Fungus Gnats

Fungus gnats (Sciaridae) are small, dark-coloured flies found mainly in plant pots, seed compost and damp growing media. The adults are usually harmless, but their larvae can cause considerable damage to young plants.

The larvae live in the soil and feed on organic matter, fine roots and seedlings. Young plants, cuttings and freshly sown seedlings whose root systems are not yet fully developed are especially at risk.

Typical signs of a fungus gnat infestation include:

small black flies rising from the soil
stunted growth or sudden wilting of young plants
poor germination of sown seed
gnawed or damaged fine roots

Fungus gnats occur especially often where the soil stays constantly moist. Waterlogging, substrates heavily enriched with organic matter and excessive watering all encourage their spread.

To prevent infestation, it is important to let the soil dry out well between waterings and to use structurally stable, high-quality substrates. In cases of heavy infestation, biological measures such as beneficial predators or mechanical barriers can help bring the population under control.