Unsightly, but not serious. Especially in shaded areas. This disease is not damaging. Ignore this disease or, when mildew first appears, apply fungicide at 10-day intervals. Use chlorothalonil, copper-containing fungicides, myclobutanil, propiconazole, sulfuror triadimefon.
Some species are more resistant .
University Outreach and Extension does not endorse commercial products. Follow the label on all pesticides.