Order Diptera, family Mycetophilidae, Sciara spp.
Adult--1/10" to 1/8"
Black, brown, or dull yellow, mosquito-like flies. Some are more brightly colored. Humped thorax and long legs.
Adults lay eggs that hatch into slender, cylindrical larvae that eat fungi in decaying organic matter. The larvae of some species eat small insects, worms, and plant roots. Adults live about one week and lay up to 200 eggs that hatch in about four days. Complete metamorphosis.
Habitat includes grain plants, cucumbers, potted plants, and bonsai plants. Commonly found in moist wooded areas but also in indoor house plants. Often troublesome in indoor atriums.
Larvae eat fungal matter and decaying organic matter. They will also do some damage to plant roots and stems.
Can damage plant roots but are more of an irritation than anything.
Control: Bacillus thuringiensis 'Israelensis,' Predatory mites (Hypoaspis miles), Beauveria bassiana and parasitic nematodes (Steinernema feltiae). Water potted plants and courtyards less often. Neem or citrus oil products. A drench of citrus, compost tea, and molasses works as well as anything.
Drench into the soil with a neem product such as Azasol and allow soil to dry out between waterings. Bti products work also but not as well as the neem drench.
Mulching potted plants, just as you would outdoor beds, helps with pest control. Add lava sand and earthworm castings and cover these materials with aged pecan shells or cedar flakes. Adding a tablespoon of natural apple cider vinegar to each gallon of irrigation water will also help keep plants healthy and control pests like fungus gnats.
Small nuisance insects that start out in the soil of potted plants. Drench into the soil with neem products and allow soil to dry out between waterings. Bti products work also but not as well as the neem drench. Cornmeal in the soil will also help.
A listener reported this idea. Put apple juice or apple cider in a mason jar, cover the opening with plastic and secure with a rubber band. Stab a small hole in the plastic. The small gnats are attracted the apple juice, enter the small hole and can't get out.