The larva is the most destructive stage in this insect's life cycle. Larvae feed on many kinds of fungi, bacteria and decaying plant material. When in high population, they can stunt and kill young seedlings and rooted cuttings. Gnat larvae have been implicated in the introduction and spread of plant diseases such as Pythium, Verticillium, Scelerotinia and Thelaviopsis. These diseases are all associated with rotting plant tissue.
Adults are harmless, yet a visual nuisance.
Control of fungus-gnats in buildings is simply to locate the soil in which the insects are breeding and dry the soil out. When the soil dries, the larvae die. This procedure could be followed by an occasional spray of aerosol formulations of pyrethrins. Greenhouse control of gnats may be accomplished by maintaining high levels of sanitation in and around structures. Removal of rotting organic matter and reducing the frequency of watering to allow the top layer of potting soil to dry out are positive measures in controlling the pest.