Fungus Gnats

Fungus gnats are small flies that infest soil, potting mix, other container media, and other sources of organic decomposition. Their larvae primarily feed on fungi and organic matter in soil, but also chew roots and can be a problem in potted plants and interior plantscapes. Adult fungus gnats may emerge from houseplants indoors and become a nuisance.

Because fungus gnats thrive in moist conditions, avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Improve the drainage of the potting mix by, for example, increasing the proportion of perlite or sand in the mix. 

In home situations where fungus gnat adults are a nuisance, it may be possible to reduce the problem by using sticky traps. Yellow sticky traps can be cut into smaller squares, attached to wooden skewers or sticks and placed in pots to trap adults. After a few days in a pot, remove infested sticky traps, dispose of them, and replace with fresh ones.

One of the most poplar biological control agents used to control fungus gnats in pots and container media is Mosquito Bits, which is a biological insecticide known as Bacillus thuringiensis subspecies israelensis (Bti). Bti does not reproduce or persist indoors, so infestations in potting media might require repeated applications at about five-day intervals to provide control. 

There are also chemical controls for treatment of fungus gnats. For intolerable infestations, pyrethrins or a pyrethroid insecticide may provide temporary, fast-acting control. Spray the surface of potting soil and plant parts where adults typically rest. Be sure the product is labeled for use on houseplant and indoors.