Many of the powdery mildew fungi will grow on only one side of the leaf, usually the top, but some show no preference and will grow on both sides. The powdery fungal growth may completely cover the leaf, or may be limited to a defined patch. The leaves may become yellow and curl if the infection is heavy. In some cases, a yellow or dead patch will appear on the leaf, usually on the upper surface, while the white powdery growth is on the lower surface. Flowers and fruit may become distorted, and leaves, flowers, or fruit may die in very severe infections.
Plants often recover if the disease is controlled early enough.
Tiny black dots may be barely visible in the fungal growth, usually in the late season. Powdery mildew on verbena. D. Kerbow photo. Powdery mildew on rose. D. Kerbow photo.