Tree Disease and Insect Guide for Conifers

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).

Eastern Hemlock

• woolly adelgid, spider mites, drought

Eastern Redcedar

• cedar-apple rust, bagworm, annosum root rot, Phomopsis blight

Eastern White Pine

• white pine weevil, procerum root disease, pine bark adelgid, white pine blister rust, introduced pine sawfly, Pityogenes hopkinsi (bark beetle), eriophyid mites, white pine aphid, ozone injury, deicing salt injury, adverse site, physiological needle blights

Fraser Fir

• Phytophthora root rot, balsam twig aphid, balsam woolly adelgid, eriophyid bud, mites, spider mites, freeze injury

Southern Yellow Pines

• regeneration weevils, bark beetles, Nantucket pine tip moth, pine webworm, annosum root rot, stem rusts, pitch canker, Atropellis canker and Diplodia blight, needle cast, sawflies, eastern pine looper, pine spittlebug, voles

Spruces

• spider mites, adelgid twig galls, white pine weevil, adverse climate/weather

Conifers

Eastern Hemlock

• Pest or Condition: woolly adelgid
  Evidence: white, cottony masses on undersides of branches, especially Feb.-May.
  Effect: gradual discoloration followed by defoliation, decline, mortality.
  Notes: treat valuable yard trees with horticultural oil, insecticidal soap or systemic insecticide.
• Pest or Condition: spider mites
  Evidence: older foliage turns gray-green, drops; newer foliage stippled near center.
  Effect: defoliation, vigor loss.
  Notes: common in yard trees; use hand lens to see fine silk, eggs, adults or strike branch over white surface to dislodge mites; treat ornamentals with miticide as soon as infestation evident.
• Pest or Condition: drought
  Evidence: decline, mortality; hemlock borer infestations following drought.
  Effect: usually fairly synchronous regional decline and mortality.
  Notes: most mortality often along stream banks.

Eastern Redcedar

• Pest or Condition: cedar-apple rust
  Evidence: orange, gelatinous fruiting structure in spring, dries to woody gall.
  Effect: sometimes kills portion of twig beyond gall.
  Notes: can cause significant disease on alternate host apple trees.
• Pest or Condition: bagworm
  Evidence: tough, silk-and-needle bags hanging from host foliage; defoliation.
  Effect: defoliation can be severe and repeated, often ruins yard trees.
  Notes: control by removing, disposing of bags if practical; chemical suppression
  should be applied early, when bags are very small; feeds on many species.
• Pest or Condition: annosum root rot see Yellow Pines
• Pest or Condition: Phomopsis blight
  Evidence: dead branch tips with grayish band at base where fruiting bodies occur.
  Effect: can kill seedlings; may invade stem and cause canker.
  Notes: common in nurseries, yard trees; affects succulent tissues; dead tips persist.
  

