Have you ever noticed tiny, dark, flying insects in your house, especially around your houseplants? They may be fungus gnats. (Fungus gnats look dark gray in color.) These small, non-biting flies are completely harmless to humans, except for the annoyance of their presence.
To plants, however, Fungus gnat larvae cause damage to the root systems of infested plants by burrowing in the soil and feeding on the roots and sometimes the crowns of plants. Seedlings, rooted cuttings and young plants can be severely damaged or killed by fungus gnat larvae feeding on root hairs or roots.
When houseplants are infested it may mean they are overwatered.
Get Rid of Fungus Gnats - Solution 1
Fungus gnats do not survive if the soil becomes dry, so one management option is to permit the soil to dry out between waterings. Remember though, you don’t want to let the soil get so dry that you are stressing the plant, your goal is simply to not have soggy, wet soil all the time.
Solution 2: Knock-Out Gnats
This strain of Bacillus thuringiensis (Bt/H-14), is an organic insecticidal bacterium, which provides very effective fungus gnat control for houseplant growers and home greenhouses.
Populations of fungus gnats (often thought of as “fruit flies”) usually peak during winter and spring. The adult insects are tiny and hard to control. They like to lay their eggs in peat moss, humus-rich organic soil and potting mediums.
Infested plants wilt, roots rot and the plants may eventually die. But when roots are drenched with Knock-Out Gnats, the larvae ingest the larvicide and die.
Use as a soil drench, 2-8 teaspoons per gallon of water. Make 3 weekly applications to control successive generations of larvae. You can monitor effectiveness of Knock-Out Gnats with sticky traps.