Stem Canker on Roses

Brown Canker

• Brown canker first appears as small reddish to bluish-purple spots on new cane growth. As the spots enlarge they become grayish white at their centers with reddish purple edges. As the disease progresses spots coalesce to form whitish tan blotches with purple edges. During winter and early spring the tan splotches enlarge and become surrounded by brown variegated cankers that can girdle the stem causing dieback.

Stem or Common Canker

• This fungus usually appears at the site of a wound first as yellow to reddish spots. As the spots increase in size they become light brown with dark brown edges. The tissue within the canker dries out and often stems will crack as the disease progresses. Inside the cracks are sooty masses of spores. Stems may ultimately be girdled resulting in dieback from the tip to the infected portion.

Brand Canker

• Dark reddish spots first appear around wound sites, such as an insect bite. As spots enlarge they turn light brown with definite reddish-purple edges. As fruiting bodies within the canker enlarge they cause dark longitudinal slits in the stem that are characteristic of brand canker. As cankers enlarge, they can girdle stems and cause dieback.

Control

• Fall pruning is recommended to prevent wind-whipped canes from injuring each other during the winter. Cut out any dead or diseased stems first. Haul away or burn any diseased debris removed from the plant to prevent re-infection. Prior to each cut dip your shears in a solution of bleach and water at a concentration of 1 part bleach to 10 parts water. Fungicides are recommended in conjunction with insecticides and miticides as wounds caused by pests are often primary infection sites.