Oleander Sooty Mold: Sucking Insect Source and Seasonal Control Timing

Spread Pattern

Lori (coastal NC island): black sooty substance on oleanders, started one plant last summer, spread to 2 adjacent + 8 along fence. Ground-up progression. Many more at risk.

Cause: Sucking Insects → Honeydew → Sooty Mold

• Sooty mold = cosmetic fungus on honeydew
• Honeydew from: aphids, scales, mealybugs, whiteflies
• Insects suck phloem sap → excrete sugar-rich honeydew
• Mold blocks light → reduces photosynthesis
• Indirect harm: insect feeding + light reduction

Susceptible Plants

Any plant under/near infested plants. Broadleaf trees, conifers, shrubs, herbs all affected.

Control: Insect Suppression Only

Timing Critical

• Aphids: Early May (East)
• Scales: Late-winter dormant oil (kills overwintering stage)
• Exceptions: Sugar/Japanese maples, hickory, beech, birch, Douglas fir, juniper — dormant oil injury risk → use insecticide at crawler emergence
• Scale crawler timing: Species-specific — check county Extension

Additional Notes

• Prune dead/dying branches (prevents secondary pathogens)
• Sooty mold persists after insects gone
• Insect feeding may kill plant parts before mold appears