Quaking Aspen Powdery Mildew: Identification and Large-Tree Management

Diagnosis

White residue on aspen leaves (Utah, hot summer) that doesn't wipe off = powdery mildew (fungal). Host-specific—won't spread to other tree species.

Disease Details

• White/gray powdery growth (mycelium + conidia) on leaves, stems, buds.
• Young, succulent growth most affected.
• Leaves may dwarf, curl, deform.
• Late summer = typical timing (humid nights, warm days).
• Overwinters as mycelium or cleistothecia (black specks) on fallen leaves.

Impact Assessment

• Large trees: usually cosmetic, no control needed.
• Severe cases: early defoliation, reduced vigor.
• Fungicides impractical for canopy coverage on mature aspens.

Fungicide Options (If Warranted for Small/High-Value Trees)

Best Practice for Large Aspens

1. Rake/remove fallen leaves off-site (reduces inoculum).
2. Thin dense stands for air flow.
3. Water at base only.
4. Accept cosmetic damage—tree will leaf out normally next spring.