Common Tree Pests in Utah

Common tree pests in Utah include Ips and other bark beetles, lilac-ash borer, flatheaded borers, aphids, scale insects, spider mites, cankerworms, and western tent caterpillars. The pests affecting Utah trees create three main types of injury: wood-boring damage, sap-feeding damage, and foliage loss from defoliating caterpillars.

Tree insect identification in Utah is most reliable when the tree species, damaged plant part, visible insect sign, and time of year all match. Drought stress is especially important with bark beetles and borers, since weakened trees have fewer defenses against insects feeding beneath the bark.

Key Takeaways

• Ips beetles can cause top-down fading in stressed pines and spruces, often with pitch, boring dust, and Y- or H-shaped galleries.
• Lilac-ash borer activity is concentrated in spring and early summer; many flatheaded borers peak around June and July.
• Honeydew points toward aphids or soft scales. Armored scales feed differently and do not produce honeydew.
• Spruce spider mites favor cool spring and fall weather, while two-spotted and McDaniel mites favor hot, dry conditions.
• Cankerworms and western tent caterpillars are mainly spring defoliators, although their feeding patterns and life cycles differ.

The Most Common Utah Tree Pests and How to Identify Them

1. Ips and Bark Beetles

Ips and related bark beetles are small wood-boring insects.

• Trees Commonly Affected: Pines, spruces, and pinyons. Spruce Ips commonly attacks blue and Engelmann spruce, while other Ips species attack ponderosa, lodgepole, Jeffrey, and pinyon pines. Drought-stressed trees are especially vulnerable.
• How to Identify Them: Needles fade from green to yellow, reddish brown, or brown, often from the upper crown downward. Look for pitch tubes, reddish or sawdust-like frass, small emergence holes, and galleries beneath the bark. Ips galleries may form Y- or H-shaped patterns. Adults are about 1/8–3/8 inch long.
• When They're Most Active in Utah: Flights are strongest in spring and may rise again in fall. Some Ips begin emerging above about 50°F. One generation can take 6–8 weeks, allowing up to 5 generations per season under favorable conditions.
• Damage They Cause: Adults and larvae feed in conductive tissue beneath the bark, disrupting water and nutrient movement. Heavy attacks can move downward through a tree within months and may kill it within one growing season.

2. Lilac-Ash Borer

Lilac-ash borer is a clearwing moth whose larvae tunnel into trunks and larger branches.

• Trees Commonly Affected: Ash is the main landscape host; lilac and privet are also attacked. Stressed ash trees are more vulnerable.
• How to Identify Them: Adults are 1–1½ inches long, black and yellow, and resemble paper wasps. Larvae are pinkish-white with brown heads and grow to about 1 inch. Round exit holes, sawdust-like frass, loose bark, protruding empty pupal skins, and dying branches are key signs.
• When They're Most Active in Utah: Adults may emerge as early as late March, although early May is more common, and activity usually continues for about six weeks. Broader flight activity can extend from late April through late July. Utah has one generation per year.
• Damage They Cause: Larvae tunnel through cambium and sapwood. A female can lay about 400 eggs, which hatch in roughly 14 days.

3. Flatheaded and Bronze Birch Borers

Flatheaded borers are wood-boring beetles that often attack stressed deciduous trees, with the bronze birch borer especially important on birch.

• Trees Commonly Affected: Bronze birch borer mainly attacks birch, especially paper birch. Paper, silver, and gray birch are more susceptible, while river birch and several other birches have greater resistance.
• How to Identify Them: Look for D-shaped exit holes, winding galleries beneath the bark, raised or swollen ridges over tunnels, and dieback beginning in small upper-canopy branches.
• When They're Most Active in Utah: Adults occur from late May through August, with activity usually peaking in July.
• Damage They Cause: Larvae feed in phloem and etch into sapwood, reducing water and nutrient movement. Continued injury can cause top-down canopy dieback and eventual tree death.

4. Aphids

Aphids are tiny sap-feeding insects most often recognized by distorted leaves, sticky residue, and colonies on new growth.

• Trees Commonly Affected: Utah has more than 500 aphid species. Hosts include maple, ash, apple, crabapple, cherry, elm, beech, cottonwood, poplar, and many other landscape trees.
• How to Identify Them: Most aphids are under 1/8 inch and may be green, yellow, red, purple, or black. Curled or cupped leaves, colonies on tender growth, sticky honeydew, and black sooty mold are common signs.
• When They're Most Active in Utah: New foliage expands in spring.
• Damage They Cause: Sap feeding can distort developing leaves and shoots and reduce vigor when populations are high. Many infestations create obvious leaf distortion and honeydew without serious long-term tree decline.

5. Scale Insects

Scale insects are sap-feeding pests that often look like fixed bumps, shells, or cottony growths on bark and foliage.

• Trees Commonly Affected: Soft scales occur on elm, linden, maple, oak, willow, juniper, yew, and other woody plants. Oystershell scale has more than 130 recorded hosts and commonly affects ash, aspen, cottonwood, lilac, maple, and willow in Utah.
• How to Identify Them: Soft scales are rounded or cottony and produce honeydew. Armored scales, such as oystershell scale, have hard protective covers and do not produce honeydew. Heavy populations can make bark appear rough, crusted, or cracked.
• When They're Most Active in Utah: The mobile crawler stage appears mainly from late spring into summer. Oystershell scale eggs usually hatch from late May into early June, while Fletcher scale eggs hatch from mid-June through late July.
• Damage They Cause: Feeding can cause yellow foliage, early leaf drop, twig death, and branch decline. Soft-scale females may produce about 200–1,000 eggs, while oystershell scale females produce roughly 40–150.

