Powdery Mildew on Lilacs and Peonies: Common, Manageable

White powdery substance on lilac and peony leaves.

Identification

Powdery mildew—superficial white/gray fungal growth on leaves, stems, flowers. Patches enlarge, cover leaves. Young growth susceptible. Curling/twisting precedes visible fungus. Severe cases: yellowing, browning, distorted shoots. Rarely fatal but unsightly.

Host Specificity

Each powdery mildew species has limited host range. Lilac mildew doesn't spread to peonies or roses.

Conditions

Favored by 60-80°F, high humidity, overcrowding, shade. No free water needed for germination.

Control

Often ignorable on lilacs (yearly, minimal health impact). For control: fungicides at first detection, regular schedule, spreader-sticker, both leaf surfaces. Options: Triadimefon, Triforine, Thiophanate-methyl, Propiconazole.