Insects in Potting Soil

Fungus gnats are insects that fly across potting soil surfaces.

Indoor plants add texture and create warmth to any indoor atmosphere. Insects often thrive on the damp, rich soil of indoor plants, making them a nuisance. Fungus gnats are the most common potting soil insect of indoor plants.

Identification

Fungus gnats measure 1/8 to 1/10 inch and are long, black insects that resemble mosquitoes. These insects have one pair of wings and lay eggs in potting soil. The larvae of fungus gnats are thread-like maggots that measure up to 1/4 inch.

Effects

Fungus gnat larvae feed on potting soil that is rich in organic matter and often causes injury to the potted plant's roots. Brown scars often appear on the roots of plants, and roots often look chewed. Fungus gnats often damage indoor plants, greenhouse plants and flower beds.

Control

Use sterile potting soil to prevent fungus gnat infestation. Avoid overwatering your plant and provide adequate drainage to prevent fungus gnats. If you take houseplants outside, inspect them carefully for soil insects before bringing them indoors. Adult fungus gnats are controlled by spraying insecticides labeled for flying insects.

References

• Colorado State University: Managing Houseplant Pests
• Ohio State University: Fungus Gnats