Fungus gnats are small, short-lived gnats that infest soil, and other media, and sources of organic decomposition. They affect plants mainly by their larvae, which attach to the roots of plants and drain them of nutrients causing significant damage.

Fungus gnats

Fungus gnats are a common pest of plants grown indoors especially where humidity and moisture are high and usually first noticed when the harmless adults are seen flying around. Adult fungus gnats are similar in appearance to mosquitoes as small to tiny flies with long legs, long thin clear wings, and segmented antennae that are longer than their head. Fungus gnats infest soil, potting mix, other container media, and other sources of organic decomposition. The adults, despite being a flying nuisance, are harmless to plants. it's the larvae that are most damaging to seedlings, cuttings, and young plants by feeding on fungi and organic matter in the soil, they also eat roots damaging the tender plant's root hairs

Fungus gnat eggs are bearly visible, oval, smooth, shiny white, and semi-transparent, but the larvae or maggots are legless having a shiny black head and an elongated body up to 1/4 inch long. Pupae occur in silk-like cocoons in the soil. While the adults are poor fliers and tend to get disturbed by watering. After hatching, fungus gnat larvae promptly begin feeding. Their feeding can cause significant root damage and severely inhibit nutrient uptake. The resulting damage commonly shows up as nutrient and/or water deficiency brought upon the plants by decreased root absorption.

Plant symptoms that indicate fungal gnat infestations are sudden wilting, loss of vigor, poor growth, yellowing (chlorosis), and even foliage loss. With severe infestations, a considerable portion of the plants may be lost. Most of the fungus gnat’s life is spent as a larva and pupa in organic matter or soil, so the most effective control methods target these immature stages rather than attempting to directly control the more mobile, short-lived adults