I have fungus gnats everywhere. Can you help?

I grew several plants outside this last summer Rosemary, Geranium, etc. When I brought them in for winter it seems I now have fungus gnats in all my houseplants. Please give advice. I would prefer not to use chemicals but am getting desperate.

Winter is a time that a lot of indoor plants become infested with fungus gnats, due to excessive soil moisture.

How to control fungus gnats

Avoid over-watering houseplants. I suggest that you check the soil before watering to make sure the top inch is dry. The larvae of the fungus gnats live in the top half inch or so of moist soil, so letting the planting medium dry out lessens the chance of infestation.
Use yellow sticky traps. This is not a biological control, but it will reduce the population of adult gnats.
Use Bacillus Thurengiensis Israeli (BTI). Use BTI as a drench to kill the larvae.

For additional information, check out this article for more alternatives: Fungus Gnats, University of California IPM

Want to learn more about this topic? Explore more resources from OSU Extension: Healthy homes, Insects

Was this page helpful?

Related Content from OSU Extension

Comparing the effectiveness of pesticides in controlling thrips in dry bulb onions

Onion growers in Treasure Valley have faced difficulties in controlling thrips. One of the problems is resistance to commonly used insecticides. Researchers conducted tests to find the most effective insecticides.

Lynn Jensen | Jul 2010 | Article Peer reviewed (Gray level)

OSU educates growers about invasive, fruit-damaging fly

Continuing study is leading to targeted approaches that allow producers to bring crops to market while reducing pesticide use

Vaughn Walton | Jun 2021 | Impact story

Critter corner

A collection of information relating to the critters we find in our gardens, from flies to wireworms.

Jul 2018 | Collection

Bugs in my pantry—what do I do?

Two weeks ago, when fixing brown basmati rice for dinner, I noticed many small, black bugs. Some were dead, but many were still crawling actively. I purchased this rice two months ago, but I threw all of it away. Today ...

Jeanne Brandt | Apr 2016 | Featured question

Don’t worry, maggots help break down compost pile

Soldier fly larvae are voracious consumers of high nitrogen materials such as kitchen food scraps and manures, as they decay.

Kym Pokorny | Aug 19, 2022 | News story

No room for vegetables? Pot up your plants

There are some dwarf and miniature varieties of vegetables, such as Thumbelina carrots or other baby vegetables that work particularly well in small confines.

Kym Pokorny | Mar 26, 2021 | News story

Northern giant hornet still far from Oregon

The invasive hornet is a concern and residents are encouraged to keep an eye out for the hornet and report possible sightings.

Kym Pokorny | Mar 10, 2021 | News story

What's the buzz in school gardens? Part 1

Join us as for a fascinating interview with one of the world’s foremost authorities on bees and pollination - Andony Melanthopoulos with Oregon State University. We're talking about how bees fit into the world of school gardens! This is part one of a two-part series.

Michelle Markesteyn, PhD, MSEL, Rick Sherman | Jun 2024 | Podcast episode Peer reviewed (Gray level)

How to Manage Your Forest - Module 2: Management Practices

Learn practical, research-based skills and techniques covering a wide array of valuable forest management topics that will help you achieve your goals and objectives.

Bob Parker, Steve Bowers, Tristan Huff, Stephen Fitzgerald, Paul Adams, Paul Oester, Dave Shaw, Fran Cafferata Coe, Julie Woodward, Nicole Strong | May 2018 | Video Peer reviewed (Gray level)

How to Manage Your Forest - Module 1: Silviculture

Our first online training module covers Silviculture, or the art and science of managing forests to achieve your objectives, with nine sections to view.

Glenn Ahrens, Bob Parker, Paul Oester, Stephen Fitzgerald | May 2018 | Video Peer reviewed (Gray level)

Scouting and collecting Wheat Head Armyworms

What growers can do to scout for and help identify wheathead armyworms.

Mary Corp | Oct 2008 | Article

Russian Wheat Aphid

What your rolled-up wheat leaves mean.

Mary Corp | Oct 2011 | Article

New OSU volunteer program tackles statewide native bee inventory

The Master Melittologist program intensively trains volunteers on the meticulous work of locating and cataloging the bees that no one has seen before.

Kym Pokorny | Dec 18, 2020 | News story

Tackling Potato Virus Y

Oregon State University research on Potato Virus Y in potato production in the Pacific Northwest and worldwide uses biotechnology tools like CRISPR to study genes associated with the defenses of potato to the virus.

Aymeric Goyer, Max Combest | Oct 2019 | Video Peer reviewed (Gray level)

Vegetarians, Predators and Parasitoids: Lesser-Known Wasps of Oregon

Wasps are more diverse and ecologically important than most people realize. Learn about the fascinating world of lesser-known wasps.

Tucker D. Hoffman, Scott R. Mitchell, Sandy DeBano, Christopher Adams, David Wooster | May 2024 | Extension Catalog publication Peer reviewed (Orange level)

Integrating Integrated Pest Management

Insects, weeds and plant pathogens are problems that confront farmers in trying to grow a successful crop. Insect pests can defoliate crop plants. Weeds can outcompete crops for light, water and nutrients. Pathogens can cause disease epidemics that destroy entire crops.

Silvia I. Rondon, Mary Corp, Stephen M. Van Vleet, Stuart Reitz, Pamela Hutchinson | Jul 2015 | Video

Pest Scene Investigator: A Training Curriculum

This curriculum is a resource for Extension foresters, educators, natural resource professionals, landowners, and others wishing to increase their ability to assess and mitigate forest health situations. This curriculum ...

Nicole Strong, Paul T. Oester, David C. Shaw, Brandy Saffell, Tiffany Hopkins, Carrie Berger | Mar 2017 | Extension Catalog publication Peer reviewed (Orange level)

Ivy removal in a home landscape

Linda McMahan tackles ivy and shows how you can remove it from trees and fences.

Linda R. McMahan | Sep 2008 | Article Peer reviewed (Gray level)

Have a question? Ask Extension!

Ask Extension is a way for you to get answers from the Oregon State University Extension Service. We have experts in family and health, community development, food and agriculture, coastal issues, forestry, programs for young people, and gardening.

Ask us a question