Brochures

Indoor Gardening

Fungus Gnats

Fungus gnats are insects that are seen flying around homes and offices. These tiny flies are considered a nuisance and can be rather annoying as they fly around indoors.

Fungus gnat larvae develop in the soil of houseplants and are usually found in the top 5-7.5cm (2-3 inches) of soil, depending on the soil moisture. They feed primarily on fungi, algae and decaying plant material, but will also feed on plant roots and leaves resting on the soils surface. In 2-3 weeks the larvae mature and pupate in the soil and a week later adults emerge. Adults are not very good flyers, and only live for 7-10days. In that time females will lay up to 200 eggs in the soil of plants and the cycle starts again. Female fungus gnats are attracted to moist soil with a high content of peat moss. Houseplants provide an ideal environment for eggs to develop into larvae and then adults.

Fungus gnats seem to be more of a nuisance in the winter. This can be attributed to the decreasing day length and cool temperatures, which slows plant growth and water usage. During the winter, watering practices need to change. Plants require less water so adjusting the frequency of watering becomes necessary. If watering practices are not adjusted, the soil of houseplants will remain moist, which is the perfect condition for fungus gnat development. Also as soil ages and degrades, it holds more moisture which creates the best environment for fungus gnats.

Management

  1. Watering
    Allow soil to dry out between watering's. It is very important to let the top 2.5-5cm (1-2 inch) of the soil to dry out. This will decrease the survival of eggs and larvae plus the dry soil will be less attractive to females looking to lay eggs.
  2. Repotting
    Repotting plants every couple of years is good practice because soil does break down and when it breaks down it tends to hold more moisture.
  3. Maintain Plants
    Remove any decaying leaves, bulbs, roots, or any other plant material. This in turns eliminates a source of food for the fungus gnats.
  4. Chemical Controls
    If after adjusting watering for several weeks and the fungus gnats are still problematic, treatment may be necessary. Because the adults and larvae need different treatments, there are two steps in treatment
    Larvae: Apply an insecticide to the surface of the soil.
    Adults: Place yellow sticky sticks / sticky traps near the edges of the containers, under the canopy of the plant.

Overview:

  • Small insects that are a nuisance, especially noticeable in the winter months
  • Eggs laid in the soil develop into larvae that feed on algae, fungus and decaying plant material
  • Easiest way to control fungus gnats is to allow the soil to dry out between watering's