Counties most impacted in southwest Colorado in 2023: widespread

Western spruce budworm (Choristoneura occidentalis) is a ubiquitous forest pest in spruce-fir forests in southwest Colorado – and across much of the entire state. Once again, the budworm made the list of top forest health concerns for all five Colorado State Forest Service field offices in this part of the state.

The Montrose Field Office staff reports significant defoliation of Engelmann spruce, subalpine fir and Douglas-fir from the budworm throughout its service area, notably around Telluride and north into the Sneffels Range near Lost Dollar Road.

Out of Durango, CSFS foresters are tracking impacts from the budworm in the high-elevation forests of La Plata, San Juan and Archuleta counties. Over the past decade, it has also caused significant defoliation to Douglas-fir and spruce trees in Gunnison and Saguache counties.

Defoliation from western spruce budworms can weaken trees and make them susceptible to attack from deadly bark beetles. This is occurring in spruce-fir forests in this part of Colorado, with defoliation so bad over multiple years in some forests that the budworm is killing trees outright. The budworm also feeds on and kills young Douglas-fir and Engelmann spruce trees, further spiraling forests into decline.

Residents often overlook this forest pest until their trees are almost dead, so it is important that they know the signs of budworm infestation and contact their local CSFS office for assistance.

Counties most impacted in southwest Colorado in 2023: Dolores, Gunnison, La Plata, Mineral, Rio Grande, Saguache

Ongoing drought and widespread defoliation from western spruce budworms are stressing Douglas-fir trees in southwest Colorado, leading to upticks in activity from the Douglas-fir beetle (Dendroctonus pseudotsugae). Drought and defoliation from the budworm weaken trees, and this bark beetle can subsequently kill them.

Outbreaks of Douglas-fir beetles have grown in low-elevation forests in central and southwestern Colorado over recent years, with the beetles feasting on stressed trees in over-dense stands. This is concerning because dry, mixed-conifer forests with Douglas-fir trees make up a large component of the wildland-urban interface for many communities, increasing wildfire risks to homes and businesses.

The Colorado State Forest Service has many projects across southwest Colorado to remove these wildfire fuels, including one on Poncha Pass on the border between Chaffee and Saguache counties. CSFS foresters and partners removed trees infested or killed by western spruce budworm and Douglas-fir beetles. Removing these dead and dying trees improved forest health and lowered wildfire risk to homes, utility lines, watersheds and U.S. Highway 285 that serves as a primary evacuation route for residents in the area.

Counties most impacted in southwest Colorado in 2023: Gunnison, Mesa, Montrose

New pockets of trees killed by mountain pine beetle (Dendroctonus ponderosae) continue to expand in north Gunnison County forests. The area experienced below-average snowpack for the winters of 2018-19 through 2021-22. In 2023, snowpack returned to above average, though trees will likely remain drought-stressed until multiple years of average to above-average precipitation returns.

The prolonged drought stresses pines, which rely on moisture from melting winter snowpack for early summer growth. In the coming months, poor tree health will likely spur even more beetle activity within lodgepole pine stands.

Beetle activity is most prevalent in the Taylor River drainage, Ohio Creek, East River and near Crested Butte. Colorado State Forest Service foresters are seeing new pockets of beetle-killed trees throughout Gunnison County, often in areas inaccessible for forest management.

Gunnison County is not alone when it comes to this beetle. CSFS foresters in other areas of southwest Colorado have also noticed mountain pine beetle activity in forests.

Counties most impacted in southwest Colorado in 2023: Dolores, La Plata, Montrose, San Miguel

Colorado State Forest Service foresters and entomologists continue to monitor an outbreak of roundheaded pine beetle (Dendroctonus adjunctus) and associated native pine bark beetles in the Glade area of the San Juan National Forest northwest of Dolores. Despite having fewer suitable trees to attack, it continues to intensify and expand its footprint in this area.

In 2021, tree mortality in San Miguel County increased from the native pine bark beetle complex. Last year, significant areas were detected in Montrose County, indicating these bark beetles are expanding through the vast pine forests in this region.

The roundheaded pine beetle is a native bark beetle that has thrived in southwest Colorado during recent years due to ongoing drought conditions that have weakened trees. It often works with other bark beetles, including the mountain pine beetle, to injure and kill ponderosa pines.

With only one generation flying yearly, these beetles attack various tree sizes and ages. They often attack later in the year, in October and November, leaving drought-stressed trees under attack from beetles for much of their growing season.

Counties most impacted in southwest Colorado in 2023: Chaffee, Costilla, Gunnison, Hinsdale, La Plata, Mesa, San Juan

Spruce beetle (Dendroctonus rufipennis) remains active in forests in southwest Colorado despite a statewide decline. This bark beetle has depleted susceptible Engelmann spruce in some areas and is attacking lodgepole pine. It prefers large-diameter trees but attacks and kills trees as small as 4 inches in diameter.

Colorado State Forest Service foresters in the Alamosa office have noticed impacts from the spruce beetle throughout the Culebra Range in Costilla County south to the New Mexico border. In Chaffee County, spruce beetle continues to move north of the Chalk Creek drainage to Mount Columbia, northwest of Buena Vista. Chaffee County was the most impacted county statewide in 2023.

Spruce beetle-caused mortality in forests north of Durango and south of Silverton in the Needle and San Juan mountains within Hinsdale, La Plata and San Juan counties is expanding to previously uninfested areas, indicating the beetle is still on the move and will likely cause damage in the coming year.

CSFS foresters manage spruce beetles by removing susceptible and affected trees before an outbreak. The CSFS has continued a large-scale salvage effort on the Alpine Plateau between Gunnison and Montrose to curb a potential spruce beetle outbreak there.

A way to manage for spruce beetle on smaller acreage is by placing pheromone packets on trees. These packets release a chemical that tricks beetles into thinking an otherwise healthy tree is already infested with beetles. These treatments will be available through the CSFS in early 2024. Contact your local CSFS office for more information.