Greenhouse Whitefly Control: Dormant Oil and Seasonal Strategy

Severe whitefly infestations in Pennsylvania gardens can seem hopeless, but hard winters usually eliminate them outdoors. The key is breaking the cycle before they establish.

Lifecycle Insight

Whiteflies overwinter as eggs or nymphs on protected plants. In greenhouses or mild winters, they survive year-round. Outdoors in Zone 5-6, cold kills most, but early spring arrivals from nearby infested plants or purchased transplants restart populations.

Integrated Management Plan

1. Late winter: Apply dormant horticultural oil to woody plants, evergreens, and perennial crowns to suffocate overwintering stages.
2. Spring planting: Inspect all transplants. Quarantine new plants 1 week.
3. Early summer: At first sign of adults, spray insecticidal oil (e.g., Oil Away, Pyola) weekly for 3 weeks.
4. Ongoing: Use insecticidal soap as needed. Rotate modes of action to prevent resistance.
5. Cultural: Remove heavily infested leaves, avoid excess nitrogen, encourage lacewings/parasitic wasps with nectar plants.

Consistency beats intensity. Early, repeated oil/soap applications prevent explosive growth.