Scotch Pine

(Pinus sylvestris)

A widely planted landscape pine recognized by its orange upper bark and short twisted needles. Scotch Pine grows well in Colorado but is highly vulnerable to Zimmerman pine moth, Diplodia tip blight, pine wilt nematode, needle scale, and drought stress.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Zimmerman pine moth Insect/borer Late Summer–Fall eggs; Spring larval damage
Pine needle scale Insect/scale Crawler stage in Spring; visible year-round
Diplodia (Sphaeropsis) tip blight Fungus Spring infection
Dothistroma needle blight Fungus Spring infection; symptoms Summer–Fall
Pine wilt nematode Nematode Summer–Fall
Environmental drought stress Abiotic Summer–Fall

Pest & Disease Guide (Homeowner-Friendly)

Zimmerman Pine Moth

Common symptoms
  • Branch tips die back
  • Pitch masses at branch whorls
  • Larval tunneling weakens structure
Treatment & management
  • Timed insecticide in early spring (pros)
  • Remove heavily infested limbs
  • Keep tree well-watered to reduce stress

Pine Needle Scale

Common symptoms
  • White elongated scale on needles
  • Yellowing, thinning canopy
  • Reduced vigor over time
Treatment & management
  • Horticultural oil in late winter/early spring
  • Treat crawler stage in spring (pros)
  • Deep watering and mulch improve resilience

Diplodia (Sphaeropsis) Tip Blight

Common symptoms
  • Browning of new candles
  • Resin droplets on cones
  • Lower branches thin first
Treatment & management
  • Fungicide applications in spring for high-value trees
  • Remove infected shoots and cones
  • Improve spacing and reduce stress

Dothistroma Needle Blight

Common symptoms
  • Red bands and brown needle tips
  • Premature needle drop
  • Lower canopy thinning
Treatment & management
  • Fungicide in spring (two treatments recommended)
  • Avoid overhead irrigation
  • Clean up fallen needles

Pine Wilt Nematode

Common symptoms
  • Rapid browning of entire tree (often weeks)
  • Needles turn dull green → tan → brown
  • Most common on Scotch Pine
Treatment & management
  • No chemical cure
  • Remove tree promptly to prevent spread
  • Replace with more resistant species (e.g., Austrian or Ponderosa pine)

Environmental Drought Stress

Common symptoms
  • Needle tip burn
  • Early needle shed
  • Overall reduced vigor
Treatment & management
  • Deep water every 3–4 weeks in dry months
  • Maintain 2–4" mulch ring
  • Avoid soil compaction and root damage

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Entire tree browns suddenly → possible pine wilt nematode
  • Branch whorl pitch masses or flagging tips (Zimmerman moth)
  • Severe lower-branch dieback
  • Widespread needle loss or red-banded needles
  • Heavy scale infestation across canopy

These issues require professional diagnosis and prompt treatment.

Mostly Cosmetic (monitor only)

  • Normal fall shedding of older needles
  • Light needle cast after wet springs
  • Minor scale patches on isolated branches
  • Small amounts of needle tip browning from heat/drought

Often resolved through improved watering and reduced stress.