Gnats: Do You Have Them?
article was submitted by Mary Jane Frogge, Extension Associate,
University of Nebraska Cooperative Extension in Lancaster County.
The article appeared in the December 1995 NEBLINE Newsletter
and was updated October 1998.
you ever noticed tiny, dark, flying insects in your house, especially
around your houseplants? They may be fungus gnats.
fungus gnats are delicate, gray, dark-gray, or black fly-like
insects about 1/8 inch long. They are often seen running over
the soil surface of houseplants, especially around wet areas.
They also are seen as you water, when they swarm up out of the
plant. Fungus gnats are attracted to light and, in a severe
infestation, will swarm over the windows. Adult fungus gnats
do not damage plant materials but are a nuisance to the homeowner.
The immature fungus gnat lives in the soil and are white, translucent
larvae with shiny black heads. The larvae feed on any organic
matter and can attain a length of about 1/4 inch.
fungus gnats lay up to 300 eggs on the soil surface which hatch
in five to six days. The larvae will feed on any organic matter
present in the soil for 10 to 14 days. The pupal stage occurs
in a silky chamber in the soil. Three to four weeks are necessary
to complete the life cycle of the fungus gnat. Soils containing
large quantities of decaying vegetable matter are most likely
to host fungus gnat larvae. Plants grown in a growing media
containing a high percentage of organic matter such as peat
will have more problems with fungus gnats.
gnat larvae cause damage to the root systems of infested plants
by burrowing in the soil and feeding on the roots and sometimes
the crowns of plants. Seedlings, rooted cuttings and young plants
can be severely damaged or killed by fungus gnat larvae feeding
on root hairs or roots. Fungus gnat larvae infestations on older,
established plants are characterized by little new growth and
foliage that appears to be off color. A severely infested plant
may also drop foliage. While damage from the larvae may not
be extensive for the established plant, the presence of the
adults is considered intolerable.
fungus gnat adults and larvae are discovered on the plant, control
and prevention come in several forms. For infested plants, allow
the soil to thoroughly dry between waterings. This will kill
the larvae through desiccation as well as help prevent future
problems. If the plant is of a type that cannot be allowed to
dry out, drench the soil with an insecticide registered for
this type of use. Be careful to properly measure and apply insecticides
according to label directions for use in a house and take care
to provide adequate ventilation.
best way to prevent new or future infestations of fungus gnats
is to follow proper watering practices for your plants. Houseplants
in the winter normally do not require as much water as at other
times of the year. Fungus gnats are more of a problem in the
winter, most likely due to overwatering. Whenever possible,
allow soil surfaces to dry completely between waterings. A wet
environment is an open invitation to fungus gnats as well as
a host of other problems such as root rot and stem rot.
for more information on Flies, Gnats and