Colorado Blue Spruce

(Picea pungens)

Evergreen conifer with stiff, blue-gray needles. Prefers full sun. Commonly stressed in Colorado’s dry, urban environments, which increases vulnerability to pests and diseases.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Spruce spider mite Insect/mite Spring & Fall
Spruce aphid Insect Late Winter–Spring
Ips bark beetle Insect/borer Late Spring–Summer
Rhizosphaera / Stigmina needle cast Fungus Spring infection, symptoms mid–late summer
Cytospora canker Fungus Year-round (visible mostly in Summer–Fall)

Pest & Disease Guide (Homeowner-Friendly)

Spruce spider mite

Common symptoms
  • Inner needles look dull, stippled, then bronze
  • Fine webbing
  • Premature needle drop
  • Paper Test: tap a branch over white paper—moving dots = mites
Treatment & management
  • Confirm with tap test
  • Professional miticide sprays (spring/fall)
  • Deep, infrequent watering; avoid chronic drought stress

Spruce aphid

Common symptoms
  • Sticky needles (honeydew)
  • Sooty mold
  • Localized thinning
Treatment & management
  • Systemic insecticides (product-dependent)
  • Support natural predators
  • Avoid heavy nitrogen fertilizers

Ips bark beetle

Common symptoms
  • Sudden browning of entire sections
  • Fine boring dust around bark cracks
  • Small, round exit holes
Treatment & management
  • Preventive trunk sprays (licensed applicators)
  • Remove severely infested trees
  • Keep tree watered and unstressed—drought is the #1 risk factor

Rhizosphaera & Stigmina needle cast

Common symptoms
  • Lower branches thin first
  • Needles turn purple-brown
  • Black fruiting dots can appear on needles
Treatment & management
  • Fungicide sprays in spring (pros only)
  • Increase airflow: prune interior, avoid overcrowding
  • Reduce overhead irrigation

Cytospora canker

Common symptoms
  • White resin patches on limbs
  • Branches die from the tip inward
  • Often starts on lower limbs
Treatment & management
  • Remove infected limbs back to the branch collar
  • Sanitize pruning tools
  • Improve vigor—watering, mulch, avoiding injury (no chemical cure)

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Large sections of the tree suddenly brown out
  • Resin (“pitch”) oozing from many branches
  • The top begins dying back
  • Bark dust or small round exit holes appear (possible beetles)

Mostly Cosmetic (monitor)

  • Only older, inner needles shed (normal needle drop)
  • A few lower branches thin while the canopy stays full
  • Light aphid activity with no dieback