Hawthorn Tree
(Crataegus spp.)
Hawthorns are tough ornamental trees with flowers, fruit, and strong wildlife value, but they can develop rust, leaf spot, fire blight, aphids, and scale in Colorado landscapes.
Seasonal Pest & Disease Calendar
| Problem | Type | Active Season |
|---|---|---|
| Fire blight | Bacteria | Spring–Summer |
| Cedar-hawthorn rust | Fungus | Spring–Summer |
| Leaf spot | Fungus | Spring–Summer |
| Scale insects | Insect/scale | Spring crawlers; visible year-round |
| Aphids | Insect | Spring–Fall |
| Spider mites | Mite | Summer |
| Environmental stress | Abiotic | Summer–Fall |
Pest & Disease Guide (Homeowner-Friendly)
Fire Blight
Common symptoms- Blackened shoots
- Crook-shaped tips
- Prune infected branches
- Sanitize tools
Cedar-Hawthorn Rust
Common symptoms- Orange leaf spots
- Fruit spotting
- Reduce nearby juniper sources
- Treat severe cases
Leaf Spot
Common symptoms- Leaf lesions
- Early drop
- Clean up leaves
- Improve airflow
Scale Insects
Common symptoms- Bumps on stems
- Thinning foliage
- Horticultural oil
- Treat crawler stage
Aphids
Common symptoms- Sticky honeydew
- Leaf curling
- Rinse foliage
- Encourage predators
Spider Mites
Common symptoms- Bronzed foliage
- Fine stippling
- Increase irrigation
- Rinse canopy
Environmental Stress
Common symptoms- Scorch
- Poor vigor
- Deep watering
- Mulch base
When to Worry vs. When It’s Cosmetic
When to Worry (action recommended)
- Repeated fire blight
- Heavy rust infection
- Branch dieback
These can affect flowering, fruit, and long-term structure.
Mostly Cosmetic (monitor only)
- Minor leaf spotting
- Light aphids
- Some summer scorch
These often improve with pruning and irrigation.