Home gardeners often find little white bugs in the soil of potted plants. These insects are the larval form of fungus gnats, which are non-biting insects that resemble mosquitoes. Fungus gnats are known to infest damp soil, algae and decaying vegetable matter. While fungus gnats are relatively harmless, they can become a nuisance when they infest indoor plants.
Adult fungus gnats are also known as dark-winged fungus gnats that measure 1/8 inch in length. Female fungus gnats lay their eggs in the potting soil which hatch in 5 to 7 days and produce white maggot-like larvae. Fungus gnat larvae have black heads and measure 1/4 inch in length. The larvae remain two or three inches beneath the soil surface and pupate within 8 to 20 days to become adult fungus gnats.
Fungus gnat larvae feed on matter found in potting soil and on plant roots. This feeding can damage the root system of the plant and cause plants to appear unhealthy. Small plants and young seedlings typically sustain the most severe damage from fungus gnat larvae. Root damage can increase the risk of root diseases. Adult fungus gnats are drawn to light and are often found flying in windows. These gnats are a nuisance as they swarm any time plants are moved or bumped.
Using sterile potting soil in your houseplants will eliminate fungus gnat development. Repotting plants every few months will also reduce infestations. Fungus gnats are most abundant in saturated soil, so avoid over-watering your houseplants to reduce infestations. Allow the potting soil to dry completely before providing your plant with additional water. Fungus gnats are also abundant in wet areas inside the home such as slow drains and areas of standing water. Cleaning your drains with a stiff brush can eliminate fungus gnats.
Adult fungus gnats can be eliminated by spraying them with aerosol sprays labelled for use on flying insects. Apply these sprays to the soil of infested houseplants and around the rim of the pot to control fungus gnat larvae. Yellow sticky traps attract adult fungus gnats and capture them. Place these traps in window sills or near infested plants for best results.