pnfungusgnats

Statewide Integrated Pest Management Program August 2013

P EST N OTES Publication 7448

Integrated Pest Management in the Home, Garden and Landscape

F ungus g nats

Fungus gnats are small flies that in -

fest soil, potting mix, other container

media, and other sources of organic

decomposition. Their larvae primarily

feed on fungi and organic matter in

soil, but also chew roots and can be

a problem in greenhouses, nurseries,

potted plants and interior plantscapes.

Adult fungus gnats may emerge from

houseplants indoors and become

a nuisance.

IDENTIFICATION

Fungus gnats ( Orfelia and Bradysia spe -

cies), also called darkwinged fungus

gnats (Sciaridae), are dark, delicate-

looking flies similar in appearance to

mosquitoes. Adult fungus gnats (Figure

1) have slender legs with segmented

antennae that are longer than their

head. Their long antennae distinguish

them from the more robust shore flies,

which are also found in greenhouses,

associated with algae and decomposing

organic matter, but have short bristle-

like antennae (Figure 2). Although a few

species are up to 1 ⁄ 2 inch long, fungus

gnat adults commonly are about 1 ⁄ 16

to 1 ⁄ 8 inch long. Wings are light gray to

clear, and the common Bradysia species

have a Y-shaped wing vein (Figure 3).

Because adult fungus gnats are at -

tracted to light, you first might notice

these pests flying near windows in -

doors. However, in comparison with

more active species such as the com -

mon housefly ( Musca domestica ), fun -

gus gnats are relatively weak fliers and

usually don’t move around much in -

doors. Fungus gnats often remain near

potted plants and run across (or rest

on) growing media, foliage, compost,

and wet mulch piles.

Females lay tiny eggs in moist organic

debris or potting soil. Larvae (Figure

4) have a shiny black head and an elon -

gated, whitish-to-clear, legless body.

They eat organic mulch, leaf mold,

grass clippings, compost, root hairs,

and fungi. If conditions are especially

moist and fungus gnats are abundant,

larvae can leave slime trails on the sur -

face of media that look like trails from

small snails or slugs (Figure 5).

DA M AGE

Adult fungus gnats don’t damage

plants or bite people; their presence is

primarily considered a nuisance. Lar -

vae, however, when present in large

numbers, can damage roots and stunt

plant growth, particularly in seedlings

Figure 1. Fungus gnat adult caught in a yellow sticky trap.

Figure 2 . Fungus gnat adult (left) and shore fly (right). Note the more robust body and shorter antennae on the shore fly.

Figure 3. A Y-shaped wing vein distinguishes common fungus gnats from most other small flies in the home and greenhouse.

Figure 4. Fungus gnat larvae.

Figure 5. Shiny trails on the soil surface made by fungus gnat larvae.

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and young plants. Significant root dam -

age and even plant death have been

observed in interior plantscapes and

in houseplants when high populations

were associated with moist, organical -

ly-rich soil. Thus, a houseplant that is

wilting may not indicate a lack of wa -

ter, but rather root damage by fungus

gnat larvae or (more commonly) other

causes of unhealthy roots. However,

too much or too little water, root decay

fungi, and improper soil conditions

(e.g., poor drainage, or waterlogging)

are much more common causes of

wilted plants.

Serious fungus gnat damage is more

common in greenhouses, nurseries,

and sod farms. Although larvae also

feed on plant roots outdoors, they don’t

usually cause serious damage.

LI F E C YC LE

Fungus gnats develop through four

stages—egg, larva (with four larval

stages or instars), pupa, and adult. The

tiny eggs and oblong pupae occur in

damp organic media where females

lay eggs and larvae feed. At 75ºF, eggs

hatch in about 3 days, the larvae take

approximately 10 days to develop

into pupae, and about 4 days later the

adults emerge. A generation of fungus

gnats (from female to female) can be

produced in about 17 days depending

upon temperature. The warmer it is,

the faster they will develop and the

more generations will be produced

in a year.

