What are fungus gnats?
Fungus gnats (right) are small (~1/8"), dark, primitive* flies that often plague potted houseplants, interior plantscapes, greenhouses, and commercial mushroom growers. Fungus gnat larvae live in soil where they feed on soil fungi and plant roots. Full grown fungus gnat larvae are about 1/4" long and have a very distinct, dark head capsule (lower right).
Fungus gnat larvae damage plant roots
Adult flies can be a nuisance when present in high numbers but the damaging stage is the larvae that feed on plant roots. Fungus gnat larvae can do significant damage to young plants that don't yet have a developed root system. They are most often a problem in greenhouses and potted house plants.
Fungus gnats may have many generations per year so populations can build quickly under favorable, warm conditions. The best, and safest, way to mange fungus gnat damage is to monitor for adult flies using yellow-colored sticky traps and if an infestation is found you can treat soil with entomopathogenic nematodes (see below for details).
* Primitive flies include gnats, midges and mosquitoes. These are generally small (except crane flies), delicate flies with long antennae. The "higher" flies, like house flies, have short antennae and tend to be larger and more robust.
