Insects and diseases pose two of the most serious threats to a tree's health. As soon as any abnormality is discovered in a tree's appearance, measures should be taken to diagnose the problem.

2015 Aerial Insect & Disease Survey in Colorado

On Jan. 28, 2016, the Colorado State Forest Service and U.S. Forest Service (USFS), Rocky Mountain Region, released the results of the 2015 forest health aerial survey for Colorado.

Every year the USFS and CSFS work together to aerially monitor forest health conditions on millions of forested acres across the state. Monitoring forests to assess the status of damaging insects, diseases and other pests is an integral part of forest management. Aerial survey observations of tree-damaging insects and diseases native to Colorado’s forests are highlighted below.

Insect & Disease Activity in Colorado Forests, 2015

2015 Insect & Disease Activity in Colorado Forests

Survey Highlights

Spruce Beetle in and near Rocky Mountain National Park
Spruce Beetle in and near Rocky Mountain National Park (click on map for pdf)

Spruce beetle outbreaks caused widespread tree mortality for the fourth consecutive year

  • Spruce beetle populations have expanded, impacting higher-elevation stands of Engelmann spruce.
  • In 2015, spruce beetle infestations were detected on 409,000 acres across the state, expanding onto 182,000 acres of previously unaffected forests.
  • Since 1996, spruce beetle outbreaks have caused varying degrees of tree mortality on more than 1.5 million acres in Colorado.
  • Blowdown events, combined with long-term drought stress, warmer temperatures and extensive amounts of older, dense spruce, have contributed to this ongoing epidemic.
Spruce Beetle and Western Spruce Budworm, Southern Colorado
Spruce Beetle & Western Spruce Budworm, Southern Colorado (click on map for pdf)

Outbreaks of two defoliators of conifer trees – western spruce budworm and Douglas-fir tussock moth – expanded in 2015

  • The area impacted by western spruce budworm, Colorado’s most widespread forest defoliator, increased from 178,000 acres in 2014 to approximately 312,000 acres in 2015. This insect typically feeds on developing buds and new needles of fir, Douglas-fir and spruce in southern Colorado.
  • Douglas-fir tussock moth caterpillars consumed needles on Douglas-fir, white fir and spruce on approximately 26,000 acres along Colorado’s Front Range. Impacts were observed primarily in the South Platte River Basin and areas just west of Colorado Springs. Ground surveys have documented the presence of a naturally occurring virus among Douglas-fir tussock moth caterpillars, which has historically been a key indicator of imminent population collapse.
  • Trees weakened by these defoliators may become susceptible to Douglas-fir beetle, which can kill impacted trees.

Mountain pine beetle activity has subsided and remains low, with 5,000 acres affected statewide. The epidemic has ended in many areas of Colorado as mature pine trees have been depleted in the core outbreak areas.

For more details about the 2015 aerial survey, visit the U.S. Forest Service, Rocky Mountain Region at

By examining specific symptoms of insect or disease damage, you can make a reasonable diagnosis of the problem and select the proper treatment. If you are uncertain about the type of insect or disease or do not know how to treat them, contact your local CSFS Field Office to conduct a homesite assessment of the trees on your property.

Learn More About Insects & Diseases in Colorado