How to Control Fungus Gnats on Indoor Plants

Fungus gnats are those little hopping bugs you see when you water your indoor plants. They are 1/32 to 1/50 inches with black or gray bodies and clear wings. Plants grown under cover are most susceptible. The larvae feed on dead roots and leaves, but sometimes consume tender new roots.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Pyrethrin
• Sticky Traps
• Bt

1. Look for small insects on the surface of the soil. They will be active when you water or move the plant. The larvae are 1/4 inch white-bodied maggots with black heads and can be found just under the surface of the soil.

2. Keep plants clean of fallen leaves and debris. Fungus gnats feed on dead plant material.

3. Plant pots of wheat to lure fungus gnats, then compost the soil and the wheat once the female fungus gnats have laid their eggs in the pots. This technique works well in greenhouses or greenhouse windows.

4. Use yellow sticky traps placed near the infested plant to catch adult fungus gnats.

5. Water with a solution of Bacillus thuringiensis, an organic control for caterpillars, to kill insect larvae. Bacillus thuringiensis (or Bt) is a bacteria and is safe to use around children and pets.

6. Drench the soil with a solution of pyrethrin, an organic pesticide made from chrysanthemums.

Tips & Warnings

• The adults cause no damage to healthy, mature plants but are a nuisance inside the house.
• You can make your own sticky traps by spreading tanglefoot onto stiff yellow paper.
• Always try the least toxic method of pest control as your first step.
• Although Bt is organic and safe to use, it will kill all types of caterpillars, including butterfly larvae. Spray only the plants that are affected.
• Never use chemical pesticides inside the house.

[killfungusgnats]

on 4/14/2009 I read this suggestion elsewhere online, and it works wonders at catching the adult flies, but not at eliminating the problem at its source: Put out bowls of yellow, soapy water (or yellow bowls of soapy water). You can use a drop or two of food coloring and dish soap. For some reason, the flies LOVE this, fly in, and get stuck. I put them by problem plants, by lamps (they like yellow light, too) and in sunny parts of the house. I think their attraction to yellow also explains why they end up in cups of coffee or tea. They are definitely not attracted by fruit fly traps (vinegar, fruit, etc.).Unfortunately, I have tried the Bt, and it is not working. I'm moving onto pyrethin, and we'll see how that goes.ALSO, I have found the larvae repeatedly crawling around the kitchen sink. We've bleached that area, and are doing our best to keep the sink clean and dry to prevent that from being a bre

[roslyn1976]

on 3/26/2009 can fungus gnats live in areas without plant matter? I have been fighting this infestation for months, and they seem to be moving into areas in the house with out plants. I am wondering if they are living in the carpet in our bathroom? (i know, its comming out this summer, stupid contractors trying to save some bucks).

[greenmum]

on 2/3/2009 The apple cider vinegar didn't work for me, either. However, they did seem to like the coffee I accidentally left down in my seeding area. For anyone who's interested, it was with cream and sugar. Have no idea if that had any bearing on it at all.

[Maimee]

on 7/30/2008 ok, so i really don't want to spend a lot of money getting rid of these stupid gnats. Can i just let them dry out outside for a bit? What does the sand do? What does the soap do?

[Lithorne]

on 7/1/2008 Using the dirty water that comes out the bottom after watering seems to work just as well as vinegar and smells much less. Be sure to add a drop of unscented soap to lower the surface tension. I'd say to avoid pyrethrin, since it's no more effective than Bt and much more toxic. The best measure I've found is to put sand on the soil surface, somewhere between 1/2 to 1 inch thick. Using all three measures at once gives the best control.