Red Maple

(Acer rubrum — includes cultivars like ‘October Glory,’ ‘Autumn Blaze’ hybrid, ‘Red Sunset’)

Red Maple is valued for its vibrant fall color and rounded canopy. In Colorado, true Red Maples often struggle due to alkaline soils, drought, and heat. Hybrids perform better but still face chlorosis, scorch, borers, and leaf diseases.

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
Anthracnose / leaf spot Fungus Spring–Summer
Tar spot Fungus Spring infection; visible Summer
Verticillium wilt Fungus Spring–Fall
Chlorosis Abiotic Spring–Summer
Leaf scorch Abiotic Summer–Fall

Pest & Disease Guide (Homeowner-Friendly)

Aphids

Common symptoms
  • Honeydew and sooty mold
  • Leaf curling
  • Attracts ants
Treatment & management
  • Hose off foliage
  • Encourage predators
  • Treat severe infestations

Scale Insects

Common symptoms
  • Bumps on bark
  • Yellowing leaves
  • Branch dieback
Treatment & management
  • Treat crawler stage
  • Horticultural oil
  • Prune infested branches

Maple Borers

Common symptoms
  • Exit holes
  • Boring dust
  • Branch dieback
Treatment & management
  • Reduce stress
  • Deep watering
  • Preventive treatments if needed

Anthracnose / Leaf Spot

Common symptoms
  • Brown blotches
  • Early leaf drop
  • Distorted leaves
Treatment & management
  • Remove infected leaves
  • Improve airflow
  • Usually cosmetic

Tar Spot

Common symptoms
  • Black tar-like spots
  • Mostly cosmetic damage
Treatment & management
  • Rake leaves
  • No chemical treatment typically needed

Verticillium Wilt

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

Chlorosis

Common symptoms
  • Yellow leaves with green veins
  • Poor growth
  • Twig dieback
Treatment & management
  • Iron treatments
  • Improve soil conditions
  • Adjust watering

Leaf Scorch

Common symptoms
  • Brown leaf edges
  • Early drop
  • Heat stress symptoms
Treatment & management
  • Deep watering
  • Mulch base
  • Avoid heat-reflective areas

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Severe chlorosis across canopy
  • Borer exit holes
  • Sudden wilting branches
  • Large-scale early leaf drop
  • Ongoing yearly decline

Red Maples often struggle long-term in Colorado soils and may require soil correction or replacement.

Mostly Cosmetic (monitor only)

  • Light leaf spot
  • Minor aphid activity
  • Occasional scorch
  • Small tar spot areas
  • Early fall color

These are typically seasonal and resolve with proper care.