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 district office to conduct a homesite assessment of the trees on your property.

2013 Forest Health Aerial Survey Results

Click on the 2013 Insect and Disease Activity map to view a full-size version (154 KB PDF).

On Jan. 30, 2014, the U.S. Forest Service and Colorado State Forest Service released the results of the annual aerial insect and disease survey in Colorado.

Each summer the agencies work together to aerially monitor insect and disease-caused tree mortality or damage across Colorado forestland.

The survey indicates that the spread of the mountain pine beetle epidemic has slowed dramatically, while the spruce beetle outbreak continues to expand.

Click on the 2013 Insect and Disease Progression 1996-2013 map to view a full-size version (180 KB PDF).

Mountain Pine Beetle

  • The mountain pine beetle epidemic slowed again in 2013, with the lowest acreage of active infestation observed in 15 years.
  • Statewide, mountain pine beetle was active on 97,000 acres in 2013.
  • This brings the total infestation to 3.4 million acres in Colorado since the first signs of the outbreak in 1996.

Spruce Beetle

  • The spruce beetle outbreak was active on 398,000 acres across the state, expanding by 216,000 new acres in 2013, compared to 183,000 new acres in 2012.
  • The total area affected by this beetle since 1996 has reached more than 1.1 million acres.


  • Conversely, aspen forest conditions in the state have continued to improve.
  • The aerial survey indicates that although there is continued mortality following drought in the early 2000s, the decline has slowed, with only 1,200 acres impacted in 2013.

For more highlights on the 2013 aerial detection survey, visit the US Forest Service Rocky Mountain Region website.

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

2013 Forest Health Report

2013 Insect & Disease Maps

2013 Insect & Disease Update - A Supplement to the 2013 Forest Health Report