Fungus gnat larvae cause damage to the root systems of infested plants by burrowing in the soil and feeding on the roots and sometimes the crowns of plants. Seedlings, rooted cuttings and young plants can be severely damaged or killed by fungus gnat larvae feeding on root hairs or roots. Fungus gnat larvae infestations on older, established plants are characterized by little new growth and foliage that appears to be off color. A severely infested plant may also drop foliage. While damage from the larvae may not be extensive for the established plant, the presence of the adults is considered intolerable.