How Can I Control Fungus Gnats?

Do you want to control Fungus Gnats using physical and cultural management tactics?

Do you want to control Fungus Gnats using biologic management tactics?

Do you want to control Fungus Gnats using chemical management tactics?

In home situations where fungus gnat adults are a nuisance, it may be possible to reduce the problem by using sticky traps available at retail nurseries and garden centers. Yellow sticky traps can be cut into smaller squares, attached to wooden skewers or sticks, and placed in pots to trap adults. Also, raw potato chunks placed in the soil are very attractive to fungus gnat larvae. These may be used not only to check pots for larvae but also to trap them away from plant roots. After a few days in a pot, remove infested chunks, dispose of them, and replace them with fresh ones.

Three commercially available biological control agents can be purchased to control fungus gnats in pots or container media. These include Steinernema nematodes, Hypoaspis predatory mites, and the biological insecticide Bacillus thuringiensis subspecies israelensis (Bti). Several Bti products are readily available in retail nurseries and garden centers, so these products may be the most convenient for home gardeners to use. Bti does not reproduce or persist indoors, so infestations in potting media might require repeated applications at about five-day intervals to provide control. Nematodes and Hypoaspis mites must be mail-ordered and are live and perishable products, requiring an immediate application.

Insecticides are rarely warranted to control fungus gnats in and around homes. However, if you do apply an insecticide for fungus gnats, consider using Bti or Steinernema feltiae nematodes to control the larvae. If Bti or nematodes aren’t available and high populations are intolerable, pyrethrins or a pyrethroid insecticide may provide temporary, fast-acting control. Spray the surface of potting soil and plant parts where adults typically rest. Do not aerially fog indoors or attempt to spray adult gnats in flight. Read and follow the product's directions.

Because fungus gnats thrive in moist conditions, especially where there is an abundance of decaying vegetation and fungi, avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Clean up standing water, and eliminate any plumbing or irrigation system leaks. Avoid using incompletely-composted organic matter in potting media unless it is pasteurized first. Improve the drainage of the potting mix. Minimize organic debris around buildings and crops. Avoid fertilizing with excessive amounts of manure, blood meal, or similar organic materials.