Avoid infested soil. No chemical control is listed. Bacterial spot causes spots on leaves. Remove and destroy infected leaves as noticed and cut and discard old stems in the fall. No chemical control is listed.
Powdery mildew causes a white powdery growth on the leaves.
Applications of benomyl or sulfur control this problem. This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information becomes public property upon publication and may be printed verbatim with credit to MSU Extension. Reprinting cannot be used to endorse or advertise a commercial product or company.