Trees and shrubs

Tree, shrub and fruit tree pests

Timing decides most tree-pest problems: bagworms are easiest to control as young larvae, ash trees can only be protected while they're still healthy, and codling moth damage is prevented early in the season, not at harvest.[11][12][13]

The short answer

  • Bagworms: pick off and destroy bags in fall through spring, cutting the silk band so it doesn't girdle the branch; spray Bt on young larvae at the end of June.[11]
  • Emerald ash borer: healthy or newly infested ash can be protected with systemic insecticides, but treatment must be repeated regularly; trees with less than half their canopy left are better removed and replaced.[12]
  • Codling moth: pick up dropped fruit, remove infested fruit, and bag young apples and pears 4 to 6 weeks after bloom.[13]
  • Pheromone traps mostly tell you when to act; they aren't a reliable way to reduce damage on their own.[13][22]

Bagworms

Bagworms build spindle-shaped silk bags, 1-1/2 to 2-1/2 inches long, covered with bits of foliage. They prefer arborvitae and red cedar but attack many conifers and broadleaf trees, from New England to Nebraska and south through Texas.[11]

  • Females can't fly, so populations build up quickly on favored hosts. Heavy feeding can kill buds and branches, and severe defoliation can kill arborvitae, cedar or juniper the following season.[11]
  • Each overwintering bag can hold 300 to 1,000 eggs, which hatch in late May or early June; tiny larvae balloon on silk to nearby plants.[11]
  • Hand-pick bags in late fall, when they turn brown and are easy to see, and cut the silk band attaching them, which can girdle the branch years later.[11]
  • Bt works only against young larvae; apply it at the end of June after eggs have hatched and ballooning is over. With any spray, cover foliage thoroughly, because larvae are protected inside the bag.[11]

Emerald ash borer

Emerald ash borer is an invasive beetle that kills true ash trees (Fraxinus). Its larvae tunnel just under the bark, cutting off water and nutrients. Mountain ash isn't a true ash and isn't attacked.[12]

  • Early signs: dieback in the top third of the canopy, more woodpecker activity, and sprouts on the lower trunk. Adults leave D-shaped exit holes; vertical bark splits appear as the tree declines.[12]
  • Adults are metallic green, about 1/2 inch long and 1/8 inch wide.[12]
  • White and green ash usually survive 7 to 10 years after infestation, but can die in 1 to 2 years when beetle numbers are high or the tree is already stressed.[12]
  • Systemic insecticide treatment is currently the only way to protect a tree, and it must be repeated for the foreseeable future. Treat healthy trees you value; remove trees that are badly damaged, defective or recently planted, and replace with a mix of species.[12]

Asian longhorned beetle (report it)

  • A shiny black beetle about the size of an almond, with white spots and black-and-white antennae longer than its body. It attacks and kills maples and other hardwoods.[2]
  • Signs: round exit holes about the size of a dime or smaller, oval or round egg-site wounds chewed in the bark, sawdust-like frass, and limbs falling from healthy-looking trees.[2]
  • USDA is working to eliminate infestations in central Long Island, NY; Worcester County, MA; Clermont County, OH; and Charleston County, SC. Report a suspect beetle or damage to the ALB hotline, 1-866-702-9938, with a photo, and freeze the beetle in a container if you can.[2]

Peachtree borer, twig girdlers and cottonwood borer

  • Peachtree borer larvae tunnel in the lower trunk of peaches, cherries, plums and ornamental Prunus; the first sign is a mass of gum mixed with sawdust and frass from about 3 inches below to 12 inches above the soil. Adults are wasp-like clearwing moths.[3]
  • Stressed, transplanted or mower-wounded trees are attacked more. Don't pile mulch against Prunus trunks, avoid bark wounds, and remove severely infested trees.[3]
  • Twig girdlers are longhorned beetles; from late August through October females chew a clean V-shaped groove around a twig and lay eggs above it, so the girdled twig tips drop. Pecan twig girdlers also attack elm, hickory, oak, persimmon and citrus.[4]
  • Cottonwood borers are large, 1-1/4-inch black-and-cream longhorned beetles whose larvae tunnel around the crown and buttress roots of cottonwoods, poplars and willows.[5]

Bark beetles

  • Adults are small, dark, cylindrical beetles about the size of a grain of rice; look for many tiny holes, boring dust, holes oozing sap and a declining crown, and galleries under the bark.[14]
  • Native bark beetles mostly attack trees already stressed by drought, disease or injury, though some invasive species kill healthy trees. Healthy trees fight off light attacks by pushing out sap.[14]
  • Water trees properly, thin dense stands, and avoid compacting soil or injuring roots and trunks. Insecticides won't save a heavily infested tree; remove it promptly and chip the wood, or solarize small piles under thick clear plastic for several months.[14]

