Hackberry

(Celtis occidentalis — Common Hackberry)

Hackberry is one of the hardiest and most reliable shade trees for Colorado. It tolerates drought, alkaline soils, wind, urban pollution, and temperature extremes. While generally low-maintenance, Hackberry can experience nipplegall psyllids, witches’ broom, scale, leaf spots, and occasional borer or canker issues.

Seasonal Pest & Disease Calendar

Problem Type Active Season
Nipplegall psyllid Insect Spring–Summer
Hackberry witches’ broom Fungus + insect complex Visible year-round
Scale insects Insect Spring crawlers; visible year-round
Aphids Insect Spring–Fall
Leaf spot / anthracnose Fungus Spring–Summer
Borers (rare unless stressed) Insect/borer Summer
Canker diseases Fungus Spring–Fall
Drought stress Abiotic Summer–Fall

Pest & Disease Guide (Homeowner-Friendly)

Nipplegall Psyllid (Very Common)

Common symptoms
  • Tiny bumps or “nipple galls” on leaves
  • Leaves may be puckered or distorted
  • No long-term harm
Treatment & management
  • No treatment recommended—cosmetic only
  • Rake leaves to reduce next year’s population

Hackberry Witches’ Broom

Common symptoms
  • Dense, broom-like twig clusters
  • Caused by fungus + mites
  • Often harmless but unattractive
Treatment & management
  • Prune out worst clusters in winter
  • Improve vigor with watering & mulch
  • No effective chemical cure

Scale Insects

Common symptoms
  • Sticky honeydew & sooty mold
  • Hard or cottony bumps on twigs
  • Thinning foliage if severe
Treatment & management
  • Treat crawler stage in late spring
  • Horticultural oil in late winter
  • Prune infested branches

Aphids

Common symptoms
  • Honeydew and sooty mold
  • Minor leaf curling
  • Attracts ants
Treatment & management
  • Hose-rinse leaves
  • Encourage predators (lady beetles)
  • Systemic treatments for major outbreaks

Leaf Spot / Anthracnose

Common symptoms
  • Brown blotches or irregular patches
  • Early leaf drop in wet springs
  • Often tree refoliates
Treatment & management
  • Clean up fallen leaves
  • Improve airflow
  • Generally cosmetic—rarely needs treatment

Borers (Flatheaded or Roundheaded)

Common symptoms
  • Exit holes
  • Branch dieback
  • More common in drought-stressed trees
Treatment & management
  • Deep watering during drought
  • Avoid trunk injury
  • Pro pesticide only when confirmed

Canker Diseases

Common symptoms
  • Sunken bark areas
  • Dead patches on twigs or branches
  • Dieback from tips
Treatment & management
  • Prune infected limbs back to collar
  • Sanitize tools
  • Improve vigor—no chemical cure

Drought Stress

Common symptoms
  • Leaf scorch
  • Sparse canopy
  • Early leaf drop
Treatment & management
  • Deep water every 3–4 weeks
  • Maintain mulch ring
  • Avoid soil compaction over roots

When to Worry vs. When It’s Cosmetic

When to Worry (action recommended)

  • Significant branch dieback or top-down decline
  • Multiple expanding cankers on limbs
  • Large areas of bark cracking or peeling
  • Severe scale infestation with black sooty mold
  • Borer exit holes with thinning canopy
  • Repeated early defoliation leading to decline

These conditions may require professional arborist evaluation.

Mostly Cosmetic (monitor only)

  • Nipplegall psyllid bumps (extremely common)
  • Minor witches’ broom clusters
  • Light aphid or scale activity
  • Small leaf spots from wet weather
  • Early yellowing in drought

Most Hackberry issues do not threaten the tree’s health and resolve with normal seasonal care.