Cytospora canker: how to recognise and treat it

Disease

Cytospora canker — Photo: Curtis Swift, CC0, Wikimedia Commons

Symptoms

Gum oozes from the bark around the infection on stone fruit trees.
Sunken dead patches of bark that stretch along the branch more than across it and grow year after year.
Leaves above the canker droop and turn brown but stay attached, sometimes through winter.
Pinhead-sized black pimples in the dead bark release amber to orange spore threads.

Organic treatment

Cut out dead branches well below the canker, at least 30 cm past any discoloured bark.
Prune during or after bloom, when growing trees can defend the cuts; wound dressings do not help.

Chemical treatment

Captan or thiophanate-methyl on fresh pruning wounds protects them before infection; no fungicide cures an existing canker; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Avoid bark wounds, because the fungus enters through cold-injured wood and pruning cuts.
Keep trees vigorous and avoid conditions that stress them.
Plant winter-hardy cultivars on a well-chosen site.

Plants it affects

Sources

Figures checked against these sources.