Introduction:
Rose cankers appear any time of year but especially when the plants are under stress. Three canker diseases (brown canker, stem or common canker, and brand canker) are common in Illinois and are generally confused with weather injury or other problems. Cane infections may approach 100 percent (all canes infected) where control measures are not practiced. Identifying particular canker species is not important, but it is important to identify a problem as a canker.
Causal Agent:
Coniothyrium spp
Symptoms:
- The first symptoms are small, roundish lesions in the canes the spots are pale yellow, reddish, or bluish purple.
- They gradually enlarge, turn brown or grayish white (often with a darker margin), and may partially or completely girdle the cane.
- Complete girdling results in dieback or poor growth of the plant parts above the affected areas.
- Cankered areas are sprinkled with black, speck-sized, fungus-fruiting bodies.
- When left unchecked, infections may spread downward into the crown, causing entire rose plants to wilt, wither, and die.
- Infection occurs chiefly through a wide variety of wounds, including thorn abrasions. Infections may also occur on the leaves and flowers.
Disease cycle:
The fungi causing stem canker and die back usually survive the winter on diseased canes or plant debris. Spores of the causal fungi are usually spread by wind-blown rain or irrigation water. Rose canes are infected through wounds during periods of humid, wet weather. The disease may also be spread by fungus-contaminated pruning tools. Cankers often form on the stub of pruned canes, but they may also be seen around leaf or thorn scars, winter injury, or other damage on the canes. Stem canker and dieback are most damaging to weak, slow-growing roses.
Control:
- Removal of the infected cane or canes to good clear cane tissue below the canker followed by the spraying of a good fungicide will help in getting rid of or reducing the canker problem.
- Remember to wipe off the pruners with the disinfectant wipes or dip them in the Clorox solution after each pruning of a diseased cane.
- Always wipe down your pruners with Clorox or Lysol disinfectant wipes or dip them into a mixture of Clorox and water before pruning each rose bush.
- Promoting vigorous growth helps as well, as a healthy thriving rose bush fights off the canker attacks well. Using a good preventative fungicidal spraying program goes a long way to not having to deal with the frustrations of a fungal infection and the elimination of it.
- A rotation of fungicidal sprays is recommended to help keep the different funguses from becoming resistant to the fungicides effects.
- As stated above, keep canes from crossing each other. Even if they appear not to be touching, wind and growth can change that condition.
- Pruning out dead or dying wood during your regular visits to the garden is also essential.
- when planting new plants, use care not to damage canes. If you should damage a cane seriously, consider removing the cane entirely.
- Likewise, when pruning or deadheading, cut back to the node. Failing to do so, results in dieback to the node, and the resulting dead wood is an invitation to canker spores.
- As for fungicides, those that control black spot on ornamentals will also control canker.
Favorable conditions:
- Wet weather
- Humid conditions
- Low plant to plant distance
- Less air circulation
Also Study: Black Spot of Rose | Symptoms | Survival and Dispersal Management