Stem canker
Sunken, dead patches of bark on stems and branches caused by fungi or bacteria, which can girdle and kill the shoot above them.
Also known as: Canker, Branch canker
Symptoms and identification
Sunken, cracked or discoloured patches of bark appear on branches or stems, often reddish-brown or black and sometimes oozing sap. Leaves above the canker wilt, yellow and die back. Small pimple-like fungal bodies may appear on the dead bark.
Causes
Cankers usually start where bark is damaged by pruning cuts, frost, sunscald, hail, mowers or insects. Stressed plants, drought, waterlogging and overfeeding make attack more likely.
Organic treatment
Cut out cankered branches at least 10 to 15 cm into healthy wood, disinfect tools between cuts and bin the cuttings. Do not use wound paint.
Prevention
Prune in dry weather with clean, sharp tools, avoid wounding bark, protect young trunks from frost and sunscald, and keep plants watered and fed evenly through the season.
Chemical treatment (use with care)
There is no cure for existing cankers. A copper spray in autumn can help protect fruit trees from some bacterial and fungal cankers, following the label.