University of Maryland Extension

Botryosphaeria Canker - Shrubs

canker on a shrub
 Botryosphaeria Canker, (Botryosphaeria dothidea)

Botryosphaeria canker is the most common disease of rhododendron in the landscape. A typical symptom of this fungal disease is scattered dying branches on an otherwise healthy plant. Leaves on infected stems droop and roll inward, then turn brown. These leaves often lay flat against the stem and will remain attached. The pathogen can infect all ages of stem tissue through wounds, pruning cuts, and leaf scars. Heat, drought stress, and winter injury can increase disease incidence. Cankers on branches can gradually grow through the wood until the stem becomes girdled. Diseased wood is reddish brown in appearance. Discolored wood viewed in a longitudinal cross section often forms a wedge that points toward the center of the stem and the pith may be darker brown than the surrounding wood.

close up of a canker
Close up of canker.  Photo credit - G Moorman, PSU


Fungicide treatments are not an effective disease control option. Plants should be grown in partial shade, with mulch and kept well watered during dry periods. All dying branches should be promptly pruned out in dry weather and all discolored wood should be removed. Plants should also be protected from rough treatment during maintenance activities to prevent unnecessary wounds.

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