Tiny Yellow Eggs & Mold on Indoor Plants

Ideal Conditions

• Fungus gnat adults seek out moist soil to lay their eggs. The larva eat decaying organic matter and require a very wet environment to survive to adulthood. Because of this, fungus gnat infestations often occur in houseplants that have been overwatered and are growing mold or mildew on the surface of their soil.

Fungus Gnats

• Fungus gnats are very small flies, described as looking similar to mosquitoes or fruit flies. There are several species of various sizes, but most are not more than 1/8 inch long as adults. They are not very strong fliers and are generally only seen on and around host plants. Adults live for only a few days to a week. Because of this, fungus gnat populations can get out of control quickly.

Larval Damage

• Larvae are the most serious danger from fungus gnats. The adult insects feed mostly on rotting organic material, but larvae are sometimes found feeding on plant root hairs, roots or even the crown of plants. They are indiscriminate feeders and do not have a preference among plants, except for their attraction to high-moisture environments. Infestations are often followed by a general lack of vigor and wilting of the plant.

Fungus Gnat Removal

• Fungus gnat larvae can be difficult to eliminate without a soil change. If possible, remove the plant and growing medium from the pot, clean the pot thoroughly with bleach and replace the medium. Rinse the plant's root system well before placing it in the new soil. If a soil change isn't possible, such as with a large potted tree, soak the soil with a solution containing Bacillus thuringiensis or neem. Check the soil before watering the plant going forward. Most plants don't need wet soil; some even thrive if allowed to dry between waterings.