Rocky Mountain Juniper

(Juniperus scopulorum)

A hardy native evergreen found throughout Colorado’s foothills and high plains. Highly drought-tolerant and long-lived, Rocky Mountain Juniper is susceptible to juniper scale, cedar–apple rust, twig blights, bark beetles, and root decline from poor drainage.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Juniper scale Insect/scale Spring crawler stage; visible year-round
Juniper twig blight (Phomopsis / Kabatina) Fungus Kabatina: Late Winter–Spring; Phomopsis: Spring–Summer
Cedar–apple rust (Gymnosporangium) Fungus Spring infection; galls visible Winter–Spring
Ips bark beetles (juniper species) Insect/borer Spring–Fall
Spider mites Mite Summer (dry, hot weather)
Root decline (poor drainage, overwatering, compaction) Abiotic Summer–Fall

Pest & Disease Guide (Homeowner-Friendly)

Juniper Scale

Common symptoms
  • White/gray specks on needles
  • Needle yellowing
  • Thinning branches
Treatment & management
  • Treat crawler stage in spring (pros)
  • Horticultural oil in late winter
  • Improve vigor: deep watering during drought

Juniper Twig Blight (Phomopsis / Kabatina)

Common symptoms
  • Tip dieback on branch ends
  • Brown, brittle shoots
  • Often begins on stressed plants
Treatment & management
  • Prune out infected tips (sanitize tools)
  • Increase airflow; avoid overcrowding
  • Fungicide in spring for severe cases

Cedar–Apple Rust

Common symptoms
  • Orange/brown galls on juniper branches
  • Gelatinous orange “horns” in wet spring
  • Cosmetic on junipers; serious on apples/crabapples
Treatment & management
  • Remove galls if reachable
  • Plant apples & junipers apart
  • Fungicide rarely needed for juniper

Ips Bark Beetles

Common symptoms
  • Fine boring dust
  • Small pinholes in bark
  • Branch dieback or whole sections turning brown
Treatment & management
  • Deep watering during drought reduces risk
  • Preventive trunk sprays (pros) in outbreak years
  • Remove and dispose of heavily infested trees

Spider Mites

Common symptoms
  • Foliage turns dull, dusty, or bronzed
  • Fine webbing
  • More severe in hot, dry summers
Treatment & management
  • Hose-rinse foliage periodically
  • Professional miticide if population is high
  • Avoid chronic drought stress

Root Decline (Poor Drainage or Overwatering)

Common symptoms
  • Yellowing/browning foliage not linked to pests
  • Whole-plant thinning
  • Often triggered by clay soil or automatic irrigation
Treatment & management
  • Reduce or correct irrigation
  • Improve soil drainage
  • Mulch lightly—avoid piling against trunk

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Entire branches turn brown suddenly
  • Boring dust or bark pinholes appear (possible Ips beetles)
  • Heavy scale covering needles
  • Progressing twig dieback throughout canopy
  • Chronic yellowing not improved by watering adjustments
  • Galls multiplying rapidly near fruit trees (rust cycle management)

These situations need professional evaluation or timely treatment.

Mostly Cosmetic (monitor only)

  • Small, isolated twig-tip dieback
  • Light scale presence on a few needles
  • Occasional rust galls on branches
  • Minor bronzing from drought or winter desiccation
  • Slight spider-mite activity without widespread damage

Often resolves with improved watering, airflow, and seasonal recovery.