Flies & Soil Larvae

The stage that matters is underground

Most of the flies that bother a plant collection spend their damaging life stage in the media, not in the air. Fungus gnats, shore flies and various beetle grubs all lay eggs in moist substrate and do their feeding out of sight. Swatting the adults is satisfying and changes nothing.

What eats them

Steinernema feltiae actively searches moist media for fungus gnat larvae and thrips pupae, enters them, and releases a symbiotic bacterium. The standard choice for houseplants and propagation.

Steinernema carpocapsae is an ambush hunter that waits near the surface for mobile prey. Better for caterpillars, cutworms and borers moving across or just under the surface.

Heterorhabditis bacteriophora ranges deeper and targets beetle grubs — the pest that shows up in outdoor beds and larger containers.

The Triple Blend puts all three strategies in one application, which is the right call when you know something is eating roots but not what.

How to apply them

Nematodes are living organisms and they need moisture to move. Water the media before you apply, mix and apply promptly, and keep the substrate damp for the following days. Avoid direct sunlight during application — UV is what kills them.

They're microscopic, so you get no visual confirmation of the nematodes themselves. You confirm by watching adult numbers on sticky traps over the following two weeks.

For continuous suppression rather than a one-off knockdown, pair them with Stratiolaelaps scimitus, which stays in the media long after the nematodes have done their work.