PK-F05 · Flies and gnats
How to get rid of Fungus gnats
Sciaridae / Mycetophilidae (sciarid types in pots)
Need a look-alike split? Use Fruit fly vs fungus gnat vs drain fly, then follow the control sequence on this page.
Fungus gnats run on wet houseplant soil. Let the surface dry, empty saucer lakes, and use yellow sticky cards as monitors. Treat larvae in the mix only with products labeled for ornamental soil, such as Bti drenches. Calendar watering is how you farm them.
Sciarid fungus gnats are weak fliers around pots, not a cloud over a fruit bowl. Larvae live in the top inch of wet mix: translucent bodies with black heads, feeding on fungi and fine roots. Nursery plants and decorative pots without drainage move them indoors. If adults hover on bananas or beer, that is a fruit fly job instead.
How to identify Fungus gnat
- Tiny, long-legged, Y-shaped wing vein (sciarids), run across soil.
- Larvae in the top inch of wet mix, translucent with black heads.
Signs of an infestation
- Clouds when you water.
- Adults on nearby windows.
- Wilting from root feeding in heavy cases.
Biology and why they show up
Greenhouse and indoor plant pests. Wet peat is a gift. They can vector some plant pathogens in production greenhouses.
Health and property risk
Plant damage, nuisance. Not a human biter.
Proven control sequence
Work in this order. Skipping inspection or exclusion is why most “treatments” bounce back in a week.
- Let the soil surface dry. Water when the mix needs it, not on a calendar. Improve drainage. Dump standing water in saucers. Wet peat is a gift to sciarids.
- Yellow sticky cards as monitors. Cards at soil level tell you if dry-down is working. They knock down some adults; they do not finish the job if the pot stays soggy.
- Treat larvae only if labeled. Bti (Bacillus thuringiensis israelensis) products labeled for gnats in soil. Do not dump random insecticides into a pot in a child’s room. Kitchen foggers contaminate food and miss the pot.
- Repot mix that never dries. If the mix is decomposed, compacted, and never dries, repot into a drainable mix. Inspect nursery plants before they enter. Decorative pots without drainage are a factory. Compare look-alikes in Fruit fly vs fungus gnat vs drain fly.
Matching tools for these steps can be bought on Amazon. Buy the field kit.
Tools for fungus gnats in potting soil
Dry the mix. Sticky cards show whether the next watering still hatches a cloud.
As an Amazon Associate, Pest Kill earns from qualifying purchases. The EPA label is the law for any pesticide. These links match the sequence on this page — they are not a shopping list instead of identification. Details: advertising disclosure. Browse the full tools catalog.
Hardware
Yellow sticky insect cards
Cards census fungus gnats and some greenhouse flyers. Let potting soil dry between waterings or the card is a scoreboard. Keep the sticky face off pets and children.
Prevention that actually sticks
- Do not start plants in chronically soggy decorative pots without drainage.
- Inspect nursery plants before they enter.
When to hire a licensed professional
Commercial greenhouses. Homes: usually culture change.
United States and Tier 1 notes
Any indoor plant culture globally.
Common questions
Will cinnamon on soil kill them?
No. Cinnamon on potting mix is not a reliable control program. Let the surface dry, empty saucer lakes, and use a labeled Bti drench only if larvae remain.
How do I get rid of fungus gnats?
Dry the soil surface, use sticky cards, and treat larvae in the mix only if labeled. Repot mix that never dries.
What do fungus gnats eat?
Larvae eat fungi and fine roots in wet media. Adults are weak fliers around the pot, not hovering on bananas.