University of FloridaSolutions for Your Life

Download PDF
Publication #ENY-912

Management of Fungus Gnats in Ornamentals1

James Price, Lance Osborne, Curtis Nagle and Elzie McCord, Jr.2

Fungus gnats can be present in flower and foliage production areas most of the year, but hot rainy periods are ideal conditions for the development of high population levels. With proper fungus gnat management, growers can produce healthy crops and can ship potted plants free of the damaging and nuisance insects.

Biology

Fungus gnat adults (Figure 1) are about 1/8 inch long, slender flies with long legs and long, thread-like antennae. They look more like tiny mosquitoes than common flies. Larvae live in the soil and are difficult to find. If fungus gnats are present, larvae are most likely found in the early morning in the topsoil layer of a thoroughly wet pot. Larvae are translucent gray to white, about 1/4 inches long, worm-like with no legs, and with shiny black heads. There is no similar insect in the production area or interiorscape.

Figure 1. 

Fungus gnat adult.


[Click thumbnail to enlarge.]

These insects can infest a crop from soil or algae under benches, from contaminated potting soil or by flying short distances into the production area. Fungus gnats almost always are present in growing areas, at least at low densities.

Life Cycle

Females live about a week and lay 30 to 120 eggs singly or in batches of up to 30 on the soil. Eggs hatch in 4 to 7 days (Steffan 1966). Larval development requires about 8 to 20 days, depending upon temperatures. The resting pupal stage lasts about 3 to 5 days and is located near the soil surface.

Adult flies do not damage plants, but are objectionable to consumers and cannot be tolerated on potted plants in hospitals, grocery stores, or florist shops. Adults can emerge from immature forms after sale even when none were evident earlier.

Larvae feed on decaying matter and on healthy and diseased roots in soil media. They can be particularly damaging to seedlings and other small plants. Damaged roots provide conditions for root diseases, further complicating fungus gnat management and crop health.

Management

Sound crop management that denies fungus gnats the conditions necessary for development, and promotes parasites and predators of the pest will reduce the need for pesticides. Fungus gnat problems may result from over-wet soil conditions and diseased roots, and should alert growers to poor cultural conditions. Potting media should be stored dry; and pots and production areas should be well drained. Fungus gnats can exist on soil fungi, algae under benches, and on damp mossy benches. Some growers apply hydrated lime to eliminate fungal food sources.

Biological Control

Sometimes naturally occurring parasitic insects and predatory mites can become established and regulate fungus gnat populations. This frequently occurs when broad-spectrum pesticides are avoided in production areas. Fungus gnat parasites are tiny wasps, much smaller than fungus gnats and may be seen walking on pot surfaces. Predatory mites are tiny, almost round, dark brown, eight-legged inhabitants of the soil surface. Both agents attack immature fungus gnats but not the adults.

Adult fungus gnats are attracted to yellow sticky traps. These traps can be used to detect their presence. One can also look for adults moving on soil surfaces. If fungus gnats become a problem within a few weeks of anticipated sales of potted plants, a pesticide control program may be required.

Pesticides

Pesticides for controlling fungus gnats (Table 1) can be applied as drenches to pots or as sprays to foliage, pots, beds, or other soil surfaces as label directions indicate. Many of the products act as larvacides when applied as drenches to pots and soil underneath benches. Treated larvae will die, as will larvae that develop from the eggs already in the soil. However, these materials do not kill adults present at application nor the adults that will develop from pupae present at application. Therefore effects may seem disappointing for the first few days.

Hamlen and Mead (1979) demonstrated that some insecticides applied as sprays to soil surfaces were as effective for fungus gnat control as were drenches of the same materials. Sprays normally should be reapplied once or twice at 10-day to 2-week intervals.

The best growers stress good water management and good root health, and are prepared to use insecticides correctly when fungus gnats are not otherwise controlled. When such practices are followed, fungus gnats should not be a problem.

Table 1 summarizes the chemical control agents registered in Florida on various ornamental crops in production and for interiorscape maintenance. These include microbial insecticides that may be considered components of biological control. Pesticide labels sometimes specify product use on any “ornamental,” “foliage,” or “flower” crop and sometimes use only on specifically named flower or foliage crops. This summary provides the chemical options available for use in field, shade house and greenhouse production and interiorscape maintenance settings for any ornamental flower or foliage crop plus an additional options available for use on certain named flower or foliage crops.

Table 1 is organized into two target crop categories, beginning with a general category “All Flower and Foliage Crops.” This is followed by a short section that refers the reader to product labels to find specifically named flower and foliage crops.

Commercial products available for control of fungus gnats are grouped by active ingredient. Usually, only one example of any particular formulation is given. Other examples or other formulations may exist that are as effective as those mentioned. Notes are provided to qualify some uses and precautionary statements and re-entry intervals are given to aid in the safe use of the pesticides. Hyperlinks to pesticide labels are not provided, but a search at the Websites of CDMS (http://www.cdms.net/manuf/default.asp), C&P Press (http://www.greenbook.net/) or the product manufacturer may provide the desired label.