Fungus gnats have many overlapping

generations each year. Outdoors, they

are most common during winter and

spring in interior areas of California,

when water is more available and cool -

er temperatures prevail. They can occur

during any time of the year in moist

coastal regions and indoors.

MANAGEMENT

Most of the fungus gnat’s life is spent

as a larva and pupa in organic matter

or soil, so the most effective control

methods target these immature stages

rather than attempting to directly

control the mobile, short-lived adults.

Physical and cultural management

tactics—primarily the reductions of ex -

cess moisture and organic debris—are

key to reducing fungus gnat problems.

Commercially-available and naturally-

occurring biological control agents can

also control this pest. Insecticides are

considered an important control option

in some commercial plant production

but generally aren’t recommended

for fungus gnat management in and

around the home.

Monitoring

Visual inspection for adults usually

is adequate for determining whether

a problem exists. You will see adults

resting on plants, soil, windows, or

walls, or you might see them in flight.

Besides looking for adults, check plant

pots for excessively moist conditions

and organic debris where larvae feed.

Yellow sticky traps can be used to trap

adults. Chunks of raw potato placed in

pots with the cut sides down (not the

peels) are sometimes used to monitor

for larvae.

Water and Soil Management

Because fungus gnats thrive in moist

conditions, especially where there is an

abundance of decaying vegetation and

fungi, avoid overwatering and provide

good drainage. Allow the surface of

container soil to dry between water -

ings. Clean up standing water, and

eliminate any plumbing or irrigation

system leaks. Moist and decomposing

grass clippings, compost, organic fer -

tilizers, and mulches are also favorite

breeding spots. Avoid using incom -

pletely-composted organic matter in

potting media unless it is pasteurized

first, because it will often be infested

with fungus gnats. Improve the drain -

age of the potting mix (e.g., increase

the proportion of perlite or sand in the

mix). Minimize organic debris around

buildings and crops . Avoid fertilizing

with excessive amounts of manure,

blood meal, or similar organic materi -

als. Screen and caulk leaky windows

and doors to help prevent pests from

coming indoors.

If you have infested plants, don’t move

them to new areas where flies can

emerge to infest other pots. In some

cases you may wish to toss out severely

infested plants.

Purchase and use only pasteurized

container mix or potting mix. Com -

mercial growers often treat potting soil

with heat or steam before using it; this

will kill flies and the algae and micro -

organisms they feed on. Home garden -

ers can solarize soil:

1. Moisten it.

2. Place it in a bag of transparent

plastic or black plastic.

3. Make the pile no deeper than

about 8 inches.

4. Place the bagged soil on a slightly

elevated surface, such as a pallet

in a sunny location, for about 4 to

6 weeks.

See the Pest Note: Soil Solarization listed

in the references for details. Store pas -

teurized potting soil off the ground

and in closed containers to prevent it

from becoming infested before use.

Tr a p p i n g

In home situations where fungus gnat

adults are a nuisance, it may be pos -

sible to reduce the problem by using

sticky traps available at retail nursery

and garden centers. Yellow sticky traps

can be cut into smaller squares, at -

tached to wooden skewers or sticks

and placed in pots to trap adults. Also,

raw potato chunks placed in the soil

are very attractive to fungus gnat

larvae. These may be used not only to

check pots for larvae but also to trap

them away from plant roots. After a

few days in a pot, remove infested

chunks, dispose of them, and replace

with fresh ones.

Biological Control

Three commercially available biological

control agents can be purchased to con -

trol fungus gnats in pots or container

media (Table 1). These include Steiner -

nema nematodes, Hypoaspis predatory

mites, and the biological insecticide

Bacillus thuringiensis subspecies israelen -

sis (Bti). Several Bti products (Mosquito

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Table 1. Commercially Available Biological Pesticides and Natural Enemies for Controlling Fungus Gnat Larvae.

Biological Comments

Bacillus thuringiensis subspecies israelensis (Bti) (Gnatrol) A naturally occurring, spore-forming bacterium produced commercially by fermentation. Bti applied at labeled rates provides temporary control and is toxic only to fly lar vae, such as mosquitoes, black flies, and fungus gnats. Repeat applications commonly are needed for long-term control. This Bt is a different subspecies from that applied to foliage to control caterpillars. Bt labeled for caterpillars is not effective against fly lar vae.

