European canker

What you see

An elliptical sunken wound on a branch with the bark cracked and peeled back in concentric rings around a dead centre, often at a pruning scar or bud. Everything beyond it dies. Tiny red-orange pinhead fruiting bodies appear on the canker in winter.

Conditions

Wet, mild conditions and heavy clay or badly drained soil. Spores enter through leaf scars at leaf fall, pruning cuts and scab lesions, mostly between autumn and spring.

Treatment

Cut out cankered wood well beyond the damage, or pare out the canker on a main limb back to clean tissue, in dry weather. Burn or remove the prunings. Copper at leaf fall protects the fresh scars.

Prevention

Choose resistant varieties on well-drained ground. Control scab, whose lesions are a main entry point. Prune in dry weather and clear all prunings from the orchard.

Months: October, November, December, January, February, March

Plants

Apple, Pear, Beech, Ash

Remedies

Bordeaux mixture (copper)

The thing people get wrong

Cankers get pared and painted and then come back in the same place, because the cut stopped at the visible damage. The fungus runs further under sound-looking bark than the sunken area suggests - you have to cut back until the tissue is clean and green all round, which is always further than feels reasonable. On a young tree it is usually quicker to remove the whole limb.