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Several species of tiny, delicate flies share the common name fungus gnat. Often compared to miniature mosquitoes in appearance, adult fungus gnats don't bite humans or damage plants — but their larvae are a different story. Sometimes referred to as soil maggots, fungus gnat larvae feed on fungi, decaying organic matter and plant roots in soil and potting mixes. They're especially troublesome in greenhouses and on houseplants, where they'll reproduce continually year-round.

Fungus Gnats Identification: Common adult fungus gnats are dark, gray-black flies with gray, transparent wings, long legs and long antennae. Mature size varies, depending on the species, but they're typically less than 1/8 inch long. Their translucent, wormlike larvae have distinctive black heads and grow up to 1/4 inch long.

Signs/Damage of Fungus Gnats: The first clue to a fungus gnat infestation is often a swarm of adult gnats around freshly watered container plants. In landscapes, adult fungus gnats are frequently found near decaying organic matter such as grass clippings, leaf debris or compost. Fungus gnat larvae typically stay hidden in the top 2 to 3 inches of soil, but affected plants show signs of wilting or stunted growth. Root damage caused by the larvae encourages root rot, which intensifies larval root feeding and leads to rapid decline of the plants.

How to Control Fungus Gnats: Effective fungus gnat control targets soil surfaces and vegetation to treat existing gnats and new adults as they mature and emerge. For container and landscape treatments, spray to cover all surfaces thoroughly. Always take houseplants outdoors for treatment and allow them to dry before they come back inside. GardenTech® brand offers several highly effective products to kill fungus gnats by contact and keep protecting for up to three months:

  • Sevin® Insect Killer Concentrate provides an economical alternative for extensive outdoor coverage with a pump-style sprayer. Use the convenient measuring cap to measure the concentrate into the sprayer. Then add water and mix well. This product treats lawns, gardens and areas around your home.
  • Sevin® Insect Killer Ready to Spray, attached to a regular garden hose, automatically mixes and measures as you spray. Cover all plant and soil surfaces thoroughly to reach existing fungus gnats and protect against future generations.

Tip: Fungus gnats are poor fliers that rarely go far from the plants they inhabit. They're most active when soil is moist. Water plants right before treatment to stir up gnats and optimize results.

Always read product labels and follow the instructions carefully, including pre-harvest intervals for edible crops.

GardenTech is a registered trademark of Gulfstream Home and Garden, Inc.

Sevin is a registered trademark of Tessenderlo Kerley, Inc.

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