Aspen Leaf Spot: Fungal Disease in Colorado Springs

Marssonina Leaf Spot Identification and Control

Black, crusty leaf edges on aspens in Colorado indicate Marssonina leaf spot, favored by wet spring weather. Lesions are brown with yellow margins. Severe cases cause defoliation.

Management

• Increase vigor: deep watering and fertilization.
• Fungicides (chlorothalonil or fixed copper) at bud break, repeat every 10–14 days in wet weather.
• Avoid sprinkler irrigation on foliage.
• Rake fallen leaves (limited benefit due to airborne spores).

Vigorous trees often outgrow the disease without sprays.