Fungus gnats
categories: Fact Sheet Nuisance Pests
revision date: 2025-12-22 04:17
Photo by: Ken Gray
Biology
Fungus gnats are small (1/8 inch) gray-black flies often noticed around houseplants and windows. Most species inhabit fungi or dead plant material, but a few species have maggots that injure plant roots. Even non-pest species can injure plants if their preferred food source of decaying plant material is not available.
Fungus gnats are very dependent on high moisture levels in the soil and are particularly troublesome when overwatering occurs.
Management Options
Use Integrated Pest Management (IPM) for successful pest management.
Non-chemical Management
Select non-chemical management options as your first choice!
- Do not overwater houseplants. Overwatering provides ideal breeding conditions.
- Use houseplant soil moisture meters to more accurately monitor soil moisture levels. Let soil “dry down” within reasonable limits between watering.
- Hang sticky yellow traps over houseplants as a first step in suppressing heavy adult populations.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Be sure to remove breeding sites.
- Pesticide applications are not recommended.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.
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