Crabapple Leaf Spots: Likely Fungal Disease, Not Insects

Dark growths on 70% of crabapple leaf undersides are probably a fungal disease (e.g., cedar-apple rust, scab, or powdery mildew), not insects. Insects rarely cover leaves so uniformly.

Next Steps

1. Consult local Cooperative Extension with clear photos (top/bottom of leaves).
2. Search "crabapple leaf diseases" + your state for ID guides.
3. Collect affected leaves in fall—reduce overwintering spores.
4. Consider resistant varieties for new plantings.

Common Culprits

• Cedar-apple rust: Orange spots, gelatinous horns on undersides. Needs juniper host.
• Apple scab: Olive-green to black velvety spots.
• Powdery mildew: White powdery coating.

Fungicides work preventively—timing is critical. Extension office gives local spray schedules.