Quaking Aspen Leaf Spot in Utah

The black-spotted leaves and branch dieback on your 5-year-old quaking aspens indicate a fungal leaf spot (likely Marssonina, Septoria, or Cercospora), worsened by wet spring weather.

Symptoms

• Brown/black spots, often with yellow halos.
• Spots merge, leaves yellow and drop.
• Severe cases: near-total defoliation by mid-summer.
• Tree may refush if energy reserves allow.

Management

1. Sanitation (critical): Rake and destroy ALL fallen leaves—spores overwinter on them.
2. Fungicide (next spring): Apply at bud break, repeat 2–3 times at 10–14 day intervals.
   • Chlorothalonil (Daconil)
   • Copper fungicide
   • Mancozeb
3. Cultural: Improve air flow, avoid overhead water, thin crowded stems.

Key Point

Leaf spots rarely kill established aspens directly, but repeated severe defoliation weakens trees, inviting cankers and borers. Break the cycle with sanitation and spring protection.

Colorado State Extension link in original has excellent photos for comparison.