Western spruce budworm is the most widely distributed forest defoliator in western North America.

Budworms have a one-year life cycle and are actually a small moth at full maturity. Here in the West, there can be severe infestations in healthy Douglas-fir, white fir and spruce.

Symptoms of Infestation

Evidence of western spruce budworm can be observed year-round. Dead branches or sparse foliage may indicate feeding during previous years. Budworms have the potential to consume all new growth on the host tree. During outbreaks of three or more successive years, trees may die. Budworms create ideal conditions for other insect and disease invasions.

Management Options

  1. Budworm populations can be substantially reduced with chemical insecticides. Large forested areas can be aerially sprayed for short-term protection, and individual trees can be sprayed using ground equipment. (Always carefully read and follow all label instructions before applying insecticides.)
  2. Promoting tree vigor through silvicultural methods such as thinning or promoting mixed-tree stands will help reduce the risks of an infestation.
  3. Generally, budworm populations are kept under control by a combination of predators, parasites, climatic conditions or insufficient food supplies.

Learn More About Western Spruce Budworm

2018 Western Spruce Budworm Activity

County2017
Acres Affected
2018
Acres Affected
Alamosa1,7001,600
Archuleta4,20020
Chaffee7,7007,000
Conejos4,6002,600
Costilla6,0005,600
Custer11,0005,900
Delta5803
Dolores5,00013,000
Eagle1600
El Paso7201,300
Fremont11,00012,000
Garfield3,8004
Grand910200
Gunnison42,00011,000
Hinsdale560720
Huerfano13,0001,200
Jefferson540150
La Plata3,70040
Larimer3,900430
Las Animas11,000710
Mesa780210
Mineral2,600830
Montezuma3,9005,100
Montrose2,300410
Ouray3,2002,100
Park12,00014,000
Pitkin1,200340
Pueblo7800
Rio Blanco11,000430
Rio Grande1,900220
Routt1,7001,000
Saguache75,00030,000
San Juan12090
San Miguel3,90011,000
Teller1,3002,200