Hypoaspis (=Geolaelaps or Stratiolaelaps) miles A light-brownish predaceous mite adapted to feeding in the upper layers of moist soil. Preys on fungus gnat lar vae and pupae, thrips pupae, springtails, and other tiny invertebrates. Commercial mites commonly are shipped in a shaker-type container used to apply them. Recommended rates in commercial nurseries are about 1/2 to several dozen mites per container or square foot of media. Make applications before pests become abundant. Hypoaspis probably won’t per form very well in individual houseplants and probably isn’t a good choice for use in homes.

Steinernema feltiae This nematode is effective when temperatures are between 60° to 90°F and conditions are moist. You can apply it as a soil drench and to media using conventional spray equipment. Nematodes reproduce and actively search for hosts, so under moist conditions they can provide season-long control after several initial applications to establish populations.

Note: These materials are essentially nontoxic to people and are compatible for application in combination. Bt is available from many well-stocked nurseries and garden supply stores. Predaceous mites, Bti, and nematodes, are commercially available through mail order from special suppliers,

Bits, Gnatrol) are readily available in

retail nurseries and garden centers, so

these products may be the most con -

venient for home gardeners to use. Bti

does not reproduce or persist indoors,

so infestations in potting media might

require repeated applications at about

five-day intervals to provide control.

Nematodes and Hypoaspis mites must

be mail-ordered and are live and per -

ishable products, requiring immediate

application. Nematodes can provide

relatively long-term control of fungus

gnat larvae, and they can be self-repro -

ducing after several inoculative appli -

cations to establish their populations.

Steinernema feltiae is more effective

against fungus gnats than other com -

mercially available nematode species.

Mix Bti or nematodes with water, and

apply as a soil drench, or spray onto

media using a hand-pump spray bottle

or other spray equipment, following

label directions.

Several natural enemies help to man -

age fungus gnat populations in out -

door systems, such as landscapes and

gardens, and indoors in greenhouses

and conservatories, including the

predatory hunter flies, Coenosia spp.

These flies catch and consume adult

fungus gnats in mid-air, and prey on

fungus gnat larvae in soil while devel -

oping as larvae themselves. Conserve

these and other natural enemies by

avoiding broad-spectrum insecticide

applications.

Chemical Control

Insecticides are rarely warranted to

control these flies in and around homes.

However, if you do apply an insecticide

for fungus gnats, consider using Bti or

Steinernema feltiae nematodes to control

the larvae; see the section Biological

Control for more information.

If Bti or nematodes aren’t available and

high populations are intolerable, pyre -

thrins or a pyrethroid insecticide may

provide temporary, fast-acting control.

Spray the surface of potting soil and

plant parts where adults typically

rest. Do not aerially fog indoors or at -

tempt to spray adult gnats in flight.

Be sure the product is labeled for

your particular use (e.g., for “house

plants”) and read and follow the

product’s directions.

Pyrethrins have low toxicity to people

and pets and are the active ingredients

in the botanical pyrethrum, which is

derived from flowers of certain chry -

santhemums. Many products include a

petroleum-derived synergist (piperonyl

butoxide, or PBO) to increase pyre -

thrum effectiveness. Pyrethroids (e.g.,

bifenthrin, permethrin) are synthe -

sized from petroleum to be chemically

similar to pyrethrins; they often are

more effective and persistent but are

more toxic to beneficial insects. When

using these products on houseplants

or interiorscape containers, if possible

move plants outdoors for treatment as

a precaution, and wait about a day after

applying the chemical before bringing

them back inside.

For information on managing fungus

gnats in commercial flower, nursery

or greenhouse operations, see the

UC IPM Pest Management Guidelines:

Floriculture and Ornamental Nurseries

and the book Integrated Pest Manage -

ment for Floriculture and Nurseries listed

in the references.