6. Spider Mites

Spider mite activity varies by species, so cool-season spruce mites and hot-weather mites can appear at different times.

• Trees Commonly Affected: Spruce spider mites favor conifers, especially blue and Alberta spruce. Two-spotted mites attack hundreds of plants, while McDaniel mites commonly occur on fruit and other deciduous trees.
• How to Identify Them: Fine yellow or white stippling, bronzing, browning, premature leaf or needle drop, dusty-looking foliage, and fine webbing are typical. Mites can measure less than 1/60 inch.
• When They're Most Active in Utah: Two-spotted and McDaniel mites favor hot, dry summer weather and may complete a generation in 10–14 days. Spruce spider mites are most active in spring and fall and become largely dormant above roughly 80–90°F.
• Damage They Cause: Mites puncture plant cells and remove their contents, creating stippling that can progress to bronzing and foliage loss. Spruce spider mites complete a generation in 2–3 weeks and may produce up to six generations per year.

7. Cankerworms

Cankerworms are spring-feeding inchworms that can cause severe defoliation during periodic outbreaks.

• Trees Commonly Affected: Apple, ash, maple, boxelder, elm, cherry, linden, honeylocust, and red and white oak.
• How to Identify Them: Young larvae make small, irregular holes between leaf veins. Older larvae leave larger holes, move with a looping “inchworm” motion, and may hang from silk threads.
• When They're Most Active in Utah: Eggs hatch around spring budbreak, typically after 148–290 degree days have accumulated above a 50°F developmental threshold. Larvae then feed for about six weeks, while larger outbreaks tend to occur in 5–7-year cycles. 
• Damage They Cause: Healthy trees often refoliate within 4–6 weeks.

8. Western Tent Caterpillars

Western tent caterpillars are native spring defoliators identified by conspicuous silken tents.

• Trees Commonly Affected: Quaking aspen, cottonwood, chokecherry, crabapple, fruit trees, oak, poplar, serviceberry, mountain mahogany, sumac, wild currant, and wild rose.
• How to Identify Them: Dense silken tents around branches are the clearest sign. Hairy caterpillars can reach about 2 inches long, with feeding concentrated around the webbed area early in development.
• When They're Most Active in Utah: Larvae hatch around spring budbreak and pupate about 1–1½ months later. Adults fly from late July through August, with one generation per year in northern Utah.
• Damage They Cause: Caterpillars can strip foliage from branches or entire trees. Severe damage to established ornamental trees is uncommon, although repeated yearly defoliation can reduce growth and may eventually kill weakened trees.

Utah Tree Pest Activity Calendar

Utah tree pest activity changes considerably through the growing season. So, the timing of the insect activities that damage trees in Utah can help narrow the likely cause.

Protect Your Utah Trees with Professional Tree Care from Stewart's Lawn

Professional tree pest care starts with identifying the insect, host tree, active life stage, and depth of injury. Damage developing beneath bark requires a different professional response from surface-feeding aphids, scales, mites, or caterpillars.

Stewart’s Lawn has served Utah homeowners since 1972. Our on-site evaluation of common insects on Utah trees can assess canopy patterns, bark and exit-hole evidence, insect signs, tree stress, and whether the visible damage is active or older.

If you see new dieback, boring dust, pitch, honeydew, heavy webbing, repeated defoliation, or branch decline, schedule a professional tree health evaluation with Stewart’s Lawn.

FAQs

What are the most common tree pests found in Utah?

The most common tree pests found in Utah include Ips and other bark beetles, lilac-ash borers, flatheaded borers, aphids, scales, spider mites, cankerworms, and western tent caterpillars. The tree species and damage pattern usually provide the fastest first distinction.

How can I tell if bark beetles are attacking my tree?

You can tell if bark beetles are attacking your tree by checking for fading that begins high in the crown, pitch tubes, boring dust, small exit holes, and galleries beneath the bark. Y- or H-shaped galleries strongly support an Ips diagnosis.

Which trees are most likely to get insect damage in Utah?

Trees most likely to get insect damage in Utah include stressed pines, spruces, ash, birch, maple, elm, fruit trees, and other broadleaf ornamentals. Risk is pest-specific. For instance, Ips favors stressed conifers, lilac-ash borer targets ash, and bronze birch borer favors weakened birch.

What time of year are tree pests most active in Utah?

Tree pests are most active in Utah from spring through early fall, although each pest has a narrower activity window. Cankerworms and tent caterpillars feed mainly in spring, lilac-ash borer activity rises from spring into early summer, flatheaded borers peak around June and July, and spruce spider mites are strongest in spring and fall.

Are tree pests more common during drought years?

Tree pests can become more damaging during drought years when water stress weakens tree defenses. Ips attacks are closely associated with stressed conifers, several borers favor weakened deciduous trees, and hot, dry conditions can intensify warm-season spider-mite problems.

Can tree pests spread from one tree to another?

Tree pests can spread from one tree to another through several routes. Adult bark beetles and borers can fly to new hosts, Ips can concentrate attacks through aggregation signals, cankerworm larvae can travel on wind-blown silk, and spider mites can disperse through air movement.