Every tree species has its cadre of insects and diseases. In most cases, the insect or disease is very particular about what it attacks.

Tree-Related Insects & Diseases

A healthy tree's defense against pine beetle
A healthy tree’s defense against pine beetle

Not every insect found on a tree is there to harm the tree. Some insects are beneficial because their job is to prey on the insects that are chewing on or burrowing into the tree. Before applying any insecticide, identify what insect is causing the damage, and if the damage is more superficial than harmful, consider not spraying.

Every tree species has its cadre of insects and diseases. In most cases, the insect or disease is very particular about what it attacks. A Douglas fir beetle is not interested in a spruce tree. The dwarf mistletoe found in pine trees cannot infect junipers. So, diversity in tree species and age makes the forest more resilient to large outbreaks or epidemics.

Tree-killing Insects

Many insects leave unsightly messes, but they will not kill a mature tree in a year. The family of bark beetles in the Dendroctonus genus do kill trees within one life cycle. Chaffee and Lake counties have both experienced mountain pine beetle (Dendroctonus ponderosae). In Chaffee County, the beetles prefer ponderosa pine. In Lake County, the beetles attack lodgepole pine. The spruce beetle and Douglas fir beetle are also in the Dendroctonus genus and kill their namesakes.

Other native beetles attack and kill trees after something else has sufficiently weakened the tree. That other “thing” can be drought, lightning strike, construction damage, chronic attack by “minor” insects, disease or a combination of the above. Examples include Ips confusus in pinon pine and western balsam bark beetle in subalpine fir.

In the community setting, emerald ash borer, a non-native species, is a potential threat to ash trees. The borer has NOT been detected in Chaffee County, but it could be transported into the county via ash firewood. Symptoms are initially inconspicuous which allows the population to build and spread undetected. If you have a sickly ash tree, please contact our office or a certified arborist to examine the tree.

Western Spruce Budworm

The spruce budworm is sometimes confused with the spruce beetle because of similar names. Spruce budworms prefer to feed on new needles of Douglas-fir and white fir trees in south-central Colorado, while spruce beetles burrow under the bark of primarily Engelmann spruce trees, generally above 9,000 feet.

Last summer, Methodist Mountain and the Collegiate Peaks sported a brown tinge where Douglas-fir grow. Enough Douglas-fir branch tips were killed by western spruce budworm in early summer to create what looked like a bathtub ring on the mountainsides. Western spruce budworms have been impacting Saguache County for several years and the population is rising in Chaffee and Fremont counties.

In 2016, more than 200,000 acres statewide were impacted by western spruce budworm, and Chaffee, Fremont and Saguache counties had approximately 50,000 combined acres impacted.

The CSFS Salida District hosted a free presentation by Dr. Dan West, CSFS entomologist, titled “The Budworms are Back!” on April 27, 2017 in Poncha Springs. The purpose of the presentation was to give landowners and forest users a better understanding of western spruce budworm.

View a summary of the presentation (PDF) that includes the life cycle of the spruce budworm, how the budworm affects tree health, options for control, and other insects associated with Douglas-fir. Also, check out a pesticide comparison chart (PDF) from the National Pesticide Information Center. Hard copies of these documents are available at the district office.

Dwarf Mistletoe

Dwarf mistletoe in Lake and Chaffee counties can be found on ponderosa pine, lodgepole pine and Douglas fir.
Dwarf mistletoe in Lake and Chaffee counties can be found on ponderosa pine, lodgepole pine and Douglas fir.

Dwarf mistletoe is a parasitic plant that slowly kills a tree. The amount of time it takes to kill a tree depends on how young the tree was when it first became infected. Although dwarf mistletoe can take a long time to kill a large tree, it has an interesting method of spreading where sticky seeds shoot out of small capsules. A heavily infected tree has deformed branches, grows slowly and produces few viable tree seeds. Dwarf mistletoe is species specific. In Lake and Chaffee counties, dwarf mistletoe can be found on ponderosa pine, lodgepole pine and Douglas fir.

Our foresters can sometimes troubleshoot problems from the office; otherwise they are available by appointment to assess an insect or disease problem on your favorite tree, on your property or within a subdivision.

Fact sheets addressing specific insects and disease are available in our office and in the Publications section of our CSFS website.