Fungus Gnats

Also known as: Sciaridae, soil gnats

Identification

Adults: tiny dark flies (2-3mm) hovering near soil surface and windows. Larvae: translucent white, 5mm, in top inch of soil. Yellow sticky traps catch adults.

Damage

Larvae feed on fungi, organic matter, and roots in soil. Adults are harmless nuisance fliers. Heavy larval infestations damage seedling roots.

Best Organic Solutions (Ranked)

Solutions ranked by reliability tier — start with Tier A options.

Bacillus thuringiensis (Bt) Tier A

Bti strain — drench soil with Mosquito Bits tea

Beneficial Nematodes Tier A

Steinernema feltiae hunts larvae in soil

Diatomaceous Earth (DE) Tier A

Top-dress soil surface to kill emerging adults

Biological Controls

Hypoaspis (Stratiolaelaps) miles predatory mites in soil. Rove beetles.

Prevention

Allow soil to dry between waterings — larvae need moist organic soil. Avoid overwatering. Use well-draining potting mix. Bottom-water plants.

Common Mistake

Killing adults only (sticky traps, sprays) while ignoring larvae in soil. The lifecycle is in the soil — treat the soil.