Agricultural Extension Service
The University of Tennessee
SP341C
Insects
Fungus Gnats
Frank A. Hale, Associate Professor
originally developed by Harry E. Williams, Professor Emeritus, and
Jaime Yanes, Jr., former Assistant Professor
Extension Entomology and Plant Pathology
The fungus gnat has recently been recognized as an The larvae or maggots (Fig. B) have shiny black head
important pest in greenhouses. Although greenhouse plants capsules, threadlike white bodies and are up to 1/4 inch long.
are commonly attacked, house plants may also become Larvae feed primarily on fungi and decaying organic matter.
infested. Several genera in the family Sciaridae are of After their normal food supply is exhausted and/or populations
economic concern, such as Sciara, Orfelia, Lycoriella and become very high, larvae may begin to feed on fine root hairs
Bradysia species. or other tender tissues. Chewed roots and underground parts of
the injured stem possess brown scars. Major problems occur
Damage when root rot organisms have begun to damage roots. Fungus
Damage is caused when the larvae, which feed in gnat larvae will then begin to attack the rotting tissues and can
highly organic soils, infest the roots of African violets, greatly increase the amount of damage by their feeding. After
poinsettias, carnations, Easter lilies, geraniums, cyclamens, 14 days, they construct a pupal case made of silk and debris in
bedding plants and foliage plants. Symptoms first appear as the soil.
a loss in plant vigor. As the damage progresses, the plants
may fade, begin to wilt suddenly and finally lose foliage.
Description and Life Cycle A
The adult fungus gnat (Fig. A) is about 1/8 inch long
and is grayish-black. Its slender body with delicate, long
legs and antennae resembles a mosquito. The adult has one
pair of clear wings. In the winter and spring, this insect
becomes most abundant in greenhouses. Fungus gnats
complete development in moist, shady areas in decaying
organic matter, such as leaf litter. The adults, which live for
seven to 10 days, may deposit up to 150 eggs on the moist
B
soil surface or adjacent to the plant stem. Eggs, laid in
strings of three to 40, begin to hatch in four days. Figures A and B. Fungus gnat adult and larvae.
The pupal stage lasts about three days. Adults are weak become infested before being brought indoors. Inspect
fliers and are normally seen running rapidly across the plants carefully, destroying those plants that cannot be
surface of the soil when disturbed. All stages of the life saved. Old plant material and debris in and around the
cycle may be present because of overlapping generations. greenhouse should be removed.
Decoy pots of sprouting grain may be used to attract
Control adult females, which lay their eggs in these pots. After-
Prevention and sanitation are two of the best control wards, decoy pots should be submerged in boiling water
measures. Avoid overwatering, since fungus gnats prefer every two weeks to destroy eggs and maggots.
abundant moisture. Poor drainage and water leaks may also Insecticides may be necessary if populations become
increase populations. Plants should be inspected carefully unmanageable. For effective control, it is necessary to
for signs of infestation before purchase. Sterile potting mix control both the adults and the larvae. Adult fungus gnats
should be used to prevent introduction of fungus gnats. are easily killed with aerosols or sprays. To control larvae,
Houseplants taken outdoors when the weather is warm may soil drenches or coarse sprays should be applied to the soil
surface. Make applications to moist potting media so that at
least the top 2 inches of media are treated.
Control of Adult Fungus Gnats:
● acephate (1300 Orthene TR) — greenhouse
● cyfluthrin (Decathlon 20WP) — greenhouse and interiorscape
(Tempo 20 WP) — interiorscape
● beta-cyfluthrin (Tempo SC Ultra 1 SC) — interiorscape
● permethrin (Astro 36.8 EC) — greenhouse and interiorscape
● resmethrin (Resmethrin EC 26 Insect Spray) — greenhouse and interiorscape
● chlorpyrifos (DuraGuard 20 ME) — greenhouse and interiorscape
● chlorpyrifos plus cyfluthrin (PT Duraplex TR) — greenhouse and commercial garden center
● pyrethrin plus PBO (Pyrenone, Natural Pyrethrin Concentrate) — greenhouse and interiorscape
(1100 Pyrethrum TR) — greenhouse
(PT 1600 X-clude) — hobby greenhouses, homes, interiorscape
● bifenthrin (Talstar 7.9 F, Attain TR) — greenhouse
Control of Fungus Gnat Larvae:
● cryomazine (Citation 75 WP) — greenhouse and interiorscape
● kinoprene (Enstar II) — greenhouse and interiorscape
● fenoxycarb (Precision 25 WP) — greenhouse and interiorscape
● diflubenzuron (Adept 25 WSP) — greenhouse
● pyriproxyfen (PYRIGRO 1.3 ME) — greenhouse and interiorscape
(DISTANCE 0.86 EC) — greenhouse
● Steinernema feltiae, parasitic nematodes (X-GNAT, Nemasys) — greenhouse and interiorscape
● Bacillus thuringiensis subsp. israelensis (Gnatrol) — greenhouse and interiorscape
● azadirachtin (Azatin XL Plus 0.265EC, Ornazin) — greenhouse and interiorscape
Precautionary Statement
To protect people and the environment, pesticides should be used safely. This is everyone’s responsibility, especially the user. Read and follow label
directions carefully before you buy, mix, apply, store or dispose of a pesticide. According to laws regulating pesticides, they must be used only as directed by
the label. Persons who do not obey the law will be subject to penalties.
Disclaimer Statement
Pesticides recommended in this publication were registered for the prescribed uses when printed. Pesticides registrations are continuously reviewed.
Should registration of a recommended pesticide be canceled, it would no longer be recommended by The University of Tennessee.
Use of trade or brand names in this publication is for clarity and information; it does not imply approval of the product to the exclusion of others which
may be of similar, suitable composition, nor does it guarantee or warrant the standard of the product.
SP341C–1M– 3/03(Rev) E12-4615-00-026-03
The Agricultural Extension Service offers its programs to all eligible persons regardless of race, color, age,
national origin, sex, veteran status, religion or disability and is an Equal Opportunity Employer.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
The University of Tennessee Institute of Agriculture, U.S. Department of Agriculture,
and county governments cooperating in furtherance of Acts of May 8 and June 30, 1914.
Agricultural Extension Service
Charles L. Norman, Dean
