Canker Fungus On Rose Bush
(Image credit: Stan V. Griep)

Rose canker is also known as Coniothyrium spp. This is the most common of the several kinds of rose canker fungi that can affect the canes of roses. When left unmanaged, not only can rose cankers eat away at the beauty of your rose bushes, but they can eventually kill your rose plant.

Identifying Rose Canker Fungus

Rose canker is what is known as pathogenic fungi, while it is not really all that complicated a fungus, it can still cause a lot of damage. Rose cankers will often show itself as black splotches on the canes of rose bushes.

Many times after a recent pruning, rose stem cankers will show up, especially when the pruners have not been cleaned between the pruning of different rose bushes. Rose canker can spread from a rose bush where it was just pruned out to an uninfected rose bush by using the unclean pruners.

Canker is most active during cold times of the year when rose bushes are less active.

Preventing And Curing Rose Canker

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 fungi from becoming resistant to the fungicide's effects.

Stan V. Griep

Stan V. Griep contributed to Gardening Know How for many years. An American Rose Society Consulting Master Rosarian in the Rocky Mountain District, he served as Gardening Know How's in-house expert on all things roses.