This summary is only a guide to aid in pesticide selections. Care has been given to provide accurate and up-to-date information, but it is possible that, through label changes, author error, etc., improper uses may be indicated. In all cases it is the applicator's responsibility to read and comply with the label that accompanies each pesticide container.

Warnings

All insecticides should be handled with caution and the safety precautions on the container must be followed. Wear personal protective equipment (PPE) as indicated. Read the entire label before opening the container. Avoid pesticide drifts to adjacent areas or to crops that may be eaten by man or animals. Do not allow pesticides to get into streams or water supplies. Store pesticides in their original labeled containers, out of reach of children, and pets. Store pesticides under lock and key. When containers are empty, rinse with water three times and pour rinsate into the spray tank. Dispose of empty containers promptly and safely.

As an additional precaution, keep the telephone number and address of the nearest county poison control center in a convenient location in case of an accidental pesticide poisoning. Also, keep clean copies of labels of all pesticides that are on the premises. In the event of a poisoning, the label of the pesticide involved should be taken to the poison control center or hospital. If a product is labeled for use specifically in Florida (special local need), purchasers should obtain a copy of the supplemental label from the supplier.

References Cited

Hamlen, R. A. and F. W. Mead. 1979. Fungus gnat larval control in greenhouse plant production. J. Econ. Entomol. 72(2):26971.

Steffan, Wallace A. 1966. A generic revision of the family Sciaridae (Diptera) of American North of Mexico. Univ. of Calif. Pub. in Entomol. 44-16-22.

Tables

Table 1. 

Pesticides registered for control of fungus gnats on various ornamental crops in production and interiorscape maintenance. Parenthetical information in the "Trade Name" column refers to the sites where the product is permitted for use: field production (F), greenhouse production (G), and interiorscape maintenance (I).

Common Chemical

Name

Trade Name (Site)1

Pre-

Caution

(Signal Word)

REI

(Hrs)2

Notes from Label3

AVAILABLE FOR ALL FLOWER AND FOLIAGE CROPS:

Acephate

1300 Orthene TR (G)

Caution

24

 

Acephate & Fenpropathrin

Tame/Orthene TR (G)

Warning

24

Do not apply within 48 hours of a previous application.

Acetamiprid

TriStar 30 SG, 70 WSP (F, G)

Caution

12

Larvae; do not make more than five applications per year. Do not apply more than (0.55 lb a.i./acre-) per year.

Azadirachtin

Azahar (F, G, I)

Caution

4

Do not add crop oils to spray mixtures intended for use on ornamentals.

 

Azatin XL (F, G, I)

Caution

4

 

Azatin EC (F, G, I)

Caution

4

Waxy bloom on certain ornamental plants may be reduced after an application. Applications may remove the glaucous 'blue' coloring from evergreens such as Colorado blue spruce and Koster spruce. Caution is recommended when making applications to orchid, poinsettia or violets; spotting of plant foliage and blossoms is possible.

Ornazin 3% EC (F, G, I)

Warning

12

 

Bacillus thuringiensis israelensis

Gnatrol (F, G, I)

Caution

4

Larvae; potting soil mixtures (F); soil drench

Beauveria bassiana

ATCC 74040

Naturalis L (F, G)

Caution

4

Do not tank mix with fungicides. Wait a minimum of 48 hours after application before applying fungicides.

Bifenthrin

Attain Greenhouse Microemulsion (G, I)

Caution

12

 

Attain Nursery Microemulsion (F,G)

Caution

12

Shadehouse & nursery (F)

Attain TR (G)

Danger

12

For commercial use only. Not for residential use.

Attain TR Micro (G)

Warning

12

For commercial use only. Not for residential use.

Bifenthrin Nursery Granular (F)

Caution

12

Larvae; balled and containerized nursrey stock.

Menace 7.9%

Flowable (I)

Caution

When dry

Adults

Menace GC 7.9% Flowable (F, G, I)

Caution

12

Larvae; Do not apply more than 0.2 lb. a.i. per acre per year for outdoor applications.

Onyx Insecticide (I)

Warning

When dry

Adults

Onyx Pro (F,I)

Warning

12

Adults

Talstar GC (I)

Caution

12

Adults

Talstar P (G, I)

Caution

12

Adults

Talstar Nursery Granular (F)

Caution

12

Larvae; containerized and balled nursery stock plantings; soil incorporation into potting media.

Talstar Select (F, G)

Caution

12

Shade house & nursery (F); do not apply more than 0.2 lb. a.i. per year for outdoor applications.

Bifenthrin & Imidacloprid

Allectus SC (1)

Caution

When dry

Broadcast applications can not exceed 9.0 pints per acre per year.

Chlorfenapyr

Pylon Miticide (G)

Caution

12

Early stage fungus gnat larvae (Bradysis sp.).

Chlorpyrifos

Duraguard ME (F, G)

Caution

24

Larvae; direct spray to some open blooms may cause petal drop. Do not spray on kalanchoes.

Chlorpyrifos & Cyfluthrin

Duraplex TR (G)

Warning

24

Not for residential use.

