See:
Rose (Rosa spp.) and hybrids - Brand and Common Canker
Cause The fungus Cryptosporella umbrina has been reported only from Idaho. The disease is more common in the Southeastern United States. High moisture environments (such as hilling for winter protection) favor the disease. Spores can penetrate uninjured tissue. Lesion can form after 10 days under favorable conditions.
Symptoms Small red-to-purple spots appear on current season canes. Spots enlarge into whitish necrotic lesions with reddish-purple borders during the winter months. Cankers may coalesce and can be several inches long. Small black pycnidia can be seen in the cankered area. Cankers can wilt and kill distal portions of the cane. Easily confused with other canker diseases such as Brand or Common Canker.
Cultural control
- Prune canes with a sharp knife or pruner immediately above a node when first symptoms are noticed.
- Remove and destroy canes before sporulation occurs.
- Use a winter protecting mulch that does not hold much water such as sand, rock pumice, or coarse bark.
Chemical control Usually unnecessary if cultural controls are used. Ineffective once canker symptoms are seen.
Reference Pscheidt, J. W., and Rodriguez, T. G. 2018. Diseases of Rose. In McGovern, R.J. and Elmer, W.H. (eds.) Handbook of Florists' Crops Diseases. Springer Int.