Species

Fungus gnats belong to the order Diptera and the families Myctophilidae and Sciaridae.

Host/Site

Fungus gnats larvae are generally found in soils with high percentages of organic matter.

They are regularly found on houseplants such as poinsettias, gerberas, daisies, gloxinias, cyclamens, hybrid impatiens, geranium, ornamental peppers and most bulb plants.

Identification

Indicators
Look for brown scarring on roots as well as irregular stunted growth. In severe cases fungus gnat infestations will cause wilting and even plant death. Often plant wilting will not be attributed to fungus gnats until roots are examined. Fungus gnats also transport and spread plant diseases such as Pythium, Verticillium, Cylindrocladium, Scelerotinia, and Theila-viopsis. The effects on these diseases on your garden can be devastating.

Life Cycle

Adult fungus gnats lay about 200 eggs in moist areas with large amount of organic matter. Larvae hatch in four days and feed on plant roots, fungus, and other organic materials for two weeks before pupating. After 4-5 days adults emerge. The entire life cycle lasts 3-4 weeks. Multiple generations can be born each year especially in moist climates.

Natural Enemies

Parasitic nematodes and predatory mites are natural enemies of fungus gnats. See Biological Controls below for more information

Monitoring

Since fungus gnat larvae live and feed under the soil and therefore it can be difficult to recognize their presence until damage has already been done.

One monitoring technique that will help you detect the presence of fungus gnats as well as the size of the infestation is a yellow stick trap. Yellow stick cards are most effective when placed horizontally on the potting media surface, although vertically positioned cards hung over the crop canopy are also effective and trap more of other types of insect pests as well. Cards placed under the benches, close to intake vents, near doorways and outside the greenhouse can provide additional information to detect breeding areas. Continuous monitoring (weekly) can provide the following information: 1) first detection of low populations; 2) population density increases or decreases over time; 3) the level and length of suppression resulting from the implementation of suppression tactics.

Action Threshold

Many species of fungus gnats do not harm plants, and their presence is a mere nuisance. Action should be taken when physical signs of damage such as wilting begin to occur.

Fungus gnats are potential vectors of plant diseases such as Botrytis, Fusarium, Verticillium, Pythium, and Phoma. If these diseases are noted, consider the possibility of fungus gnats and taking action to control them.

Physical/Mechanical Controls

Light/electrocution traps can be effective controls as well as monitoring tools, especially in small greenhouses or gardens.

A nearby planted trap crop can be effective. A.L. Antonenelli of Washington State University suggests that sprouted wheat is an effective trap crop because of the fungus gnat's affinity for this plant. After two weeks, discard the plant and its soil outside or submerge in boiling water. Repeat until fungus gnats are no longer damaging to your plants.

Since fungus gnat larvae thrive in moist conditions, avoid overwatering of plants and make sure that potted plants have adequate drainage.

Keep compost piles and decaying organic matter away from greenhouses and garden beds. Never use compost in your garden until it is fully decomposed.

Biological Controls

The Predatory Mite Hypoaspis spp. is an effective predator against fungus gnats. Predatory mites are also effective biological controls for thrips, pestiferous spider mites, psocids and other small, soil-dwelling pests.

Parasitic Nematodes of the species S. feltiae are another effective biological control.

Chemical Controls

The bacterial insecticide Bacillus thuringiensis isrealensis or Bti can be an effective biological control. It is also effective as a control for the larvae of mosquitoes and blackflies.

Pesticides such as carbamates, organophosphates and pyrethroids are extremely toxic to beneficial predatory mites, and should not be used.

References

Drees, Bastiaan M., "Fungus Gnat Management." 1994. The Texas Agricultural
Extension Service. 16 Oct 2008. < http://insects.tamu.edu/extension/ bulletins/uc/uc-028.html>.

Dreistadt, S. "Fungus Gnats, Shore Flies, Moth Flies, and March Flies Management Guidelines." University of California IPM Program. 16 Oct 2006.< http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html>.

Olkowski, William, Sheila Daar and Helga Olkowski. Common-Sense Pest Control: Least-Toxic Solutions for Your Home, Garden, Pets, and Community. Newtown, CT: Taunton Press, 1991.

Pundt, Leanne. "Fungus Gnats are Serious Pests." 1999. University of Connecticut IPM. 16 Oct 2008.
<http://www.hort.uconn.edu/IPM/greenhs/htms/fngnatser.htm>.