Pine sawflies

  • Sawfly larvae look like caterpillars but have more than five pairs of fleshy legs on the abdomen; they feed in groups and can strip needles quickly.[21]
  • Bt, which works on moth and butterfly caterpillars, doesn't work on sawflies. Handpick, shake off or prune out small colonies; insecticidal soap works if it hits the larvae directly.[21]

Psyllids, lace bugs and woolly aphids

  • Psyllids are aphidlike insects, 1/10 to 1/5 inch, that jump when disturbed and leave sticky honeydew, sooty mold, white wax or distorted leaves; most plants tolerate low to moderate numbers.[15]
  • Conserve the lady beetles, pirate bugs and parasitic wasps that attack psyllids, fertilize less to avoid succulent growth, and use soaps or oils only for heavy infestations.[15]
  • Lace bugs, about 1/8 inch with lacelike wings, leave pale stippling and black specks under leaves; the damage is mostly cosmetic.[16]
  • Woolly aphids hide under white, waxy fluff; brush the wax away to see the insects, since adelgids, mealybugs, psyllids and woolly whiteflies look similar. Woolly apple aphid causes warty galls on apple and pyracantha bark and roots.[17]

Hemlock woolly adelgid

  • The giveaway is white, cottony wax masses at the base of hemlock needles; tiny black females overwinter beneath them. Severe infestations cause needle drop, dieback and can kill eastern hemlocks.[6]
  • Late September through October is the best time to treat with a labeled insecticide, targeting overwintering females; commercial applicators can soil-inject systemic insecticides around large trees, best in early spring with good soil moisture.[6]

Box tree moth

  • An invasive moth whose caterpillars feed only on boxwood. First found in Toronto in 2018 and in New York in 2021, it has since been confirmed in Michigan, Ohio, Massachusetts and Pennsylvania.[7]
  • Caterpillars are green and yellow with white, yellow and black stripes and black spots; young ones leave leaves looking peeled, older ones eat all but the midrib and web leaves together. Extensive feeding can kill whole plantings.[7]
  • Adults are mostly white with a brown border; 5 to 10 percent are entirely brown except for white commas on the forewings.[7]

Browntail moth (Maine and New England)

  • The caterpillars' microscopic toxic hairs break off and float in the air or settle on surfaces, causing a rash like poison ivy and sometimes trouble breathing that can last hours to weeks.[8]
  • In Maine it occurs along the coast and up to 60 miles inland. Caterpillars leave their winter webs to feed in mid-April, so clip and destroy webs between October and March, wearing long sleeves, goggles, a dust mask and disposable coveralls.[8]

Black vine weevil

  • Adults are flightless, slate-gray to black weevils about 3/8 to 1/2 inch long that notch the edges of rhododendron, yew, euonymus and Japanese holly leaves at night; the notching seldom hurts the plant.[9]
  • The white, C-shaped larvae feed on roots and can girdle them, killing plants, especially ones moved from containers to landscapes. Boards or burlap laid on the mulch in early May reveal when adults appear; treat foliage three weeks after the first adult, or use beneficial nematodes against larvae in containers.[9]

Spruce spider mite

  • A cool-season mite that speckles and bronzes the older inner needles of spruce, arborvitae, juniper, hemlock and pine; dwarf Alberta spruce is a favorite.[10]
  • Strike a branch over white paper: ten or more dark mites at each of several spots justifies a miticide, best in early to mid-May and again in early September. Some insecticides can make mite outbreaks worse.[10]

Oak galls

  • Galls are abnormal plant growths triggered by chemicals from insects such as tiny gall wasps. Most leaf galls on oak cause little or no harm, but woody twig galls such as horned oak gall and gouty oak gall can injure or even kill heavily infested trees.[1]
  • The horned oak gall has small horns around it, each the exit point of one adult wasp; it attacks pin, scrub, black, blackjack and water oaks.[1]
  • Once a gall starts it can't be stopped. Rake and destroy fallen infested leaves, and prune woody galls while they're small; insecticides are seldom useful.[1]

Elm leaf beetle

Adults are 1/4-inch olive-green beetles with black stripes that chew shothole patterns through elm leaves, while larvae skeletonize leaf surfaces; repeated defoliation weakens trees. European elms suffer most; most Chinese elm cultivars and zelkova are rarely fed on.[18]

