Tree Pests & Diseases
Mountain Ash Tree Maintenance
Mountain Ash is valued for berries, flowers, and fall color, but it can struggle in hot Front Range conditions. Common issues include fire blight, borers, aphids, leaf spot, and drought stress.
- Species
- Mountain Ash Tree
- Botanical Name
- Sorbus spp.
- Group
- Ornamental Trees
- Tracked Problems
- 7
Seasonal Calendar
| Problem | Type | Active Season |
|---|---|---|
| Fire blight | Bacteria | Spring–Summer |
| Leaf spot | Fungus | Spring–Summer |
| Scale insects | Insect/scale | Spring crawlers; visible year-round |
| Aphids | Insect | Spring–Fall |
| Borers | Insect/borer | Summer |
| Sunscald / heat stress | Abiotic | Summer–Fall |
| Winter injury | Weather | Winter–Spring |
Pest & Disease Guide
Fire Blight
Common symptoms
- Blackened shoot tips
- Wilted blossoms
Treatment & management
- Prune infected tissue
- Sanitize tools
Leaf Spot
Common symptoms
- Leaf lesions
- Early drop
Treatment & management
- Clean up leaves
- Improve airflow
Scale Insects
Common symptoms
- Bumps on stems
- Canopy thinning
Treatment & management
- Dormant oil
- Treat crawler stage
Aphids
Common symptoms
- Honeydew
- Leaf curling
Treatment & management
- Rinse foliage
- Encourage predators
Borers
Common symptoms
- Exit holes
- Dieback
Treatment & management
- Reduce stress
- Protect trunk
Heat Stress
Common symptoms
- Scorch
- Early fall color
Treatment & management
- Deep watering
- Protected planting location
Winter Injury
Common symptoms
- Tip dieback
- Bark injury
Treatment & management
- Prune deadwood in spring
- Avoid late fertilization
When to Worry
- Repeated fire blight
- Heavy dieback
- Borer activity
Mostly Cosmetic
- Minor leaf spots
- Light aphids
- Some scorch in heat
Notes
These can lead to major decline in warm Colorado sites.
These often improve with watering and seasonal care.
Related Resources
Related Services
Great Western Tree Care
When you want a professional opinion
The Root exists to help you understand your landscape. When a tree needs hands-on evaluation, a Great Western arborist can look at it in person.