ADAPTED FROM

Dreistadt, S. H. 2001 Pest Note: Fungus

Gnats, Shore Flies, Moth Flies and March

Flies . Oakland: Univ. Calif. Div. Agric.

Nat. Res. Publ. 7448.

REFERENCES

Cloyd, R. A. 2010. Fungus gnat man -

agement in greenhouses and nurseries.

Kansas State University Agricultural

Experiment Station and Cooperative

Extension Service. Publication MF-2937:
http://www.ksre.ksu.edu/bookstore/

p u b s/ M F 2 9 3 7. p d f

Dreistadt, S. H. rev. 1986. Fungus Gnats

and March Flies . Oakland: Univ. Calif.

Div. Agric. Nat. Res. Publ. 7051.

August 2013 Fungus Gnats

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AUTHORS: J.A. Bethke , UC Cooperative Extension, San Diego Co and S. H. Dreistadt , UC Statewide IPM Program, Davis.

TECHNICAL EDITOR: M.L. Flint

EDITORS: M.L. Fayard and C. Laning

ILLUSTRATIONS: Figs. 1-2 and 4-5 , J.K. Clark; Fig 3. , C. Feller.

This and other Pest Notes are available atwww.ipm.ucanr.edu .

For more information, contact the University ofCalifornia Cooperative Extension office in your county. See your telephone directory for addresses and phone numbers, or visit http://ucanr.org/ce.cfm .

WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either use the pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that they may contaminate water supplies or natural waterways.

ANR NONDISCRIMINATION AND AFFIRMATIVE ACTION POLICY STATEMENT The University of California prohibits discrimination or harassment of any person in any of its programs or activities. The complete nondiscrimination policy statement can be found at http://ucanr.org/sites/anrstaff/files/107734.doc. Inquiries regarding the university’s equal employment opportunity policies may be directed to Linda Marie Manton, Affirmative Action Contact, University of California, Davis, Agriculture and Natural Resources, One Shields Avenue, Davis, CA 95616, (530) 752-0495.

Produced by UC Statewide Integrated Pest Management ProgramUniversity of California, Davis, CA 95616

University of California scientists and other qualified professionals have anonymously peer reviewed this publication for technical accuracy. The ANR Associate Editor for Pest Management managed this process. To simplify information, trade names of products have been used. No endorsement of named products is intended, nor is criticism implied of similar products that are not mentioned. This material is partially based upon work supported by the Extension Service, U.S. Department of Agriculture, under special project Section 3(d), Integrated Pest Management.

Dreistadt, S. H., J. K. Clark, and M. L.

Flint. 2001. Integrated Pest Management

for Floriculture and Nurseries . Oakland:

Univ. Calif. Agric. Nat. Res. Publ. 3402.

Harris, M. A., R. D. Oetting, and W. A.

Gardner. 1995. Use of entomopatho -

genic nematodes and a new monitoring

technique for control of fungus gnats,

Bradysia coprophila (Dipt.: Sciaridae), in

floriculture. Biological Control 5:412- 418.

UC IPM Pest Management Guidelines:

Floriculture and Ornamental Nurseries .

Oakland: Univ. Calif. Agric. Nat. Res.

Publ. 3392. Also available online at

h t t p ://w w w. i p m . u c d a v i s . e d u/P M G/

selectnewpest.floriculture.html

Nielsen, G. R. 1997. Fungus Gnats.

Department of Plant and Soil Science,

University of Vermont Extension. Pub -

lication EL 50: h t t p ://p s s . u v m . e d u/p p p/

pubs/el50.htm

Stapleton, J.J.; C.A. Wilen, and R.H. Mo -

linar. 2008. Pest Notes: Soil Solarization.

Oakland: Univ. Calif. Agric. Nat. Res.

Publ. 7441. h t t p ://w w w. i p m . u c d a v i s .

edu/PMG/PESTNOTES/pn74145.html

Wright, E. M., and R. J. Chambers.

1994. The biology of the predatory mite

Hypoaspis miles (Acari: Laelapidae), a

potential biological control agent of

Bradysia paupera (Dipt.: Sciaridae). Ento -

mophaga 39:225-235. v

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