, sunken lesion with concentric rings and small fruiting bodies along the edge. If you're unsure, look for the reddish or creamy-white specks — they don't appear on a plain frost crack.

If you've got more than one fruit tree, it's also worth thinking about how you go about growing apple trees in general and what you prune with — a good pair of secateurs with clean, sharp blades helps wounds close faster and lowers the risk of a fresh infection. Subscribe to our newsletter for more practical guides on keeping fruit trees healthy through the season.