Diagnosing Common Tree Diseases and Insect Damage

Healthy, well-sited trees resist pests. When problems appear, they're often linked to environmental stress. Here's a diagnostic guide by damage type.

Leaf Damage

Entire leaf eaten except midvein: Caterpillars, sawflies, or webworms.
Holes in flowers: Rose chafers, Japanese beetles, false Japanese beetles.
Notched leaf margins: Black vine weevils.
Circular holes in leaf edges: Leaf cutter bees.
Random holes: Beetles, grasshoppers, weevils.
Skeletonized leaves: Japanese beetles.
White tunnels: Leaf miners.
Leaf curling/puckering: Mites injecting toxins.
White powder: Powdery mildew (surface fungi).
Leaf spots with concentric rings: Fungal leaf spot.
Orange spots: Rust (rarely fatal).

Root Damage

Root rot: Fungi turn roots black/soft. Early signs: wilting, stunting. Caused by overly wet or dry soil.

Stem, Trunk, and Branch Damage

Blackened, dying new shoots: Blight.
Sunken/swollen dead areas (target-shaped): Cankers (enter via wounds).
Swollen galls on trunk/branches: Block nutrient flow.
Dense cluster of new growth (witches'-broom): Cut off to prevent spread.

Four Tips for Safe Pest Management

1. Think before treating. Damage is often cosmetic; healthy ecosystems self-correct.
2. Plant diverse species. Pests target specific groups; diversity limits spread.
3. Choose site-appropriate plants. Thriving plants resist pests naturally.
4. More isn't better. Excess water, fertilizer, or mulch causes problems.