Friday, December 18, 2009

Fungus Gnats Hovering Around Plants

Fungus gnats are typically weak fliers, so they usually remain near the potted plant or rest on foliage or growing media. Adult fungus gnats are 1/8 to 1/10 inches in length, grayish black in color, slender bodied with long legs and antennae. They are usually identified by the vein pattern on their wings, with the common species having a Y-shaped wing vein. Female fungus gnats lay tiny, oval eggs in moist, organic debris. The eggs hatch into larvae that are legless, elongate, white to clear in color, with black heads. The larvae eat organic mulch, compost, root hairs, and fungi and can damage roots of plants, causing wilting, poor growth and loss of foliage. Pupation occurs in the soil in silk-like cocoons. The complete lifecycle from egg to adult occurs in about 4 weeks, so continuous reproduction can occur in controlled environments such as homes or greenhouses.

Some Suggestions for Control Measures:

Inspect plants before purchasing and use sterile potting soil.
Allow soil to dry for several days to kill some larvae, since over watering, poor drainage and water leaks can result in a large population of fungus gnats. If the top layer of the soil becomes dry, then the larvae will die and the female fungus gnats will not lay eggs in the soil.

Discard heavily infested plants as to avoid infesting other plants.

Biological Control

Some predators such as Steinernema spp. nematodes and Hypoaspis spp. mites that can be applied to soil to control fungus gnat larvae.

Bacillus thuringiensis israelensis (Bti) can be applied soil to control fungus gnat larvae.

Chemical Control

Larvae can be controlled by many chemicals, including azadirachtin, fenoxycarb and imidacloprid. Adult fungus gnats can be controlled by foliar treatments, including the chemicals horticulture oil, pyrethrins, and bifenthrin.

Picture of fungus gnat. Photo found at Texas A&M University: