As we approach pruning season, you’ll be looking more closely at your roses, and you may encounter rose canes that appear darkened or dead. Likely, this is dieback, a condition characterized by the progressive death of stems and canes that can ultimately compromise the health and appearance of your rose plants. The dying areas may appear on the outer portions or the terminal areas of the cane, usually extending down from the tips of stems or canes. It can be isolated to a small section of a cane, like a portion left above a pruning cut, or an entire cane, down to the bud union. Dieback can occur any time of the year and is found wherever roses are grown.
In roses, this malady may be caused by various factors both living and environmental. Fungal species like Botryosphaeria produce cankers that cause tissue death. Flatheaded borers, Chrysobothris spp., may kill canes or an entire plant. The raspberry horntail, Hartigia cressoni, cause tips of canes to wilt and die in spring, reducing second cycle blooms. Stressors like improper pruning, extreme weather, and poor soil health can weaken the plant’s immune system, making it more susceptible to diseases. And it may simply be a result of age – a cane’s productivity will diminish over time with its coloring changing from greenish-gray to yellow to brown.
If dieback has already affected your roses, prune out all the infected parts, down to a point that you see healthy green pith. Make your cuts with sharp shears well below the diseased areas. After cutting out the cane, and before proceeding to another, sanitize your pruners by dipping the blades into a mild bleach solution (one part bleach to nine parts water) between each cut. Make sure to dispose of all material; don’t add it to your compost pile.
To prevent, or at least minimize the occurrence of dieback:
- Buy disease-free plants from a reputable nursery
- Keep plants in good health with adequate sun, water, and air circulation
- Grow in organics rich, well-draining soil
- Maintain good garden sanitation
- Prune carefully using sharp pruners leaving a clean, sloping cut just above nodes; don’t leave long stubs
By Nanette Londeree, Master Rosarian