Codling moth in apples and pears

  • Sanitation comes first: every week or two, starting 6 to 8 weeks after bloom, remove fruit with frass-filled holes, and pick up dropped fruit promptly, especially in May and June.[13]
  • Bagging is the only nonchemical method effective enough to use alone. When fruit is 1/2 to 1 inch across, thin to one per cluster, slip each fruit through a 2-inch slit in a paper lunch bag, and staple it shut. Nylon bags don't work.[13]
  • Prune trees to a height where you can reach the canopy, which makes all of this easier.[13]
  • Peach twig borer larvae, chocolate brown with pale bands and a black head, are a pest of almonds and stone fruits. If damage was intolerable before, Bt applied at bloom (just after first blooms open and again 7 to 10 days later) or spinosad at petal fall, late in the day after bees stop flying, works best.[20]
  • Walnut husk fly mostly stains walnut shells; it generally doesn't affect the nutmeats, so most home orchardists can ignore it.[19]

How pheromone traps really work

Most pheromone traps use a lure that mimics a female moth's scent to attract males to a sticky surface. Their main use is monitoring: codling moth traps hung high in the canopy in March, checked every few days, show when moths are flying so you can time treatments.[13]

  • Hanging traps in a tree to trap out codling moths isn't a reliable way to reduce damage; if it helps at all, it's on isolated trees with several traps.[13]
  • Japanese beetle traps can make damage worse: University of Kentucky research found they attract many more beetles than they catch.[22]

Sources

  1. Penn State Extension, “Galls on Oak (updated June 24, 2026).” extension.psu.edu/galls-on-oak (accessed 2026-10-06)
  2. USDA Animal and Plant Health Inspection Service, “Asian Longhorned Beetle (last modified September 17, 2026).” www.aphis.usda.gov/plant-pests-diseases/alb (accessed 2026-10-06)
  3. Penn State Extension, “Peachtree Borer (updated April 10, 2026).” extension.psu.edu/peachtree-borer (accessed 2026-10-06)
  4. Texas A&M AgriLife Extension, “Twig Girdler (Field Guide to Common Texas Insects).” texasinsects.tamu.edu/twig-girdler/ (accessed 2026-10-06)
  5. Texas A&M AgriLife Extension, “Cottonwood Borer (Field Guide to Common Texas Insects).” texasinsects.tamu.edu/cottonwood-borer/ (accessed 2026-10-06)
  6. Penn State Extension, “Hemlock Woolly Adelgid (updated June 24, 2026).” extension.psu.edu/hemlock-woolly-adelgid (accessed 2026-10-06)
  7. Penn State Extension, “Box Tree Moth (updated January 19, 2026).” extension.psu.edu/box-tree-moth (accessed 2026-10-06)
  8. Maine Forest Service, “Browntail Moth, Euproctis chrysorrhoea (Forest Health & Monitoring).” www.maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_info.htm (accessed 2026-10-06)
  9. Penn State Extension, “Black Vine Weevil (updated June 24, 2026).” extension.psu.edu/black-vine-weevil (accessed 2026-10-06)
  10. Penn State Extension, “Spruce Spider Mite (updated June 24, 2026).” extension.psu.edu/spruce-spider-mite (accessed 2026-10-06)
  11. Ohio State University Extension, “HYG-2149: Bagworm and Its Control.” ohioline.osu.edu/factsheet/HYG-2149-10 (accessed 2026-10-06)
  12. University of Kentucky Entomology, “ENTFACT-453: Emerald Ash Borer (EAB) FAQs for Kentuckians.” entomology.mgcafe.uky.edu/ef453 (accessed 2026-10-06)
  13. University of California Statewide IPM Program, “Codling Moth (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/codling-moth/ (accessed 2026-10-06)
  14. University of California Statewide IPM Program, “Bark Beetles (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/bark-beetles/ (accessed 2026-10-06)
  15. University of California Statewide IPM Program, “Psyllids (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/psyllids/ (accessed 2026-10-06)
  16. University of California Statewide IPM Program, “Lace Bugs (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/lace-bugs/ (accessed 2026-10-06)
  17. University of California Statewide IPM Program, “Woolly Aphids (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/woolly-aphids/ (accessed 2026-10-06)
  18. University of California Statewide IPM Program, “Elm Leaf Beetle (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/elm-leaf-beetle/ (accessed 2026-10-06)
  19. University of California Statewide IPM Program, “Walnut Husk Fly (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/walnut-husk-fly/ (accessed 2026-10-06)
  20. University of California Statewide IPM Program, “Peach Twig Borer (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/peach-twig-borer/ (accessed 2026-10-06)
  21. University of Kentucky Entomology, “ENTFACT-410: Pine Sawflies.” entomology.mgcafe.uky.edu/ef410 (accessed 2026-10-06)
  22. University of Kentucky Entomology, “ENTFACT-451: Japanese Beetles in the Urban Landscape (revised March 2026).” entomology.mgcafe.uky.edu/ef451 (accessed 2026-10-06)

Updated 2026-10-06. Built from sourced records. Spot an error? Tell us.