If a tree looks ‘off’ but you can’t quite say why, scan for these common culprits.
1) Oak wilt
Hosts: All oaks. Red oaks often die within one season. White oaks decline more slowly.
What to look for:
- Red oaks show browning from the tip inward, sometimes with a green midrib.
- White oaks lose leaves gradually and may decline over years.
- Fungal mats under the bark can occur on red oaks.
How it spreads: Through root grafts between nearby oaks and by insects visiting fresh wounds.
Prevention: We typically avoid pruning oaks from April through July. If storms force a cut in that window, paint the wound right away.
Management: Trenching can disrupt root grafts. Systemic fungicide injections may help high-value trees if started early.
2) Apple scab
Hosts: Crabapples and apples. Related fungi can also spot mountain ash leaves.
What to look for:
- Olive-green leaf spots in spring that darken over time.
- Yellowing and premature leaf drop by summer.
- On fruiting apples, dark, scabby lesions on fruit.
Why it lingers: Cool, wet springs favor infection, and the fungus overwinters on leaves.
Prevention: Choose resistant cultivars and clean up leaves in fall.
Treatment: Preventive fungicide sprays in early spring. After symptoms show, focus on sanitation to lower next year’s pressure.
3) Fire blight
Hosts: Crabapple, apple, pear, hawthorn, and other rose family relatives, including mountain ash.
What to look for:
- The classic “shepherd’s crook” at shoot tips.
- Leaves that look scorched but remain attached.
- Bacterial ooze in warm, humid weather.
- Dieback moving from tips into larger wood.
How it spreads: Rain, insects, and contaminated tools during warm, humid stretches.
Prevention: Go easy on spring nitrogen that pushes soft growth. Pick resistant varieties when you can.
Management: Prune 8 to 12 inches below visible symptoms. Disinfect tools between EVERY cut with alcohol or a diluted bleach solution. For severe cases, delay heavy pruning until dormancy.