Eastern White Pine

• Pest or Condition: white pine weevil
  Evidence: wilted/dead/infested terminal.
  Effect: kills tree top only; also infests Norway spruce.
  Notes: spray Christmas tree plantation in late March if 5% or more trees infested the previous year; prune out infested terminals in June before weevils exit; tie side branch in upright position if height growth and form are important.
• Pest or Condition: procerum root disease
  Evidence: chlorosis, wilting, resinosus on bole, basal canker, blue-black basal sapwood stain (one or all in any combination).
  Effect: kills tree.
  Notes: uncommon in natural stands; remove infected tree and roots where practical; do not replace with another white pine; do not plant white pine in poorly drained soils.
• Pest or condition: pine bark adelgid
  Evidence: bole with light to heavy white, cottony covering.
  Effect: prolonged infestation can be associated with bark disease, tree mortality.
  Notes: natural controls usually effective; can be suppressed with insecticides.
• Pest or condition: white pine blister rust
  Evidence: branch/bole cankers with orange fruiting bodies in spring.
  Effect: stem deformity; eventual mortality.
  Notes: almost exclusively west of Blue Ridge; significant problem only in high hazard areas; conduct preplanting exam to locate and eliminate alternate host plants (i.e. currants and gooseberries, genus Ribes).
• Pest or Condition: introduced pine sawfly
  Evidence: larvae; defoliation from up to three generations; cocoons on vegetation.
  Effect: eventually consume both old and new needles; reduce growth.
  Notes: only sawfly on white pine that spins cocoon above ground; natural enemies usually prevent extended outbreaks.
• Pest or condition: Pityogenes hopkinsi (bark beetle)
  Evidence: tiny, frass-filled entrance holes in smooth bark of stem or branches.
  Effect: portends tree mortality.
  Notes: infests slash or trees weakened by other agents.
• Pest or condition: eriophyid mites
  Evidence: small portion to whole crown gradually turns off-green to yellowish.
  Effect: needle loss; weakens tree.
  Notes: cigar-shaped mites too small to see without hand lens and good light, look between needles near base; symptoms progress quickly; infested Christmas trees should be treated immediately.
• Pest or Condition: white pine aphid
  Evidence: shiny, dark aphid with white dorsal stripe; rows of dark eggs on needles.
  Effect: heavy infestations can reduce growth of individual branches, small trees.
  Notes: hatching eggs can be nuisance on Christmas trees.
• Pest or condition: ozone injury
  Evidence: tip to most of needle light yellow.
  Effect: probable growth reduction.
  Notes: sharp transition between affected tip and unaffected base of needle; small percentage of trees exhibit symptoms owing to genetic predisposition.
• Pest or Condition: deicing salt injury
  Evidence: roadside foliage scorch, defoliation, dieback, decline.
  Effect: repeated application and gradual accumulation can lead to mortality.
  Notes: injury occurs both through soil and foliage contact with splashed water or salt in blown roadside dust; tolerance to salt varies greatly among species.
• Pest or condition: adverse site
  Evidence: poor growth, thin crown, chlorosis.
  Effect: low vigor, unhealthy appearance, mortality.
  Notes: white pine has been planted as an ornamental or screen in many places where it does not occur naturally; sometimes it does well in such places but it should not be planted in poorly drained soils or in the hottest and driest regions of Virginia.
• Pest or condition: physiological needle blights
  Evidence: orange to reddish-brown tips on newest foliage; or yellowing and shedding of older needles especially in top third of tree; buds healthy.
  Effect: no lasting effect on otherwise healthy trees.
  Notes: devalues Christmas trees; weather related, no treatment available.

Fraser Fir

• Pest or condition: Phytophthora root rot
  Evidence: foliage turns brown; can be more gradual on larger trees.
  Effect: tree mortality.
  Notes: avoid planting in poorly drained soils; spreads readily through infected soil.
• Pest or condition: balsam twig aphid
  Evidence: needles twist, particularly on branch tips, to reveal silvery undersurface.
  Effect: alters tree appearance; heavy infestations can stunt growth.
  Notes: infested Christmas trees should be sprayed when buds swelling in spring.
• Pest or condition: balsam woolly adelgid
  Evidence: top growth stops; gouty branch swellings; white flocculence on bole.
  Effect: tree decline and mortality.
  Notes: individual trees can be protected with thorough spray coverage.
• Pest or condition: eriophyid bud mites
  Evidence: buds enlarge and flatten out.
  Effect: stops branch growth.
  Notes: treat when buds swell in spring.
• Pest or condition: spider mites
  Evidence: older needles gradually lose healthy color; mites, silk visible with lens.
  Effect: heavy infestations can cause needle drop.
  Notes: treat when mites present on significant percentage of foliage.
• Pest or condition: freeze injury
  Evidence: new growth, young cones turn brown; succulent shoots droop.
  Effect: growth loss.
  Notes: avoid planting in frost pockets.

