Fungus Gnats in Your Indoor Houseplants

Fungus Gnats can become a problem on potted house plants, especially during the holiday season because we are bringing in flowering plants from nurseries, and big box stores, as well as receiving them as gifts. They are difficult to control because of their tiny size and life cycle.

Here are some effective ways to treat them:

Proper Watering
Let the potting soil dry out between watering. The dry surface is less attractive to females depositing eggs, and if eggs are deposited, they fail to hatch because of lack of moisture. This cultural approach can be very effective.

Fly Tape or Sticky Traps 
The gnats are drawn to the yellow color. No need to fall for the trap of buying anything with pheromones either. Simply a yellow sticky trap.

Biological Control
Bt is available (Sold under the names Gnatrol, Mosquito Bits) is very effective in controlling the larvae, is not harmful to beneficial insects, and is approved for organic growers. Plus, it is so easy to use! Just sprinkle it on the soil in the pot!  Nematodes are also a natural option.

In severe infestations, you may consider washing the roots and re-potting your plant in fresh soil, or simply spraying a light application of indoor houseplant insecticide. When you use any insecticide, be sure to read and follow all label instructions! Finish by creating a tent over your plant and secure the bottom with a rubber band. Watch for a couple of weeks to see if there is still activity.  Don't worry about watering because you have created a little greenhouse but keep the plastic from touching the leaves. 

Contact your local University of Idaho Extension office for more information on controlling fungus gnats in your home.