Tree Disease and Insect Guide for Hardwoods

The list below shows common and important tree problems. Pests or conditions that affect many host species are listed only under the most common host(s).

Ash

  • borers, ash yellows

Beech

  • beech bark disease, beech blight aphid

Cherry

  • eastern tent caterpillar, cherry scallop, shell moth, black knot

Dogwood

  • dogwood anthracnose, borers, club gall, powdery mildew

Elm

  • vascular diseases, leaf beetles

Hickories

  • decline, gall phylloxera, fall webworm, twig girdlers/pruners, hickory tussock moth

Locust

  • locust leafminer, locust borer, rimosus heart rot

Maples

  • Verticillium wilt, yellow-bellied sapsucker, whitemarked tussock moth

Oaks

  • defoliators, decline, galls, leaf blister, shoestring root rot, borers, scale insects, anthracnose, oak wilt, periodical cicada, twolined chestnut borer, acorn feeders

Sycamore

  • anthracnose, lace bugs, sycamore tussock moth

Yellow Poplar

  • leaf weevil, Columbian timber beetle, aphids

Hardwoods

Ash

  • Pest or Condition: borers
    Evidence: galleries; exit holes; sap, frass associated with entrance hole.
    Effect: wood product degrade; weakening, mortality of ornamentals.
    Notes: avoid injuries; fell brood trees; process sawlogs promptly.
  • Pest or Condition: ash yellows
    Evidence: basal witches broom, growth decline, thin crown, bark cracks, mortality.
    Effect: pronounced growth reduction, eventual mortality.
    Notes: harvest infected forest trees; fertilize infected yard trees.

Beech

  • Pest or Condition: beech bark disease
    Evidence: red, lemon-shaped fruiting bodies visible with hand lens; tiny, white scale
    infested bark; rough, dead bark patches.
    Effect: gradual decline, invasion by secondary organisms, breakage and mortality.
    Notes: infections by nectria fungi follow scale infestation and kill areas of bark; trees can be girdled or may live many years, but continue to deteriorate; some trees are resistant to the scale.
  • Pest or Condition: beech blight aphid
    Evidence: aphids covered with long, white cottony threads on branches, bark.
    Effect: occasional high populations result in profuse honeydew, sooty mold.
    Notes: common on forest trees; little effect.

Cherry

  • Pest or Condition: eastern tent caterpillar
    Evidence: silk webs in branch crotches; larvae.
    Effect: defoliation in early spring.
    Notes: common on roadside cherry and home fruit trees; natural enemies eventually suppress high populations; shiny, dark, cylindrical egg masses around small twigs can be removed to achieve control..
  • Pest or Condition: cherry scallop shell moth
    Evidence: leaves webbed together on branch ends with larvae inside.
    Effect: defoliation, sometimes complete.
    Notes: usually regulated by natural enemies; mostly on black cherry.
  • Pest or Condition: black knot
    Evidence: rough, black elongate branch galls.
    Effect: progressive branch dieback.
    Notes: prune out and remove infected branches before early spring.

Dogwood

  • Pest or Condition: dogwood anthracnose
    Evidence: tan, purple rimmed leaf spots, brown blotches and margins; starts in lower crown; dead leaves often persist.
    Effect: tree mortality.
    Notes: mostly a problem at altitudes above 1000 feet and in moist conditions; confirmation requires lab culture; prune water sprouts to reduce infection; spot anthracnose, leaf spot very common on dogwoods and not serious .
  • Pest or Condition: borers
    Evidence: withering leaves, twig dieback, sunken bark, basal wounds.
    Effect: dead twigs; decline; sometimes mortality.
    Notes: twig borer larva kills only small stems, can be pruned out; main stem borer
    usually gains entry through wounds, larvae feed on cambium and can girdle tree;
    protect trees against lawnmowers, string trimmers.
  • Pest or Condition: club gall
    Evidence: swellings on small twigs.
    Effect: some tip dieback.
    Notes: very common, caused by a midge (gnat-like fly).
  • Pest or Condition: powdery mildew
    Evidence: bright white to grayish patches or complete covering of leaf surface.
    Effect: distortion, discoloration of developing and developed leaves.
    Notes: weather related; suppression not necessary; don't fertilize while infected.

