Common Insects & Diseases of Aspen


Aphids are small insects that feed by sucking plant sap from leaves and excrete a sweet, sticky substance called honeydew. The damage is mostly unsightly but, in the long-term, may kill the branches they feed on.

Aphids on Shade Trees and Ornamentals Fact Sheet (43 KB PDF)

Ink Spot Disease

Ink spots are a result of the fungus Ciborinia and are commonly found in dense aspen stands. This disease causes leaf discoloration and early leaf drop, which may reduce tree growth.

Aspen and Poplar Leaf Spots Fact Sheet (203 KB PDF)

Marssonina Blight

The Marssonina fungus causes this most common disease on aspen foliage. Although there is leaf discoloration, this condition usually is not damaging. Heavy infestations cause early leaf drop.

Aspen and Poplar Leaf Spots Fact Sheet (203 KB PDF)

Aspen Leaf Miners

Adult leaf miners cut tiny slits on aspen leaves and lay their eggs inside. The larvae live inside the leaf and feed by "mining" chlorophyll from plant cells; this is not harmful to the tree's health.

Leaf Miners Fact Sheet (128 KB PDF)


Sawflies are closely related to wasps. The larvae are plant feeders and look like hairless caterpillars. Sawflies often feed in groups and can quickly defoliate portions of their host plant.

Elk Scarring

Elk browse on the shoots and stems of aspen trees, creating wounds and allowing the introduction of diseases.

Western Tent Caterpillar

This defoliating caterpillar feeds on the leaves of aspen, causing aesthetic damage. Consecutive years of defoliation, however, may kill the tree.

Tent Caterpillar Fact Sheet (88 KB PDF)

Oystershell Scale

Scale, a common and destructive pest, overwinter on trees and harm them by sucking sap. Branch and tree death are possible with long-running infestation.

Oystershell Fact Sheet (78 KB PDF)

Poplar Twiggall Fly

These common galls are caused by tiny black flies. While they will continue to grow years after they are produced, they do not threaten the health of the tree.

Poplar Twiggall Fly Fact Sheet (144 KB PDF)

Blank Canker

This slowly developing canker is caused by the fungus Ceratocystis fimbriata and is easily recognized. The canker rarely kills the tree due to its slow development.

Sooty Bark Canker

Sooty bark canker is caused by the fungus Encoelia pruinosa and is the most lethal canker on aspen in Colorado. The dead bark falls off and exposes the crumbly black, sooty inner bark.

Epidermal Bark-Mining Fly

This curious spider-shaped track is made by the larvae of a fly and is not harmful to the health of the tree.

Trunk Rot

Phellinus igniarius decay fungus enters through old branch stubs or other wounds. Affected trees often are used by hole-nesting birds.

Poplar Borer

This wood-boring beetle lays eggs on the bark of the aspen. The larvae then tunnel, weakening the wood. Entry and exit holes of the beetle invite fungi, which can result in limb breakage.

Shade Tree Borers Fact Sheet (244 KB PDF)

Keeping Your Aspen Healthy

  • Maintain a proper watering schedule – aspen will suffer if over- or under-watered.
  • Prevent direct sprinkling of leaves by lawn watering systems.
  • Unwanted aspen sprouts that appear in the lawn may be mowed. DO NOT spray the sprouts, as they are connected to the mother tree.
  • Avoid wounding the main trunk with movers or weed wackers.
  • Trim out cankers that are less than half the circumference of the aspen.
  • Clean up heavy scale-insect infestations.

What's Ailing Your Aspen? Poster (935 KB PDF)

2009 Report on the Health of Colorado's Forests - page 24 (7 MB PDF)