Cyfluthrin

Decathlon 20WP

(F, G, I)

Caution

12

 

Tempo 20WP, SC Ultra, Ultra WP (I)

Caution

When dry

 

Cyfluthrin & Imidacloprid

Discus (F)

Caution

12

Nursery; including grassy areas in and around nursery; application can not exceed a total of 244 oz. per acre per year.

Cyromazine

Citation (F, G, I)

Caution

12

Shade house (F); larvae

Deltamethrin

Deltaguard GC 5SC (F)

Caution

12

Nursery

Diflubenzuron

Adept (F, G, I)

Caution

12

Bed, bench & container-grown; shade house (F) & enclosed commercial structures (G). Do not apply to poinsettias, hisbiscus, and Reiger begoinia. Do not apply to plants grown on capillary water mats

Dinotefuran

Safari 20SG, 2G

(F, G, I)

Caution

12

Nursery & shade house (F); larvae

Imidacloprid

Benefit 60WP (F, G, I)

Marathon 1% G (F, G, I)

Marathon 60 WP (F, G, I)

Caution

12

Nursery, including grassy areas in and around nursery (F); larvae

Marathon II (F, G, I)

Caution

12

Ornamentals grown in flats, benches, or beds (F); larvae

Permethrin

Astro (G, I)

Caution

12

Do not apply more than 2.0 lb. a.i. per acre per year.

Dragnet SFR Termiticide/Insecticide (I)

Caution

When dry

 

Perm-Up 3.2 EC (F, G, I)

Caution

12

Nursery (F); marginal leaf burn may occur on salvia, dieffenbachia and pteris fern. Application to blooming plants may cause browning of petals.

Permethrin E-Pro (F, G, I)

Caution

12

Nursery stock (F); do not apply more than 2.0 lbs. A.I. per acre per year.

Tengard SFR One Shot (I)

Caution

12

 

Pyrethrins

Pyganic Crop Protection EC 1.4 (F, G, I)

Caution

12

 

Pyganic Crop Protection EC 5.0 (F, G, I)

Warning

12

 

Pyrethrins & Piperonyl Butoxide

Evergreen EC 60-6 (F, G, I)

Caution

12

 

Pyrenone Crop Spray (F, G, I)

Caution

12

 

Pyreth-It Formula 2 (F, G, I)

Caution

12

 

Pyrethrum TR (G)

Caution

12

 

Pyrethrins, Piperonyl Butoxide & N-octyl bicycloheptene dicarboximide

1600 X-clude (I)

Caution

When dry

Do not use on cyclamen and nasturtium.

Pyriproxyfen

Distance IGR (F, G, I)

Caution

12

For foliar spray application, apply Distance no more than two times per cropping cycle or no more than two times per 6 months. For sprench application, if a second application is needed, allow a minimum of 21 days between applications. For drench application: Do not drench plants more than one time per crop cycle. Do not apply to salvia, ghost plant, Boston fern, schefflera, gardenia or coral bells. Do not apply to poinsettia after bract formation.

Steinernema feltiae

Nemasys (F, G, I)

None

0

If fungus gnats are established it may take 2 to 3 weeks before the number of adults is noticeably reduced. Treat entire houses or plant inventory as soon as possible after placement in greenhouse. In propagation areas, treat new plants as they are introduced. Do not use through drip irrigation or mist system.

S-Kinoprene

Enstar II (F, G, I)

Warning

4

Shade house (F); Application should be made to poinsettia before bract formation. Foliar damage on some sensitive varieties can result. Some varieties of roses, such as yellow blooded roses, show delayed damage. Slight to moderate injury has occured on some blooms under certain conditions, suggest application be made in prebloom stage.

Thiamethoxam

Flagship 25 WG

(F, G, I)

Caution

12

Apply to soil or growing media; field nursery and shade house (F); do not exceed 17 oz. per acre per crop or year.

AVAILABLE FOR CERTAIN FLOWER AND FOLIAGE CROPS (SEE LABEL TO DETERMINE WHICH CROPS):

Refined Petroleum Distillate

Purespray Green (G)

Saf-T-Side Spray Oil (G)

Ultra-Fine Oil (G)

Ultra-Pure Oil (G)

Caution

4

Oil removes the glaucous (blue) bloom from such evergreens as Colorado blue spruce and Koster spruce. See labels for warnings about phytotoxicity and chemical incompaibilities.

1Usually only a few examples of each formulation are given. There may be other products available that are as effective as those listed.

2REI = Re-entry Interval or period between application and earliest normal entry into treated area.

3Notes are taken from product labels and restrict use to the condition indicated (suppression, adults, containerized plants, etc.), limit number or patterns of applications, provide phytotoxicity precautions, etc.

Footnotes

1.

This document is ENY-912 (IG125), one of a series of the Department of Entomology and Nematology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first printed: October 1993. Revised: September 2011. Please visit the EDIS website at http://edis.ifas.ufl.edu.

2.

James Price, associate professor, GCREC, Wimauma, Lance Osborne, professor, CFREC, Apopka, Curtis Nagle, biologist, GCREC, Wimauma, Entomology and Nematology Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611 and Elzie McCord, Jr., associate professor of Biological Sciences, New College of Florida, Sarasota, 34243.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.