Elm

  • Pest or Condition: vascular diseases
    Evidence: wilting, yellowing of foliage; sapwood stain.
    Effect: branch dieback, mortality.
    Notes: Dutch elm disease can be prevented and treated through sanitation and
    fungicidal injection; it can be confirmed through culture; no treatment is available for elm yellows.
  • Pest or Condition: leaf beetles
    Evidence: skeletonizing; larvae.
    Effect: heavy defoliation, nuisance from descending larvae.
    Notes: several species; elm leaf and larger elm leaf beetles noticed most in yards.

Hickories

  • Pest or Condition: decline
    Evidence: premature leaf coloration; progressive dieback; attacks of secondary
    organisms.
    Effect: decline over several years, often leading to mortality.
    Notes: episodes have been associated with drought, shallow soils, shoostring root rot, bark beetles and borers; and with disturbance from construction; borer infested trees should be felled or removed when practical.
  • Pest or Condition: gall phylloxera
    Evidence: spherical galls on twigs and leaf stems.
    Effect: sometimes severe infestations result in early leaf fall.
    Notes: many species of phylloxerans on hickories; only a problem on yard trees.
  • Pest or Condition: fall webworm
    Evidence: gregarious larvae inside increasingly large webs covering foliage.
    Effect: defoliation, sometimes complete.
    Notes: infests many tree species; often prefers hickories; periodically at outbreak densities along Blue Ridge.
  • Pest or Condition: twig girdlers/pruners
    Evidence: smoothly severed branches; may have central gallery.
    Effect: clutter of fallen branches; foliage, twig loss; crown disfigurement.
    Notes: mostly in yard trees; pick up and destroy all fallen branches.

Other periodic hickory defoliator: hickory tussock moth.

Locust

  • Pest or Condition: locust leafminer
    Evidence: adult skeletonizing of lower leaf surface, followed by larval mining.
    Effect: widespread annual browning of locust foliage; growth, vigor reduction.
    Notes: adult beetle overwinters, feeds and lays eggs in spring; larvae feed in common mine initially, then mine separately; two generations.
  • Pest or Condition: locust borer
    Evidence: entrance holes, frass, galleries, poor form.
    Effect: poor growth; riddled stem susceptible to wind breakage.
    Notes: tends to be worse on poor sites; can be reduced through sanitation.
  • Pest or Condition: rimosus heart rot
    Evidence: hard, woody, brown, perennial conk; decayed heartwood.
    Effect: renders wood unusable.
    Notes: very common; not lethal; remove infected trees.

Maples

  • Pest or Condition: Verticillium wilt
    Evidence: leaf stunting, chlorosis, scorch, death; green to brown sapwood stain.
    Effect: branch mortality, sparse foliage, slow growth or tree mortality.
    Notes: affects many woody plants; susceptibility varies among maple species;
    usually begins in roots; nitrogen fertilization can sometimes arrest disease.
  • Pest or Condition: yellow-bellied sapsucker
    Evidence: horizontal row(s) of more or less uniform holes in bark.
    Effect: bark disfigurement, sap flow; fungus infection, staining of wood.
    Notes: bird frequently returns to same trees; feeds on sap, occasionally on insects, buds,
    cambium; hundreds of tree species affected; favorites include pines, hemlock, birches, beeches, aspens, maples.

Occasional maple defoliator in eastern Virginia: whitemarked tussock moth.

