Powdery Mildew on Lilac: Identification and Treatment

The white, ash-like coating on your new lilac leaves is classic powdery mildew (Microsphaera syringae), a common fungal disease on lilacs, especially in humid, shady, or crowded conditions.

Symptoms

• White to gray powdery patches on leaf surfaces (upper and lower).
• Leaves may curl, distort, or drop prematurely.
• Young shoots and flower buds can be infected.

Treatment

1. Fungicide spray at first sign. Effective homeowner options:
   • Myclobutanil (Spectracide Immunox)
   • Propiconazole (Bonide Infuse)
   • Chlorothalonil (Daconil)
   • Sulfur (Safer Garden Fungicide)—apply before 85°F.
2. Cover all leaf surfaces thoroughly. Repeat per label (usually 7–14 days).
3. Prune for air flow—thin crowded stems after bloom.

Prevention

• Plant in full sun with good air circulation.
• Avoid overhead watering.
• Choose resistant cultivars: 'Miss Kim', 'Palibin', 'James Macfarlane', 'Betsy Ross'.
• Rake and destroy fallen leaves in fall.

Your lilac should recover with treatment and better conditions next year.