Fungus Gnat Larvae
Fungus gnat females lay small, yellowish-white eggs on the surface of moist soil. The larvae that hatch are legless, with white or transparent bodies and shiny black heads. Fully grown, larvae measure approximately 1/4 inch in length. They live within soil and eventually develop into pupae. Pupae are initially white, although they darken as they mature.
Some fungus gnat larvae are known for their propensity to feed on the roots and lower stem tissues of plants. These feeding habits stunt and might kill affected plants. Fungus gnats are considered major pests and can cause severe damage to both houseplants and commercial crops. Young plants are highly susceptible to fungus gnat damage. Fungus gnat adults and larvae also are capable of spreading various plant pathogens, which may cause root and crown rot.
Fungus gnat larvae often go unnoticed, as they remain near the roots of affected plants. Adult fungus gnats appear similar to small flies and many times are not identified as being destructive. Symptoms of fungus gnat larvae infestation include bright yellow leaves, slow growth and the presence of small flies, no larger than flecks of pepper, hovering below plants.
Fungus Gnats in Soil
Gnats present in soil are typically the fungus gnats. Because larvae remain within soil and near the bottom of affected plants, fungus gnat infestations are difficult to identify before they have caused considerable damage.
Although fungus gnats may thrive in a variety of areas containing considerable fungal deposits, these gnats most commonly leave their eggs in rich, damp soil. Gnat larvae feed on the roots, root hairs and stems of plants, causing an overall decline in plant health.
The extermination of these gnats generally necessitates the removal of all fungal growth in plant soil. If you have an infestation in potted plants, let the soil dry completely between watering periods. Never overwater houseplants. Commercial crops are more difficult to protect from fungus gnats. If the location of infestation can be identified, topsoil should be raked away to expose eggs and larvae to air and sun. After allowing these damp areas to dry out, specialized chemical treatments may be administered with the assistance of a professional.