Looks like powdery mildew (a mold) to me. remove all the affected leaves and bag them to the curb. Be sure to inspect all the other leaves for any beginning signs of infection too.
List of Bryant RedHawk's Epic Soil Series Threads We love visitors, that's why we live in a secluded cabin deep in the woods. "Buzzard's Roost (Asnikiye Heca) Farm." Promoting permaculture to save our planet.
Yeast devil! Back to the oven that baked you! And take this tiny ad too: