Holly Leaf Blight and Sooty Mold: Insect-Driven Problems

Black Leaves, Webs, and White Larvae on Holly: What's Happening?

A holly bush shows blackened leaves, spider webs, and ½-inch whitish maggot-like larvae. Hosing removed the black coating and webs. The owner asks about insecticide choice.

Diagnosing the Complex

• Black coating = sooty mold: A fungus growing on honeydew (sugary excrement) from sap-sucking insects—likely soft scale, whiteflies, or aphids.
• Webs = spider mites or spider egg sacs: Spider mites produce fine webbing; spiders make larger webs. Both can coexist with sap-feeders.
• Whitish larvae = possibly syrphid fly larvae (beneficial) or scale crawlers: Need magnification to ID.

Treatment Strategy

1. Confirm the pest: Take a sample to a local garden center or Extension office. Misidentification wastes money and harms beneficials.
2. If scale or whitefly: Systemic soil drench with imidacloprid (e.g., Bayer Advanced Tree & Shrub) provides season-long control. Apply per label—expensive but effective.
3. If spider mites: Requires a miticide, not a standard insecticide. Horticultural oil or insecticidal soap works if coverage is thorough.
4. Sooty mold: Will weather off once insects are controlled. No fungicide needed.

Always verify the pest before buying chemicals. A $20 sample diagnosis saves $100 in wrong treatments.