See:
Rose (Rosa spp.) and hybrids - Brown Canker
Cause Two fungi. Coniothyrium wernsdorffiae causes brand canker, and Paraconiothyrium fuckelii (formerly Coniothyrium fuckelii) causes common canker. Both infect cane wounds caused by pruning, harvesting, insects, thorn scars, or scratches. Contaminated cutting knives, scissors, or pruners are a major source of the pathogen. Cool winter temperatures and winter coverings that keep canes moist favor brand canker. Common canker is favored by improper pruning, especially leaving long stubs above the last node. Common canker lesions developed more rapidly on young succulent stems than on older canes. High nitrogen fertility also increased common canker size.
Symptoms The diseases are easily confused. Both start out as discolored (yellow to red) spots that gradually enlarge with the center turning light brown. In cut-flower production, the cut stem turns yellow-to-black as the pathogen advances into the tissue. Brand canker develops a reddish-brown or purple margin that contrasts sharply with the normal green rose cane. Common canker has a darker brown margin and generally develops at the cane's cut end. Both cankers develop small black fruiting bodies (pycnidia) toward the center of damaged tissue. Brand canker that develops under the snow line will at first in spring be black, but then it develops as described above after being uncovered several weeks. Cankers may girdle stems, causing stems and shoots above that point to wilt and die. The disease is easily confused with Brown Canker.
Cultural control
- Avoid injuring canes.
- Prune canes with disinfected, sharp knife or pruner immediately above a node. Avoid leaving long stubs above a node.
- Frequently clean and disinfect cutting tools.
- Cut and destroy infected canes well below the affected area.
- Use a winter protecting mulch that does not hold much water such as sand, rock pumice, or coarse bark.
- Use a balanced fertilizer with moderate nitrogen.
Chemical control Usually unnecessary if cultural controls are used. Ineffective once canker symptoms are seen.
Reference Intrama, S. 1968. Coniothyrium rose canker in Oregon. PhD thesis, Oregon State University. pp 95.