Fungus Gnats Treatment

How to know it's fungus gnats

Small dark flies drifting up from the soil when you water, and a scattering of them on the window. The adults are harmless. The larvae are not — they're translucent with a black head capsule, they live in the top inch of media, and they feed on organic matter and fine root hairs. Seedlings and fresh cuttings are the ones that actually suffer.

What eats them

Steinernema feltiae nematodes are the standard answer. These microscopic worms move through moist media, enter the larvae, and release a symbiotic bacterium that kills them from the inside. You water them in, and they work below the surface where nothing you spray will reach.

Stratiolaelaps scimitus is a soil-dwelling predatory mite that patrols the top layer of media, eating fungus gnat larvae, thrips pupae and other soil-dwelling pests. It's slower than nematodes but it stays, which makes it the better long-term choice.

Dalotia coriaria, the rove beetle, hunts the same soil layer as both adult and larva. Good in heavier media and in propagation areas where pressure is constant.

The realistic plan

Nematodes to crash the current generation, Stratiolaelaps to hold the ground afterwards. Both target larvae, so the adults you already have will finish their lives and die off over the following week or two — that's expected, not a sign it failed.

Let the surface dry between waterings where the plant will tolerate it. Fungus gnats need damp organic media to breed, and taking that away does half the work for you. The full fungus gnat guide covers dosing and timing.