Canker of Rose

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Dr. John F. Baniecki
WVU Extension Service
Plant Pathology and
Entomology Specialist
August 2000

There are three stem or cane cankers common on roses: Brand Canker, Brown Canker and Stem Canker.

Key For Identifying Canker Diseases of Roses

Brand Canker (Coniothyrium wernsdorffiae)

Common on rambler-type roses. The center of the lesions are light brown with a border of reddish-brown or purple. This border is usually surrounded by a more indeterminate reddish area. Minute elevations of the fungus fruiting bodies appear in the brown center, with longitudinal slits later appearing that expose black masses of spores.

 

Brown Canker (Diaporthe umbrina).

Common on most rose varieties. Purple to white spots on the canes and small dark gray, circular spots on the upper surface of the leaves. Smal cane lesions are slightly raised, circular, purple and quite superficial. Lesions later become grayish-white. The massing together of these tiny spots produces a whitish patch that later is surrounded by a purple margin. Lesions continue to enlarge until the cane is girdled and destroyed, leaving a brown dead area.

 

Stem Canker (Leptosphaeria coniothyrium)

First appears as pale yellow or reddish spots on bark of the cane. Spots enlarge and grow together, resulting in large infected areas on which small, black, fruiting bodies of the fungus may be found. Cankers may girdle entire stem, causing wilting and death of the parts above, or they may spread up one side of the stem, causing browning and cracking of the bark but not immediate death; however, a weak, one-sided plant results. More prevalent on hybrid tea roses.

Control Measures

Brand Canker -Can be controlled almost entirely by leaving roses uncovered during the winter. Prune out and burn infested canes. Do this as soon as the cankers are discovered.
Brown Canker -Select disease-free planting stock. Prune out and burn all infected parts. The fungicides used for black spot control will usually control this disease.
Stem Canker -Prune out and burn all infected canes. The fungicides used for black spot control will help control this disease.

Note: When cutting out the cankers, be sure to make the cuts well in back of the cankered area. Disinfect pruning shears after cutting by dipping them in alcohol.