What’s Killing Trees Around Park City?
A closer look at five threats to tree health affecting the Wasatch Back.
What’s bugging your trees?
The 5 Biggest Pests & Diseases Threatening Summit County
Do trees cry when they’re sick? Do they call out? Well, yes, kind of. If you know what you’re looking for... something you may already well know if you too are surrounded by trees at home. By the time a canopy gets sparse, evergreens turn red, or a trunk is weeping sap, whatever's causing it usually has a head start. So this month we’re walking through the five biggest things we see happening in the local tree world, here in Summit County.
Jump to a tree threat
Five threats. Five patterns. The earlier you recognize what a tree is showing you, the more options you may have.
Douglas-fir beetle
This is one's hitting closest to home. In May 2025, a localized outbreak was reported in Summit Park. An estimated 50 - 60 large, mature Douglas-firs were dead or in severe decline on private lots near Matterhorn Drive and in a small piece of adjoining open space. The Summit Park HOA, Summit County, and the Utah Division of Forestry, Fire & State Lands began working together on containment, but there was no indication the infestation would remain inside that pocket.
Douglas-fir beetles are most likely to build up in trees already stressed by drought, overcrowding, fire injury, or root damage. And warm, dry conditions can add to that stress.
Warning signs
Look for reddish boring dust caught in bark crevices, pitch streaming or small pitch tubes on the trunk, and a crown that fades from green to yellow or reddish brown. If you have Douglas-fir in or near Summit Park, check now rather than waiting for the whole crown to change color.
Mountain pine beetle
This is the outbreak many longtime residents remember. By 2010, mountain pine beetle had affected more than 407,000 acres in the Uinta-Wasatch-Cache National Forest, with Summit County’s lodgepole pine stands among the hardest hit. That number is a historical snapshot but the deadwood and changes in stand structure are still part of the forest we manage today.
Warning signs
Watch for cream, pink, or amber pitch tubes; reddish-brown boring dust tucked into bark crevices or around the base; and needles that fade from green to yellow and then rust-red. Woodpecker activity can be another clue.
Spruce beetle
Spruce beetle gets less attention around Park City, but it has reshaped high-elevation forests across the Intermountain West. In Utah, its main host is Engelmann spruce. Outbreaks can expand after drought, windthrow, or other disturbances leave stressed trees and fresh downed spruce available for breeding. The result is often visible for years: red crowns first, then broad gray stands of dead spruce.
One thing to pay attention to when you are identifying a problem: spruce beetle does not explain mortality in lodgepole pine. Similar-looking damage on lodgepole calls for a different diagnosis, most often mountain pine beetle.
Warning signs
Look for fine reddish-brown boring dust in bark crevices and at the tree’s base, small pitch tubes or resin, and fading needles on Engelmann spruce. Needles may drop before the crown develops the dramatic red color people expect.
Balsam woolly adelgid (BWA)
This one is newer, easy to miss, and confirmed in Summit County! Balsam woolly adelgid (BWA) is a tiny, non-native, sap-feeding insect first observed killing subalpine fir in northern Utah in 2017. It has since been confirmed in ten Utah counties, including Summit and Wasatch.
A 2024 University of Utah study estimated that 41% of the subalpine-fir biomass in its northern Utah study area was climatically exposed to some level of BWA damage. Under a moderate warming projection, that share rises to 79% by 2100. Unlike a bark beetle, BWA settles on the bark and feeds through a slender stylet. Mortality usually takes two to ten years, although a heavy infestation can kill a tree in two to three.
Warning signs
Look for tiny white woolly masses on the lower trunk, “gouting” or swollen branch nodes, stunted growth, yellowing or bronzing needles, and a crown that curls, thins, or loses its leader.
Cytospora canker (aspen)
If you have aspen around the house (and plenty of Wasatch Back homes do!) Cytospora belongs on the short list when branches begin to die back. USU Extension calls it one of the most common diseases of ornamental aspen twigs and stems! The fungus enters through wounds and is most successful in trees already weakened by drought, heat, poor drainage, root injury, or other stress.
That helps explain why a lawn-grown aspen can struggle even when wild aspen nearby look fine. A single ornamental tree is living in a very different root environment from a connected aspen clone. The practical goal is to reduce stress and catch damaged branches early; fungicides are not effective against Cytospora canker.
Warning signs
Look for sunken or discolored bark, orange to brown staining or ooze, small orange spore tendrils in wet weather, and progressive twig or branch dieback. A canker can girdle a branch by killing the cambium around it.
What to actually do with this
You of course don't need to inspect every tree with a magnifying glass. Just start with changes you can see: fresh boring dust, new pitch, white wool on fir bark, swelling at branch nodes, oozing or sunken bark, or needles changing color out of season.
Remember stress plays a huge part, too: drought, crowding, root injury, poor soil, and heat can leave a tree with fewer resources to contain insects or infection. Reducing avoidable stress improves the odds but doesn't guarantee, especially with an invasive pest such as balsam woolly adelgid.
Identification comes before treatment. Several of these problems produce similar symptoms, and by the time an entire crown turns red, the useful management window may have narrowed. If something looks off, document what you see and have the tree assessed before cutting, spraying, or moving infested wood.
Notice something on your trees that doesn't look right?
Reach out, and we’ll take a lookSources & photo licenses
- TownLift, “Aggressive outbreak of Douglas-fir beetle detected in Summit Park” (May 2025) the reported Summit Park location, scale, symptoms, and multi-agency response.
- Utah State University Extension, Bark Beetles: Identification and Control (PDF)—Utah host trees, biology, signs, prevention, and management for Douglas-fir, mountain pine, and spruce beetles.
- The Park Record, “Bark beetles killing the forest” (June 2010)—the historical 407,000-acre mountain pine beetle figure for the Uinta-Wasatch-Cache National Forest.
- Utah State University Extension, “Balsam Woolly Adelgid” (revised April 2023)—Utah distribution, symptoms, mortality timing, monitoring, and management.
- University of Utah, “Meet the new insect killing Utah’s fir trees” (May 2024)—the 41% current and 79% projected climatic-exposure estimates for subalpine-fir biomass in the study area.
- Utah State University Extension, “Important Pests of Ornamental Aspen”—Cytospora infection, symptoms, stress relationship, and management guidance for ornamental aspen.
- Photographs: Douglas-fir beetle damage (USDA Forest Service, public domain); mountain pine beetle pitch-outs (Padraic Ryan, CC BY-SA 3.0); spruce beetle damage (John Sowell, CC BY-SA 4.0); balsam woolly adelgid (Robert L. Anderson/USDA Forest Service/Bugwood.org, CC BY 3.0 US); and Cytospora chrysosperma (P Holroyd, CC BY 4.0). License links are repeated beneath each image.