Southern Yellow Pines

• Pest or Condition: regeneration weevils
  Evidence: chewed/girdled stem/twig on small trees/branches in spring and fall
  Effect: kills or weakens seedlings; can cause branch flagging on larger trees
  Notes: plant insecticide treated trees when reforesting harvested area that was 10% or more pine and was cut or site prepared after May, or spray seedlings after planting, or delay planting for one full growing season; feeding injury can be under ground; affects all pine species.
• Pest or condition: bark beetles (southern pine, turpentine, Ips)
  Evidence: pitch tubes, galleries, fading crowns, fallen frass, fallen green needles
  Effect: tree mortality from successful attacks; sometimes only top kill from Ips
  Notes: periodic southern pine beetle outbreaks cause severe local to regional
  pine mortality; turpentine beetles usually attack injured or weak trees, low density
  attacks sometimes don't kill tree; Ips beetles tend to attack only stressed trees; all pines affected
• Pest or Condition: Nantucket pine tip moth
  Evidence: dead, resinous buds, branch tips.
  Effect: delayed growth of affected branch or terminal; temporary deformity.
  Notes: problem mostly for small trees; multiple generations; tends to be more severe where site preparation intensive.
• Pest or condition: pine webworm
  Evidence: frass-filled, silk webbing on top or entire seedling; defoliation.
  Effect: weakens tree, retards growth; can contribute to seedling mortality.
  Notes: very common, particularly in first growing season; no practical control.
• Pest or condition: annosum root rot
  Evidence: poor growth and color; eventual mortality, increasing over time; small, rough, irregular conk at ground line; resin soaking of infected roots; also kills eastern redcedar if present.
  Effect: gradual mortality, spreads to neighboring trees through root grafts, stumps.
  Notes: severe only in deep, well drained sands; do not thin heavily infected stands on high hazard sites, harvest when practical.
• Pest or condition: stem rusts
  Evidence: globular or spindle shaped swelling on branch; canker on bole.
  Effect: stem deformity; can result in mortality of portions beyond, above infection.
  Notes: minor economic importance in Virginia; rust fungi have alternate hosts.
• Pest or condition: pitch canker
  Evidence: branch, bole canker with resin flow; wood resin-soaked; shoot dieback.
  Effect: dieback, deformity, poor growth; sometimes eventual mortality.
  Notes: top dieback common symptom on loblolly; avoid branch and bole injuries.
• Pest or condition: Atropellis canker and Diplodia blight
  Evidence: small, resinous branch or stem cankers; wood resin-soaked/dark stained.
  Effect: dieback or deformity.
  Notes: can be separated from pitch canker by dark staining of wood; common problems on Scotch pine Christmas trees; can be spread by shearing.
• Pest or condition: needle cast
  Evidence: older foliage turns some shade of yellow to brown or gray-brown; often
  mottled or banded; dark fruiting bodies sometimes evident.
  Effect: discoloration, early loss of older needles.
  Notes: occasionally prevalent over large area; much individual tree variability; many species of fungi cause needle cast; Christmas and ornamental trees can be protected by fungicides.
• Pest or condition: sawflies
  Evidence: spring defoliation of older needles on branch to whole tree.
  Effect: growth reduction; rarely mortality.
  Notes: larvae (several species) feed gregariously; periodic, large population
  fluctuations; tend to occur in patches rather than uniformly over region;
  many natural control agents usually effective.
• Pest or Condition: eastern pine looper
  Evidence: ash-gray moths in understory in May and June; larvae feed into late fall.
  Effect: defoliation, growth reduction of loblolly pine.
  Notes: most prevalent in coastal plain, occasionally at high population densities.
• Pest or Condition: pine spittlebug
  Evidence: spittle mass with immature bug inside.
  Effect: can enable invasion of fungi.
  Notes: adults feed on same hosts, but don't produce spittle.
• Pest or condition: voles
  Evidence: small trees turn from yellow to brown; feeding injury evident at base.
  Effect: usually tree mortality.
  Notes: feeding sometimes below ground; usually associated with snow cover;
  worse where sod, other vegetation dense; can be partially prevented by
  keeping sod killed/mowed back.

Spruces

• Pest or Condition: spider mites
  Evidence: foliage turns off-green, then yellow to brown and eventually drops, from bottom up and inside out; eggs, mites, silk visible with hand lens.
  Effect: Gradual defoliation, can lead to mortality.
  Notes: Favored by cool, dry weather; particularly common on Alberta spruce; treat with miticide, horticultural oil when discovered.
• Pest or Condition: adelgid twig galls
  Evidence: pineapple shaped swellings on twigs.
  Effect: disfigures ornamentals.
  Notes: more than one species; adults, eggs near bud bases; can suppress with
  dormant oil spray.
• Pest or Condition: white pine weevil on Norway spruce - see Eastern White Pine
• Pest or Condition: adverse climate/weather
  Evidence: poor growth and color, infection and infestation by secondary agents.
  Effect: transplanting failure; poor growth; mortality.
  Notes: many places in Virginia are too hot and dry for spruces to remain healthy.
  

Last modified 2006-10-10