DEALING WITH FUNGUS GNATS.
Adult fungus gnats are about 1/8 inch long and have a delicate appearance. They are frequently seen running across or flying near the soil surface beneath a houseplant. They are poor flyers who are drawn to light.
Although the adults do not feed on houseplants, they can be a nuisance to humans. They are frequently seen in large numbers on nearby windows in severe infestations.
Fungus gnats' whitish larvae (immature forms) have shiny black heads and can grow to be ¼ inches long. The larvae eat decaying organic matter or fungi that grow in the soil. Some species' larvae will eat roots as well.
This feeding is especially harmful to young plants. The first sign of an infestation in older, established plants is a loss of the plant's normal healthy appearance. A heavily infested plant may lose its leaves as a result of larvae feeding on its roots.
Fungus gnats are most common indoors when potting soil rich in organic matter, such as peat moss, is used to grow plants. It is particularly problematic when overwatering occurs.
Healthy Plants tips:
Allow the soil to dry between waterings for plants that can tolerate it (most houseplants, especially in the winter). The larvae will die if the conditions are too dry. Allow no water to stand in the saucer beneath houseplant containers, and invert saucers beneath plants outside to prevent rainwater collection. For control, products containing strains of the biological control agent Bacillus thuringiensis subspecies israelensis can be applied to the soil of houseplants and watered in. To ensure safe use, follow the directions on the label.