Brown canker appears as light brown lesions with deep purple margins. This fungus will also attack foliage and buds on some cultivars. It is not common if a fungicide program is followed for control of other rose diseases. Stem canker appears as black spots, often at the point of mechanical damage. It is somewhat reddish and becomes brown, sunken and cracked with age.
Cankers often appear on plants weakened due to black spot.
The most effective means of preventing the problem is to maintain a preventive fungicide spray program to control other fungal diseases. Should cankers appear, prune the cane well below the canker with clean pruning shears. Prolonged rainy periods are not favorable for spore germination because it is inhibited by standing water. The disease first appears as a whitish-gray, powdery coating at the tips of canes. Young leaves often become culled, distorted and dwarfed.