Never fails. Every winter I end up with at least one houseplant home to a small army of tiny black flies. These little black flies that look like a small mosquito are fungus gnats and are quite common in houseplants especially during the winter months. Fungus gnats can infest the potting soil or other planting medium like moss. The flying gnats don’t bite or damage healthy plants, but can be annoying flying around by windows and are seen especially when watering or otherwise disturbing a plant. The larvae of the adult flies feed on plant roots, but usually not healthy ones and rarely cause significant damage to plants.
Fungus gnats thrive in moist conditions where there is decaying plant matter or rotting roots. Minimize the chances of an infestation by cleaning up fallen or trimmed leaves and stems and more importantly, avoiding overwatering and provide good drainage. Too much water and insufficient drainage can cause roots to rot and make your plants an attractive home for fungus gnats.
To kill larvae, allow soil to dry as much as possible between waterings. Of course don’t let it get so dry your plant dies! It is important to water when the plant needs it instead of relying on a set watering schedule. Be sure to empty standing water from saucers too.
Sticky yellow traps can be used to determine which plants have the gnats allowing you to treat those and isolate the affected plants from others that are not affected. Traps will eliminate some flies but are not enough to rid the plant of them.
Indoor plant insecticide sprays such as Bonide’s insecticidal soap, Eight and Neem oil can provide temporary, fast-acting control. Spray the plant and the soil surface where the adult gnats sit. New adults emerge frequently so treat every few days for about two weeks along with the other methods listed above to also kill the larva and end the life cycle. Read the label of the product you using to ensure it is safe to use on the plant you are treating and follow all application instructions. Our helpful staff can direct you to the right products and answer any questions you may have.