Norway Maple

(Acer platanoides — includes cultivars like ‘Crimson King,’ ‘Emerald Queen,’ ‘Deborah,’ ‘Royal Red’)

Norway Maple is a widely planted shade tree known for its dense canopy and deep purple-leaf cultivars. In Colorado, it often struggles with alkaline soils, heat stress, chlorosis, verticillium wilt, girdling roots, and several insect pests. It performs best in cooler, moist, well-drained soils.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Aphids Insect Spring–Fall
Scale insects Insect/scale Spring crawlers; visible year-round
Maple borers Insect/borer Summer
Leaf spot / anthracnose Fungus Spring–Summer
Verticillium wilt Fungus Spring–Fall
Chlorosis Abiotic Spring–Summer
Leaf scorch Abiotic Summer–Fall
Girdling roots Structural/abiotic Visible year-round

Pest & Disease Guide (Homeowner-Friendly)

Aphids

Common symptoms
  • Sticky honeydew
  • Sooty mold
  • Leaf curling
Treatment & management
  • Hose-rinse foliage
  • Encourage beneficial insects
  • Treat severe outbreaks

Scale Insects

Common symptoms
  • Hard or cottony bumps
  • Branch dieback
  • Yellowing canopy
Treatment & management
  • Treat crawler stage
  • Apply horticultural oil
  • Prune infested branches

Maple Borers

Common symptoms
  • Exit holes
  • Branch dieback
  • Sawdust/frass
Treatment & management
  • Reduce stress
  • Deep water during heat
  • Preventive sprays if needed

Anthracnose / Leaf Spot

Common symptoms
  • Brown blotches
  • Early leaf drop
  • Distorted leaves
Treatment & management
  • Rake leaves
  • Improve airflow
  • Rarely needs treatment

Verticillium Wilt

Common symptoms
  • One-sided wilting
  • Sapwood discoloration
  • Progressive dieback
Treatment & management
  • No cure
  • Prune affected limbs
  • Support tree vigor

Chlorosis

Common symptoms
  • Yellow leaves with green veins
  • Reduced growth
  • Thinning canopy
Treatment & management
  • Iron injections
  • Soil treatment
  • Improve drainage

Leaf Scorch

Common symptoms
  • Brown crispy edges
  • Early leaf drop
  • Heat stress damage
Treatment & management
  • Deep water every 2–3 weeks
  • Maintain mulch
  • Avoid hot exposures

Girdling Roots

Common symptoms
  • One-sided decline
  • Trunk constriction
  • Poor canopy density
Treatment & management
  • Expose root flare
  • Remove girdling roots (professional)
  • Long-term correction needed

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Sudden one-sided wilting
  • Severe chlorosis with decline
  • Borer holes or frass
  • Heavy scale infestation
  • Progressive canopy thinning
  • Trunk constriction from roots

These issues often require professional arborist evaluation.

Mostly Cosmetic (monitor only)

  • Light leaf spot
  • Minor scorch
  • Small scale patches
  • Occasional aphids
  • Early color change in drought

These are typically seasonal and resolve with proper care.