Ash Maintenance
Deciduous shade tree common in Colorado landscapes. Ash are highly vulnerable to borers— especially Emerald Ash Borer (EAB)—as well as several native borers, fungal leaf issues, and environmental stress.
- Species
- Ash
- Botanical Name
- Fraxinus spp.
- Group
- Deciduous Trees
- Tracked Problems
- 8
Seasonal Calendar
| Problem | Type | Active Season |
|---|---|---|
| Emerald ash borer (EAB) | Insect/borer | Late Spring–Summer |
| Lilac–ash borer | Insect/borer | Spring–Summer (adult flight) |
| Banded ash borer | Insect/borer | Early Spring |
| Redheaded ash borer | Insect/borer | Spring–Fall |
| Ash bark beetle | Insect/borer | Late Spring–Summer |
| Ash anthracnose | Fungus | Cool, wet Spring |
| Ash rust | Fungus | Spring infection; visible late Spring–Summer |
| Environmental leaf scorch / decline | Abiotic | Summer drought |
Pest & Disease Guide
Emerald Ash Borer (EAB)
Common symptoms
- Thinning canopy
- “D-shaped” exit holes
- Epicormic sprouts at trunk base
- Woodpecker activity & bark flecking
Treatment & management
- Systemic trunk injections (every 2–3 yrs; pros only)
- Treat BEFORE infestation symptoms for best survival
- Remove severely infested trees—beetle spreads quickly
Lilac–Ash Borer
Common symptoms
- Branch dieback
- Clear-wing moth; larvae tunnel in trunk
- Sawdust-like frass at trunk base
Treatment & management
- Preventive trunk sprays in spring (pros)
- Reduce stress: water deeply, avoid wounding trunk
- Remove severely infested limbs
Banded Ash Borer
Common symptoms
- Early spring activity
- Exit holes similar to other borers
- Damage often in recently stressed trees
Treatment & management
- Improve vigor: watering, mulch
- Preventive sprays when needed (pros)
- Typically secondary—manage stress first
Redheaded Ash Borer
Common symptoms
- Tunneling in stressed or newly planted trees
- Round exit holes
- Rapid decline under severe infestation
Treatment & management
- Reduce stress, water deeply
- Professional preventive trunk spray if high risk
- Remove dying trees
Ash Bark Beetle
Common symptoms
- Top-down dieback
- Small pinholes in bark
- Fine boring dust
Treatment & management
- Watering & stress reduction is critical
- Remove dead branches promptly
- Preventive sprays may help in outbreak years
Ash Anthracnose
Common symptoms
- Leaf curling & distortion
- Brown/black blotches
- Early leaf drop in wet springs
Treatment & management
- Usually cosmetic
- Rake/remove leaves
- Improve airflow, avoid overhead irrigation
Ash Rust
Common symptoms
- Orange/yellow swellings on leaves
- Orange spores on leaf undersides
- Premature leaf drop
Treatment & management
- Mostly cosmetic in CO
- Remove fallen leaves
- Fungicide rarely needed
Environmental Leaf Scorch / Decline
Common symptoms
- Browning tips and margins
- Leaves crisp in midsummer
- Often drought or root damage related
Treatment & management
- Deep watering every 2–3 weeks in summer
- Maintain 2–4" mulch ring
- Avoid compacting soil or damaging roots
When to Worry
- Canopy thinning from the top down
- D-shaped exit holes or bark splitting
- Woodpecker damage (flecked bark)
- Entire branches suddenly die mid-summer
- Sprouting from the trunk is increasing
Mostly Cosmetic
- Leaf spots or curling in wet springs (anthracnose)
- Light rust spotting without branch dieback
- Minor scorch during hot, dry periods
- Small amount of early leaf drop in wet years
Notes
These signs suggest borer activity, especially EAB, and require immediate evaluation.
These typically resolve with improved watering and simple cleanup.
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