Sooty Mold on Camellia Hedge: Caused by Scale Insects

My camellia hedge has black mildew on leaves, branches, and trunks. It washes off with water but returns. White oil didn't help. It's a hedge, so many plants are affected. Please help.

Diagnosis: Sooty Mold (Secondary to Scale Infestation)

The black coating is sooty mold—a fungus growing on honeydew (sugary excrement) from sap-sucking insects. It's not a primary disease; the insects are the real problem.

Primary Suspect: Scale Insects

• Live under shell-like covers on stems/branches
• Hard to see—often match bark color
• Protected from contact sprays by their shell
• Produce copious honeydew → sooty mold

Effective Treatment: Systemic Insecticide

Imidacloprid soil drench (Bayer Advanced Tree & Shrub Insect Control):

1. Mix with water per label
2. Pour around base of each plant
3. Roots absorb → moves to leaves/stems
4. Scales die when they feed
5. Honeydew stops → sooty mold weathers off naturally

Advantages: No spray drift, protects beneficials, season-long control, easy for hedges.

Supplemental Steps

• Wash off heavy sooty mold with soapy water + hose to improve photosynthesis
• Prune heavily infested/dead branches
• Monitor for ants (they farm scales)—bait if needed
• Reapply soil drench annually in spring

Once scales are controlled, the sooty mold disappears on its own. Your hedge will recover.