Rose canker is usually the result of careless pruning or breaking of stems. Dark reddish lesions and cracking bark of rose canes are symptoms of rose canker.

They are caused by a fungus that enters through pruning cuts or wounds to the shrub. Cankers can encircle stems and cut off the flow of nutrients and water to growth further up.

Control:
Prune off and burn diseased canes. Canker can be spread from plant to plant by infected secateurs.

Make a neat slanting cut to just above a good outward-facing bud and disinfect secateurs often.