Gnats and Potting Soil

Fungus gnat larvae infest moist potting soil.

You examine new plants before buying them to make sure they are healthy and will thrive in your home. It is just as important to examine potting soil before purchasing it -- and again before using it in your home -- to avoid the risk of a fungus gnat infestation.

Fungus Gnats

Moist potting soil that is left unsealed and outside can attract fungus gnats, especially if the potting soilcontains high amounts of organic matter. Fungus gnat larvae live inside potting soil, while the flying adults can move throughout your home, according to the University of Massachusetts Extension.

Issues

Fungus gnat larvae usually feed on fungal matter found in potting soil. They thrive in moist conditions, especially if soil is over watered. They can also feed on the roots of healthy plants. If enough larvae are active, they can damage the plant's tissue, injuring a bulb or a growing seedling. In severe cases, they can kill a plant.

Solutions

Always examine potting soil for gnats and larvae before bringing it into your home. If you do have fungus gnats, you can treat your potting soil with insecticides like diflubenzuron that are designed to kill the larvae. Others, like permethrin, will kill the adult gnats. You could need to apply the insecticide more than once to completely clear the infestation.

References

• University of Massachusetts Extension: Fungus Gnats