Bacterial canker

What you see

Sunken, dark, elongated patches on branches oozing amber gum, with the leaves above them wilting and the branch dying back. Leaves may show small spots whose centres drop out. Whole limbs can be lost in a season.

Conditions

Cool wet weather in autumn and spring. It enters through leaf scars at leaf fall and through pruning wounds - which is exactly why winter pruning of stone fruit is a mistake.

Treatment

Cut affected limbs well back into clean wood, in dry summer weather only, and disinfect the saw between cuts. Copper at leaf fall protects the fresh leaf scars.

Prevention

Prune stone fruit only in mid-summer, never in winter. Keep trees well fed and unstressed. Protect from wind rub. Avoid planting into cold, wet, poorly drained sites.

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

Plants

Cherry, Plum, Apricot, Peach, Nectarine, Almond

Remedies

Bordeaux mixture (copper)

The thing people get wrong

The rule that stone fruit is pruned in summer, not winter, exists entirely because of this disease and silver leaf - and it is the rule most often broken, because winter is when the tree is bare and pruning feels natural. Every winter cut on a plum or cherry is an open wound during exactly the wet cool months when the bacteria are active.