The Purdue Plant and Pest Diagnostic Laboratory

Fungus Gnats

The following questions were sent to the P&PDL diagnosticians here at Purdue University:

Question 1: I have noticed little black flies around my houseplants. What are they?

Question 2: How do I safely dispose of gnats that are apparently living in the dirt of my house plants? I'm really concerned about what type of agent I should use due to our family's newborn.

Question 3: I have browsed your site trying to find out what my household pest is. I have what looks to be "fruitflies" in my houseplants, the only thing that I could find that came close was "Fungus Gnats", is this commonly what I have? I would have thought they were beneficial because I assume they are thriving on dead plant material, but I have my doubts. Do Fungus Gnats look like fruitflies?

Question 4: I was viewing your site and thought you might be able to help me. My wife and I have about 10 plants in our kitchen. We have recently had a problem with tiny flies which look almost like fruit flies. They have invaded the plants and are driving me crazy. I tried a chemical bug spray. That worked for a while but they just came back, and the spray stunk up the kitchen for a week. I also tried misting them with a soap and water solution but they will not go away. I hate to throw all of them out. Can you help. Any tips would be greatly appreciated.

Answer: It sounds like you are describing fungus gnats. Fungus gnats are common pests in greenhouses and homes throughout the U.S. Larvae of fungus gnats (maggots) are white with shiny black heads and are approximately 1/4 inch in length. Adults are black or brown in color, slender, and 1/8 inch in length. They have one pair of delicate, clear wings and have long, slender antennae. The adults are often confused with mosquitoes because of their long, slender dangling legs. Females can lay up to 200 small whitish eggs in the soil. Upon hatching, larvae will begin to feed immediately on the roots of plants. As soon as the larvae are mature, they pupate in the soil. In about four to seven days, the adults emerge and will live about one week. Larvae have the ability to damage plants by feeding on roots and root hairs. Seedlings and young plants are extremely vulnerable to this feeding. The larvae also have the ability to bore into stems, interrupting nutrient and water flow, which decreases the plant's health and vigor. Adults and larvae are both capable of transmitting fungal pathogens.

Proper sanitation and chemical applications are the most common measures that can be taken to control fungus gnats. For additional information on fungus gnat control, refer to publication E-111, Fungus Gnats and Shore Flies (173K/PDF), which is available at your local Cooperative Extension Service office.

--Corey Gerber


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