Canker

Neonectria ditissima, with Nectria and Cytospora spp.

also called Apple canker, Nectria canker

Sunken, cracked patches of dead bark that can girdle and kill branches. Prune back to clean healthy wood in dry weather and improve tree vigor.

Fungus Serious Rain splashAirborne sporesSpread on tools & hands Spreads to neighbors

What you'll see

An oval sunken patch of dead, discolored bark that cracks into concentric rings as the wood beneath shrinks.
A swollen lip of new callus around the edge where the tree has tried and failed to grow over it.
White pinhead pustules in summer and tiny red-orange fruiting bodies in winter around the dead area.
Growth above the canker is weak and leaves are small; if it goes right round the branch, everything beyond it dies.
Fruit on affected branches may rot at the eye or in store.

Why it happens

Fungi that enter through wounds — pruning cuts, leaf scars, frost cracks, scab lesions, woolly aphid damage — and then kill the bark and cambium outward from that point. Spores are released mostly in wet autumn and winter weather and splash onto fresh leaf scars. Trees already under stress cannot wall the infection off.

Heavy, wet, poorly drained soil and a cold damp autumn are the classic setting. Susceptible cultivars, waterlogged roots and a badly timed prune in wet weather all speed it along.

Treating it

Cut out affected wood in dry weather, back to clean, unstained tissue — take the whole branch off at a junction where you can.
On a trunk or a limb too big to lose, pare away the dead bark and a margin of healthy bark with a clean knife and let the wound dry in the open air.
Sterilize tools between cuts and burn or bin every scrap of cankered wood.
Improve the tree’s vigor: relieve waterlogging, mulch, feed sensibly and thin a heavy crop.
Do not paint wounds with sealants — they trap moisture; leave the cut clean and open.

Keeping it away

Plant resistant cultivars on well-drained ground; Cox, Spartan and Gala are among the worst affected apples.
Prune in dry weather, ideally midsummer for stone fruit and dry winter days for apples and pears.
Make clean cuts to the branch collar with no stubs, and keep tools sharp.
Control scab, woolly aphid and anything else that wounds the bark.
Improve drainage before planting rather than after the first canker appears.

Who gets it

Apples and pears most of all, with plums, cherries, poplars, willows and many ornamental trees having their own cankers.