Buckeye

(Aesculus spp.) — Ohio Buckeye, Red Buckeye, Yellow Buckeye, Hybrid Horsechestnuts

Buckeyes are admired for their showy spring flowers, bold palmate leaves, and distinctive nuts. In Colorado, they perform moderately well but can struggle with leaf scorch, leaf blotch, mildew, borers, aphids, and environmental heat stress. Ohio Buckeye and hybrid types tend to handle Colorado’s climate better than European Horsechestnut.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Leaf blotch (Guignardia) Fungus Spring–Summer
Leaf scorch (abiotic) Abiotic Summer–Fall
Powdery mildew Fungus Summer–Fall
Aphids Insect Spring–Fall
Japanese beetles (Front Range) Insect Summer
Borers Insect/borer Summer
Scale insects Insect Spring crawlers; visible year-round
Leaf miner Insect Summer

Pest & Disease Guide (Homeowner-Friendly)

Leaf Blotch (Very Common)

Common symptoms
  • Brown irregular patches
  • Spots may merge
  • Early leaf drop by late summer
Treatment & management
  • Rake leaves and debris
  • Improve airflow via light pruning
  • Fungicide seldom necessary

Leaf Scorch (Major Issue in Colorado)

Common symptoms
  • Browning tips & margins
  • Leaves dry and curl
  • Premature fall color
Treatment & management
  • Deep water every 2–3 weeks in summer
  • Maintain mulch ring
  • Avoid reflective heat & compacted soil

Powdery Mildew

Common symptoms
  • White powdery coating on leaves
  • Distorted new growth
Treatment & management
  • Increase airflow
  • Water roots, not foliage
  • Fungicide only for severe, repeated infections

Aphids

Common symptoms
  • Sticky honeydew
  • Sooty mold
  • Leaf curling
Treatment & management
  • Hose off leaves
  • Encourage lady beetles
  • Systemic insecticide if large colony forms

Japanese Beetles

Common symptoms
  • Skeletonized leaves
  • Clusters of beetles feeding
Treatment & management
  • Hand-pick early morning
  • Avoid JB-attracting plants nearby
  • Professional insecticide if severe

Borers

Common symptoms
  • Exit holes
  • Sawdust-like frass
  • Branch dieback
Treatment & management
  • Avoid stress and trunk wounds
  • Water regularly
  • Preventive sprays (professionally applied) if needed

Scale

Common symptoms
  • Small bumps on twigs
  • Honeydew, black mold
  • Thinning canopy
Treatment & management
  • Dormant oil in late winter
  • Treat crawler stage in late spring
  • Prune heavily infested stems

Leaf Miner

Common symptoms
  • Brown mines/tunnels in leaves
  • Cosmetic browning
  • Rarely causes decline
Treatment & management
  • Remove infested leaves
  • Usually does not require treatment

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Severe scorch every summer despite proper watering
  • Heavy leaf blotch causing near-total defoliation early each year
  • Repeated Japanese beetle attacks thinning the canopy
  • Borer exit holes combined with dieback
  • Progressive thinning of canopy or poor annual growth

These conditions may require professional evaluation and a change in site care.

Mostly Cosmetic (monitor only)

  • Mild leaf blotch or scorch late in summer
  • Light aphid activity with minimal honeydew
  • Occasional mildew on shaded leaves
  • Minor leaf miner trails
  • Early fall color during drought years

These issues typically resolve with good watering habits and leaf cleanup.