Common Forest Insects & Diseases

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.

By examining the specific symptoms of damage and understanding their causes, 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 forester to conduct a homesite assessment of the trees on your property.

2012 Forest Health Aerial Survey Results

Click on the 2012 Insect and Disease Activity map to view a full-size version (164 KB PDF).

On Feb. 6, 2013, the U.S. Forest Service and Colorado State Forest Service released the results of the annual aerial insect and disease survey in Colorado.

The survey indicates that the spread of the mountain pine beetle epidemic has slowed dramatically, while the spruce beetle outbreak is expanding.

Mountain Pine Beetle

Click on the 1996-2012 Forest Insect and Disease Progression map to view a full-size version (205 KB PDF).
  • The mountain pine beetle epidemic expanded by 31,000 acres, down from last year's reported increase of 140,000 acres.
  • This brings the total infestation to nearly 3.4 million acres in Colorado since the first signs of the outbreak in 1996.
  • Most mature lodgepole pine trees have now been depleted within the initial mountain pine beetle epidemic area.
  • However, the infestation remains active from Estes Park to Leadville.

Spruce Beetle

  • In contrast, the spruce beetle outbreak is expanding, with 183,000 new acres detected in 2012.
  • This brings the total acreage affected since 1996 to nearly 1 million acres (924,000).
  • Areas experiencing the most significant activity are on the San Juan and Rio Grande National Forests in southern Colorado.
  • Spruce beetles typically attack spruce trees downed by high winds. Once the populations of spruce beetles build up in the fallen trees, the stressed trees surrounding them offer little resistance to attack.
  • Similar to mountain pine beetle, the increase in spruce beetle activity is due to factors that increase tree stress, including densely stocked stands, ongoing drought conditions and warmer winters.

Aerial survey maps and related materials are available on the USFS Region 2 website.

Spruce regeneration, more than 40 years old, near the upper Rio Grande River.Learn More About Common Forest Insects and Diseases

2012 Forest Health Report

Aerial Survey Maps from the 2012 Report

CSFS Insect & Disease Quarterly Reports