About this product
Lift a houseplant or a seed tray and a small cloud of dark flies rises up. Those are sciarid flies, better known as fungus gnats, and they are the most common indoor and propagation pest in the country.
The adults are a nuisance. The larvae are the actual problem. They live in the top 3 to 5cm of compost, feeding on organic matter, fungal mycelium and tender roots. On established houseplants that means stunted growth and yellowing leaves. On seedlings and cuttings it is far worse, because the larvae sever fine roots and feed on the stem base, and a whole tray of carefully raised seedlings can be lost in days. If you sow indoors, take cuttings, keep houseplants or grow microgreens, this is the treatment that addresses the damage rather than the annoyance.
The mix is Steinernema feltiae and Steinernema carpocapsae. Watered into the compost as a drench, they swim through the films of water around soil particles and locate the larvae by sensing the carbon dioxide and waste products they give off. They enter through the larva's breathing pores and mouth, release symbiotic bacteria that kill it within hours, breed inside it and emerge to find the next. When the larvae run out, nematode numbers fall back to nothing.
The whole thing is invisible. You water them in, and over the following two to three weeks the adult population declines because nothing new is hatching.
One genuinely useful caveat: nematodes need a real population to work on. A handful of gnats can be hard to clear this way, because there is not enough prey for the nematodes to establish. For a light infestation, sticky traps and letting the compost surface dry between waterings will do more.
For anything heavier, use both. Yellow sticky traps catch the adults and stop them laying; the nematodes kill the larvae underground. Traps alone leave the larvae eating roots. Nematodes alone leave the adults laying more eggs. Together they break the cycle.
Safe for pets, children and edibles, with no withdrawal period, so microgreens can be harvested the same day. Three coverage sizes. Live product, cannot be returned.