A canker disease attacks blooming plants. Dark brown lesions form on the branches at the nodes, these later turn ash gray. As the spots enlarge and girdle the stem the parts above wilt and die. Remove and destroy infected plants when seen and destroy plant residues in the fall.
Leaf spots may be an occasional problem. Remove and destroy spotted leaves.
Powdery mildew coats the leaves and small branches with a white powdery growth. This disease can be controlled with sprays of benomyl.