Fungus Gnat Control

With so many new indoor plant enthusiasts building their own collections, it is important to address a common unwanted addition that sometimes comes home with new plants -bugs! Insects are easily brought home with new acquisitions. Always separate a new plant from the rest of your collection, at least across the room from other plants, if not in a separate room, for the first two weeks. This allows you time to observe the new plant daily. Look closely for sap, bumps, pits, white fluff, cast-off dried skins, or actual insects crawling across soil or flying when disturbed. The most common pests seen on indoor plants include spider mites, scale, mealy bug, aphids and fungus gnats. The problem that generates the most calls for help from individuals is fungus gnat infestation.
To verify you have fungus gnats, observe the soil surface for anything moving, brush the soil surface with your fingers and slightly shake the plant to see if anything flies up. Fungus gnats lay eggs in the top layer of soil, then hatch into larvae, which then become pupa, before becoming flying adults.
Wetting of the soil is the impetus for the insect to evolve to the next life stage, so new adults are usually seen a few minutes to a few hours after watering. Gnat larvae do feed on plant roots and provide entry for pathogens, including those that cause root rot. Sanitation is key.
Remove the top inch or two of soil, depending on pot size, and replace with fresh, commercially prepared soil suitable for the species. Wash out trays and saucers with soap and water, and try to keep soil surface on the drier side. Frequent light watering encourages gnats. Yellow sticky cards help control adults by keeping them from reproducing and may allow you to identify the species. Bacillus thuringensis (Bt) treatment is very useful. Nematodes and Hypoaspis mites can also be used. Some success can also be found in adding a couple of drops of ivory soap to the water before wetting soil. We use a Bt treatment in all our indoor plants each spring in March, about the time that overwintering eggs often have developed through larvae and pupa and move to the adult stage.
If you suspect gnats, identify and confirm as soon as possible and take action. Letting them reproduce may lead to clouds of adults disturbing you and your family and attacking your plants for weeks to come.