They hitchhiked their way inside from a patio plant, or perhaps were readily available in your “Deluxe Potting Soil” that was used to repot your philodendron.  These small, flying black gnats are usually more of a nuisance than a threat to plant health.

Their common name “fungus gnat” refers to their feeding on fungi or organic matter in the soil.  The adult gnat lives for about a week, laying up to 200 eggs in moist soil.  Eggs hatch after a few days into larvae, which spends the next few weeks feeding on the fungi.  Larvae develop into pupa, and finally into the winged creature that demands a call to Phelan Gardens for answers.

So how best might we rid ourselves of these pests??  Here are a few suggestions you might consider:

• Small infestations can be detected and controlled using monitor cards which are small, yellow sticky traps that capture the flying adult.

• Allow soil medium to go slightly dry between watering.  Provide a thorough drink for your plants, but allow them to achieve a slight wilt before the next drink.

• Remove the top ½ - 1 inch of soil from containers, and replace with fresh sterile potting soil such as Fertilome Potting Soil.

• For larger infestations, drench the soil with BT (bacillus thurengensis) which is an organic pesticide that destroys the larvae or worm stage.

• Fertilome Systemic Insecticide can also be applied to potting soils to address the larvae stage of this insect—reapplication may be necessary.  Your entire plant will become poisonous for up to six weeks following application .

For any questions you have on this article, or any topic of concern, email us—or better yet, come by and talk to one of our professional staff members.  Remember, Phelan Gardens is open year-round!     

For additional information, check the following links:

• Fungus Gnats, HYG-2114-95
• Fungus Gnats Do You Have Them University of Nebraska Cooperative Extension Lancaster