Fungus gnats are 2 to 3 mm long and black. The gnats lay their eggs in the soil.
The larvae feed on small fibrous roots of the plants. Cuttings and seedlings are therefore particularly at risk. When the plants have reached a certain size, the damage is minor. The plants are then able to replenish the few roots that have been eaten away very quickly and easily.
Fungus gnats love humus-rich and moist soil. They are very sensitive to drought. They can be controlled very effectively:
- If you keep the soil drier.
- By using yellow stickers. Like all insects, fungus gnats fly to the color yellow. The stickers are coated with glue. The gnats stick to them, and egg-laying is thus prevented. (However, it is difficult to use yellow stickers alone when there is a mass outbreak.
- One biological control option is the use of nematodes (Steinernema), tiny nematodes that feed exclusively on the larvae of fungus gnats. Nematodes are available in garden centers. The packaging unit is 3 million nematodes, enough for 10 square meters of plant area covered with pots. (The nematodes are easily applied with the watering water).