Many insects and disease concerns exist throughout the Steamboat Springs area.

Common Insect & Disease Concerns

Bark Beetles

Bark beetles are insects that feed on the cambium (the layer beneath the bark) of trees. Most bark beetles breed in trees that are severely stressed or dying. A few beetles are capable of killing trees, either through mass attacks and/or through the introduction of disease causing-fungi. The two most critical beetles in the Steamboat Field Office area are mountain pine beetle and spruce beetle.

Mountain pine beetle (MPB) is prevalent throughout Jackson and Routt counties. MPB only affects larger (i.e., >8 inches in diameter) mature lodgepole pine or ponderosa pine trees.

Signs & Symptoms

  1. Popcorn-shaped masses of resin (pitch tubes) on the trunk
  2. Reddish boring dust in bark crevices or adjacent to the tree base
  3. Reddish needles (Crowns of successfully attacked trees usually turn off-color beginning in May or June following the previous summer’s attack.)

Control & Prevention

  • Maintaining a healthy, vigorous tree or stand is critical
  • Natural controls include woodpeckers and a few insects (limited application during high levels of attack)
  • Infested logs can be treated in various ways to kill developing beetles:
    • Burning, removing bark, burying or intense solar radiation
    • Chemical options, unfortunately, are greatly limited. Prevention options are limited to carbaryl (Sevin) and permithrin (Astro). Apply to high value living trees in early summer prior to beetle emergence

Spruce beetle (SB) is similar to mountain pine beetle in all aspects expect one — spruce beetle differs typically prefer blowdown material. Under normal circumstances they don’t attack live trees.

Additional Information

White Pine Weevil

White pine weevil can be the most serious insect pest to Colorado blue spruce in landscape plantings. The insect larvae feed underneath the spruce leader, girdling the plant and causing a stunted top. Once the top leader is killed some side branches will begin growing skyward to replace the old terminal leader. If this occurs, train the best one by removing other competing branches so that only one new terminal leader remains.

Insecticides applied in the spring when the weevils feed and lay eggs can provide control for that year. Standard bark beetle or wood borer insecticides (Sevin, Dursban, Astro) applied at the recommended rates should provide control. Application will need to occur annually to prevent annual attacks.

Additional Information

White Pine Weevil Insect and Disease Leaflet

Poplar Borers

Poplar borers primarily affect aspen, but cottonwood and poplar can also be hosts. Damage is associated with moist bark areas and is generally indicated by the presence of sawdust, a result of the insect tunneling into the sapwood. Chronically infected trees exhibit a black varnish-like stain on the bark below points of attack.

Control: Because of the long life cycle, poplar borer is difficult to control. Standard borer treatment of insecticides (Sevin) applied to the trunk should provide coverage throughout the activity. Application to existing areas of attack (where egg laying is concentrated) should be thorough.

Additional Information

Shade Tree Borers Fact Sheet (244 KB PDF)

Aspen Leaf Spots

Several types of fungi can cause spots on aspen leaves. None of these are detrimental to aspens unless several consecutive years of defoliation occur. The best method of control and prevention is by removing the infected leaves on the ground to reduce available spores for future spread.

Additional Information

Leaf Spot Fact Sheet (203 KB PDF)

Other Insects and Diseases

Many other insects and diseases naturally occur throughout Colorado. Please check out the following links for additional information: