Fungus Gnats

Question:

I have tiny dark insects that fly out of the soil of my plants. What are they and how can I get rid of them?

Minnesota Master Gardeners say:

 What you are seeing are probably fungus gnats which live outdoors and occasionally come indoors . They are tiny (1/8th inch), fragile grayish to black flies with long, slender legs and thread-like antennae. They thrive in soil that is rich in organic matter and moisture. They are short lived, but can lay up to 200 to 300 eggs during one week. After laying the eggs, the adult winged gnat dies. Legless larvae, which are about 1/4 inch long, clear to creamy-white, hatch in about four days. They feed on the organic matter in the soil and then turn into pupae before becoming adults.

These gnats are only a niuisance, and cause little, if any, damage to houseplants. African violets, geraniums, cyclamens and some bedding plants may be damaged by the gnat larvae feeding on root hairs of these plants when populations are high. The plants will show signs of wilting and loss of vigor. It is possible that gnat damage may weaken the plants and make them susceptible to root rots too.

Fungus gnats are helpful in nature. They decompose decaying organic matter and are important pollinators, as well as being food for small animals including birds, reptiles and beneficial insect predators.

Ways to discourage fungus gnat infestations are:

· Do not overwater your potted plants. Allow the soil to dry between waterings and provide good drainage.

· If plants are summered outdoors, check the soil of plants before taking them back indoors for adult gnats or their larvae.

· Prevent indoor entry of gnats by caulking leaky windows and doors before August, since this is generally the time that they are drawn indoors.

· Place yellow sticky traps on the soil surface to trap the gnats. They can be obtained at a local garden store.

· Place potato slices on the surface of the potting media. The lavae are attracted to it. After four days, remove the potato slices with the larvae.

· Use B.T. i, Bacillus thuringiensis subspecies Israelensis, sometimes called Gnatrol or Knock-out Gnats. It is a natural disease for the fungus gnats which kills the larvae of the gnat. It can be purchased at larger garden stores and from some garden catalogs such as "Gardens Alive".