Fungus Gnats in Houseplants: Sticky Traps, Drier Soil, and Nematodes

Tiny black flies emerging from potted plants in Dayton, Ohio, were identified as dark-winged fungus gnats. Larvae feed on fungi in damp potting mix.

Three-step reduction:

1. Yellow sticky traps in each pot to catch adults.
2. Water less frequently—let the top inch dry out.
3. Beneficial nematodes (Steinernema feltiae) applied to soil to kill larvae. See source and instructions.

This combination brings populations to a tolerable level without chemicals.