Remove spotted leaves when seen. No chemical control is listed. Leaf spots may be caused by several fungi, however few of these fungi will be seen. No chemical control is listed.
Powdery mildew causes a white coating on the leaves.
Applications of sulfur or benomyl control the 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.