White Powdery Substance on Plant Leaves: Scale Insects, Not Fungus

Grainy White Powder Between Leaves? It's Likely Scale Insects

A white, cottony or powdery substance deep in leaf axils on a broad-leaved plant with purple flower balls is characteristic of scale insects (e.g., mealybugs, cottony cushion scale), not a fungus. They suck sap, causing yellowing and leaf death.

Identification

• White, waxy, cottony, or powdery deposits in protected areas.
• Underneath: small, immobile insects (scales) or mobile crawlers.
• Honeydew and sooty mold often present.

Control

1. Horticultural oil (dormant or summer rate) – smothers all stages.
2. Insecticidal soap – good for crawlers; repeat weekly.
3. Systemic imidacloprid – soil drench for persistent infestations.
4. Rubbing alcohol – spot-treat with cotton swab.

Follow-Up

• Treat twice, 10–14 days apart.
• Monitor for reinfestation.
• Improve air circulation; avoid excess nitrogen.

Early detection and thorough coverage are key to scale control.