How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

In fall or spring European canker causes reddish brown lesions to appear on small branches just below leaf scars. These elongate into cankers with concentric ridges and may cause dieback of shoots in spring. Calyx rot of fruits can occur in years when rain precedes harvest. Pruning wound infections are seen occasionally (especially on the Delicious cultivar). On superficial examination, such infections may be confused with fire blight.

COMMENTS ON THE DISEASE

This fungus survives in old bark cankers and produces spores that enter fresh leaf scars during fall rains. The Delicious variety is most susceptible, followed by Gravenstein and Rome Beauty. This disease is worse in the Sebastopol area of Sonoma County in years with prolonged fall rains.

MANAGEMENT

European canker is managed primarily by pruning and protectant fungicides. Cankers should be pruned out of trees as they ultimately kill branches and also serve as sources of inoculum. Prune and burn diseased wood early in summer. At this time symptoms are obvious and spread of the fungus is not likely. Because infection occurs through leaf scars and leaves fall over a long period, two treatments are necessary each fall to protect new leaf scars.

Organically Acceptable Methods
Treatments with Bordeaux or approved fixed copper materials are organically acceptable.

Treatment Decisions
If European canker is damaging your orchard, apply a freshly prepared Bordeaux mixture of 10:10:100 or a fixed copper material at label rates during early leaf fall, before rains begin. Where the disease is serious, make a second application when three-fourths of the leaves have fallen.

PUBLICATION

UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Diseases
W. D. Gubler, Plant Pathology, UC Davis
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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