Both the larval and adult stages of this small plant pest can spread disease problems in home gardens. Here’s how to get rid of fungus gnats indoors.
A common pest of indoor gardens, including greenhouses and interiorscapes, fungus gnats (families Mycetophilidae and Sciaridae) are most often seen flying at windows and around house plants. While adult gnats occasionally become a nuisance, the larval stage can damage tender plant roots with their feeding. Plant symptoms appear as sudden wilting, loss of vigor, poor growth, yellowing and with severe infestations, a considerable portion of the plants may be lost. Plants such as geraniums, African violets, carnations and poinsettias are especially prone to injury. They are most damaging to seedlings, cuttings and young plants.
Adults are delicate, grayish black, mosquito-like flies (1/8 inch long) with long legs and one pair of clear wings. They are not strong fliers and emerge from potted plants, especially when watering. Larvae or maggots (1/4 inch) have a shiny black head and an elongated, whitish to transparent body. They are most abundant in damp, rich soils and feed on root hairs, fungi and other organic materials.
Adults live about one week and lay up to 300 eggs in rich, moist soils. Within 4-6 days tiny larvae emerge and begin feeding on plant roots during their two week period. The pupal stage lasts 3-4 days before young adults leave the soil and begin the next generation. The entire life cycle from egg to adult may be completed in as little as 3-4 weeks depending on temperature. Indoor potted plants host many overlapping generations per year.
Fungus Gnat Control
Inspect plants thoroughly prior to purchase for signs of insect pests. Fungus gnats do best in damp soils; be careful not to overwater, especially during winter months when plants use less. If pests are present, allow the soil to dry out between waterings. This will limit the larval damage and help prevent further problems. Yellow sticky traps placed horizontally at the soil surface will capture a large number of egg laying adults. Mosquito Bits (Bacillus thuringiensis var. israelensis) contain a highly selective, biological larvicide for use in greenhouses. It may be used on a wide variety of ornamentals, as well as all bulb crops, bedding plants and vegetable sets. Top dress houseplants with beneficial nematodes to destroy the larvae stage. Flying Insect Killer is a non-toxic spray that will get rid of gnats and other insects that gather around windows.
Tip: The fungus gnat predator (Hypoaspis aculeifer) will actively search for fungus gnat larvae and other harmful soil insects to attack after release. This beneficial insect will attack the larvae and feed on their contents. Release 10,000 predators per 200 – 1,000 square feet depending on pest levels.