Fungus Gnats on peace lily
What's Happening
Fungus gnats (Bradysia spp., Lycoriella spp.) infest peace lily soil when the top 1-2 inches remain continuously moist, creating ideal breeding conditions. Adult gnats lay 100-200 eggs in organic-rich, damp soil where larvae hatch within 4-6 days. Larvae feed on decaying organic matter, fungal hyphae, and fine root hairs for 10-14 days before pupating. While primarily nuisance pests, heavy infestations (50+ larvae per pot) damage root systems and create entry points for root rot pathogens. Peace lilies' preference for consistently moist (not wet) soil creates a narrow moisture management challenge.
How to Fix It
- 1
Allow top soil layer to dry completely for 3-5 days—gnat larvae require moisture to survive
- 2
Apply Bacillus thuringiensis israelensis (BTI) drench (Mosquito Bits/Dunks) to soil—kills larvae within 24 hours, harmless to plants
- 3
Place yellow sticky traps at soil surface to capture emerging adults and monitor population
- 4
Top-dress soil with sand or diatomaceous earth to prevent re-infestation
- 5
Repot in fresh sterile mix if infestation exceeds 20+ adults on sticky traps weekly
How to Prevent It
Allow top 1-2 inches of soil to dry between waterings—peace lily can tolerate slight surface drying without harm. Use well-draining potting mix with 20-30% perlite to improve aeration. Cover soil surface with 1-inch sand or diatomaceous earth layer to block egg-laying. Empty saucers promptly after watering. Quarantine new plants and repot in sterile mix to eliminate egg contamination.