Oaks

  • Pest or condition: defoliators (many species)
    Evidence: partial to complete leaf loss any time after spring bud swell.
    Effect: growth, vigor reduction in rough proportion to leaf loss and time of year.
    Notes: early season, heavy defoliation results in refoliation, which reduces food reserves and predisposes tree to secondary pests; can lead to mortality; proper fertilization will help weakened yard trees recover; less impact from late season defoliators. Among the major oak defoliators are fall cankerworm, oak skeletonizer, oak leaftier, gypsy moth, forest tent caterpillar, buck moth, variable oakleaf caterpillar, scarlet oak sawfly, linden looper.
  • Pest or condition: decline
    Evidence: progressive crown dieback from top down and outside in; premature leaf coloration; attacks of secondary organisms, especially shoostring root rot and two-lined chestnut borer.
    Effect: decline over several years, often leading to mortality.
    Notes: episodes have been associated with advanced age, drought, shallow soils, early season defoliating insects and disturbance from construction.
  • Pest or condition: galls
    Evidence: abnormal growths on leaves, twigs, roots.
    Effect: usually none; can lead to early leaf fall, stem breakage.
    Notes: hundreds of kinds on oaks alone; most caused by insects.
  • Pest or condition: leaf blister
    Evidence: convex/concave distortions of leaf blade; a few spots to whole leaf.
    Effect: can lead to partial defoliation.
    Notes: shows up early in season; sometimes widespread.
  • Pest or condition: shoestring root rot
    Evidence: black, string-like rhizomorphs between dead bark and wood
    Effect: usually accelerates decline and death of trees weakened by other agents
    Notes: many species of varying virulence; ubiquitous; also causes decay
  • Pest or condition: borers
    Evidence: holes, frass, sap flow, galleries, bark irregularities.
    Effect: wood product defect and degrade; can lead to stem breakage.
    Notes: development often takes more than one year; heavily infested brood trees timber
    stands should be felled.
  • Pest or condition: scale insects
    Evidence: presence of sooty mold; scale covers; bark abnormalities; tree decline.
    Effect: generally innocuous in forest stands; can be lethal to yard trees.
    Notes: natural enemies usually effective; heavy infestations on yard trees should be suppressed; horticultural oils effective.
  • Pest or condition: anthracnose
    Evidence: small to large, brown patches on succulent leaf tissue; sometimes causes distortion; patches often bounded by veins.
    Effect: can cause partial defoliation, twig dieback, reduced growth.
    Notes: weather related; no practical treatment; susceptibility varies among species.
  • Pest or Condition: oak wilt
    Evidence: leaf wilting, color change to yellow, bronze, tan; leaf drop; sap stain.
    Effect: tree mortality, particularly among the red oak group.
    Notes: found west of Blue Ridge; can kill tree quickly; moves slowly tree-to-tree.
  • Pest or condition: periodical cicada
    Evidence: mass emergence, singing; oviposition wounds leading to twig mortality.
    Effect: damage to fruit bearing branches; partial defoliation; some growth loss.
    Notes: up to several broods per county, each on a different 17- or 13-yr. cycle.
  • Pest or condition: twolined chestnut borer
    Evidence: dieback; mortality; D-shaped exit holes; winding galleries.
    Effect: infestations often begin in top and move downward; intersecting galleries in outer
    sapwood and inner bark tend eventually to girdle and kill tree.
    Notes: frequently found in trees weakened by defoliation and infected by shoestring root rot.
  • Pest or Condition: acorn feeders
    Evidence: empty or damaged acorns.
    Effect: poor to no seedling development; loss of mast for wildlife.
    Notes: many species of insects, mostly weevils, destroy a high percentage of acorn crops annually; can have a major impact on regeneration, wildlife.

Sycamore

  • Pest or Condition: anthracnose
    Evidence: emerging leaves turn dark brown; larger leaves with brown patches.
    Effect: leaf fall; thin crowns, twig dieback.
    Notes: very common; early symptoms easily confused with freeze injury.
  • Pest or Condition: lace bugs
    Evidence: insects clustered under leaves; foliage stippled to almost entirely brown.
    Effect: discoloration, early leaf fall.
    Notes: adult lace bugs flat, whitish with lacelike wings; many species; most have two
    generations a year; stay on undersurface of leaves.

Other common sycamore defoliator: sycamore tussock moth.

Yellow Poplar

  • Pest or condition: leaf weevil
    Evidence: multiple, oval or crescent-shaped holes, mining in leaves; defoliation.
    Effect: repeated partial defoliations weaken trees.
    Notes: a periodical problem in southwestern counties; often over large areas.
  • Pest or condition: Columbian timber beetle
    Evidence: entrance holes about 2 mm in diameter; exude frass and sap; branched tunnels into heartwood.
    Effect: galleries and associated stain devalue wood; infestation can build over time
    Notes: ambrosia beetle -- food is fungus grown in galleries; does not eat wood.
  • Pest or condition: aphids
    Evidence: profuse honeydew, often with sooty mold beneath infested trees.
    Effect: nuisance from honeydew, sooty mold on lawn furniture, sidewalks, cars, etc., and from ants, wasps, bees attracted to honeydew.
    Notes: severe infestations can cause distortion of succulent tissues; some aphids cause galls; virtually all tree species play host to aphids.

Last modified: Thursday, 06-Nov-2014 10:23:25 EST