Identifying Black Spots on Bougainvillea Leaves

Identifying Black Spots on Bougainvillea Leaves

A bougainvillea bush developed black droppings on some leaves. The plant otherwise looks healthy.

Black spots on leaf

Entire plant

Diagnosis Steps

1. Rub test: Try to rub the spots off with a finger. If they come off easily, they are likely insect frass (excrement) or the insects themselves (e.g., aphids, scale, caterpillars).
2. Inspect leaves and stems for chewing damage, webbing, or live insects.
3. Check overhead plants—debris may fall from above.

Common Culprits

• Sooty mold: Black fungal growth on honeydew from sap-sucking insects (aphids, whiteflies, scale). Not a disease itself.
• Caterpillar droppings: Dark, pellet-like frass.
• Insect eggs or scales: May appear as small black dots.

Action Plan

• If spots rub off and insects are found, treat with neem oil or insecticidal soap.
• If sooty mold, control the underlying insects; mold will weather away.
• Bring a few affected leaves in a sealed bag to a local nursery for definitive ID.

The plant's overall vigor suggests the issue is manageable and not a systemic disease.