The weather this summer has resulted in many peonies catching the “measles.” This is a disease, also known as red spot, that causes distinct, reddish-purple spots on the upper leaf surfaces. These spots often coalesce and become large, reddish purple blotches on the upper leaf surfaces but are a light brown color when viewed from the underside of the leaves. The spots on stems will merge and form streaks that are reddish brown.
Sanitation is the best control for this disease. Remove all diseased tissue, including stems, at the end of the growing season.
Mulch that contains plant debris should also be discarded and then replaced with fresh mulch. Reducing the source of the inoculum will reduce the chances of another severe outbreak next year. (Ward Upham)
