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Purple Power

Pest: Fungus Gnats

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                                                                 Pest: Fungus Gnats


 (Families Mycetophilidae (Order: Diptera), Sciaridae, Excechia, Diadocidiidae, Keroplatidae, and, Bolitophilidae)






Special Species Notes:



A common pest of plants grown indoors, especially where humidity and moisture are high.  Fungus Gnats can be told apart from Whiteflies because they're dingy grey instead of pure white. Larvae are most damaging to seedlings, cuttings and young plants.


Fungus Gnat larvae, small worms found in the top inch or two of your soil, feed mostly on organic debris. While doing this, they often nibble the roots of young seedlings.


Some fungus gnats are exceptionally hardy, they able to tolerate cold conditions through their possession of antifreeze proteins. overwintering organisms can either avoid freezing or tolerate freezing, but Excechia nugatoria can do both. For E. nugatoria, the production of noncolligative antifreeze proteins which protect the head and thorax from freezing, but they do not protect the abdomen. By allowing the abdomen to freeze, evaporative water loss is reduced over the course of the winter, and is the only insect known to semi-freeze through the winter.



First signs:


They’re usually first noticed when the harmless adults are seen flying around house plants or gathered at a nearby window or light. They are attracted to light. Small, dingy grey, non-biting flies, flying around plants aimlessly. If these "flies" are also seen coming out of the soil around your plants, you probably have Fungus Gnats. But it’s the larval stage, feeding in the soil, that can damage tender plant roots.


Plants may have sudden wilting, loss of vigor, poor growth, and yellowing. With severe infestations, a considerable portion of the plants may be lost.


Larvae, however, when present in large numbers, can damage roots and stunt plant growth, particularly in seedlings and young plants. Significant root damage and even plant death have been observed in interior plants when high populations are associated with moist, organically-rich soil.


plant that is wilting may not indicate a lack of water, 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.






Adults are delicate, grayish black, mosquito-like flies with long slender legs with segmented antennae that are longer than their head. Their long antennae distinguish them from the more robust shore flies, and one pair of clear wings. Fungus gnats (Orfelia and Bradysia species), also called darkwinged fungus gnats (Sciaridae), are dark, delicate-looking flies similar in appearance to mosquitoes. 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.


They are not strong fliers and emerge from potted plants, especially when watering. They usually don’t move around much indoors. 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 or maggots (1/4 inch) have a shiny black head and an elongated, whitish to transparent legless body. They are most abundant in damp, rich soils and feed on root hairs, fungi, debris, algae, and other organic materials. If conditions are especially moist and fungus gnats are abundant, larvae can leave slime trails on the surface of media that look like trails from small snails or slugs.





Shiny trails on soil by fungus gnat larvea



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.



Life cycle:


Because of their proclivity and relative short gestation, potted plants can host each stage, — egg, larvae (four larval stages or instars), pupae, adult — in multiple generations at once. The entire life cycle from egg to adult may be completed in as little as 3-4 weeks depending on temperature.


Adults live about one week and lay up to 300 eggs in rich, moist soils.


Within 3-6 days tiny larvae emerge and begin feeding on plant roots during their two week period. At 75ºF, eggs hatch in about 3 days, The warmer it is, the faster they will develop and the more generations will be produced. The larvae take approximately 10 days to develop into pupae. The pupal stage lasts 3-4 days before young adults emerges from the soil and begin the next generation.


Because of this remedies usually require repeated applications until there are no surviving eggs.

What they eat:

Moist and decomposing grass clippings, compost, leaf mold, organic fertilizers, root hairs, fungi,  and organic mulches

Controls: Yellow sticky traps Diatomaceous Earth: http://freemygreenpdx.com/topic/14332-diatomaceous-earth-de/

For presentation


Inspect plants thoroughly prior to purchase or accepting donation for signs of insect pests. Turn up soil carefully near the base of the plant and look for the glossy, clear larvae. Either reject any plant sending up flying gnats or if you have a quarantine area, place them there and address the pests: http://freemygreenpdx.com/topic/14249-quarantine-what-is-it-and-why-do-i-need-to/


Fungus gnats do best in damp soils; be careful not to overwater, especially during winter months when plants use less. When potting, avoid water holding, organic material such as peat moss that may encourage egg laying. Clean up standing water, if they is water in the saucer, dump it. Improve the drainage of the potting mix.


If pests are present, allow the soil to dry to a depth of one to two inches between watering. This not only kills larvae and inhibits the development of eggs, it also makes the soil less attractive to egg-laying females.


Avoid fertilizing with excessive amounts of manure, blood meal, or similar organic materials.

If you have infested plants, don’t move them to new areas where flies can emerge to infest other pots.


Avoid using incompletely-composted organic matter in potting media unless it is pasteurized first, because it will often be infested with fungus gnats.


The pasteurized process is also called, Soil Solarization. It is a nonchemical method for controlling soilborne pests using high temperatures produced by capturing radiant energy from the sun. When properly done, the top 6 inches of the soil will heat up to as high as 140°F, depending on the location. The plastic sheets allow the sun’s radiant energy to be trapped in the soil, heating the top 12 to 18 inches and killing a wide range of soilborne pests, such as weeds, pathogens, nematodes, and insects. greatest at the surface of the soil and decreases at deeper soil depths. The maximum temperature of soil solarized in the field is usually 108° to 131°F at a depth of 2 inches and 90° to 99°F at 18 inches. Control of soil pests is usually best for organisms found in the upper 6 inches of earth. Soil solarization also speeds up the breakdown of organic material in the soil, often resulting in the added benefit of release of soluble nutrients such as nitrogen (N03-, NH4+), calcium (Ca++), magnesium (Mg++), potassium (K+), and fulvic acid, making them more available to plants.


To pasteurized potting soil, it is done with heat or steam before using it; this will kill flies and the algae and microorganisms they feed on.


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.


Raw potato chunks placed in the soil are very attractive to fungus gnat larvae. The cut side down facing soil. 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.




Pyrethrins 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 attempt to spray adult gnats in flight. they often are more effective and persistent but are more toxic to beneficial insects.


Beneficial insects:


Predator Nematodes(long-term control, species Steinernema feltiae) http://freemygreenpdx.com/topic/14383-beneficial-predatory-nematodes/

 Fungus Gnat Predators (Hypoaspis sp.)


Biological insecticide Bacillus thuringiensis subspecies israelensis (Bti). Bti does not reproduce or persist indoors, so infestations in potting media might require repeated applications at about five-day intervals to provide control.


Bti and nematodes can be mixed with water, can be applied as a soil drench, or spray onto media using a hand-pump spray bottle or other spray equipment, following label directions.


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 developing as larvae themselves.


Mycorrhizae should help repair the damage/ grow roots faster: http://freemygreenpdx.com/topic/14315-mycorrhizae-and-the-roots/



The link below will take you to "An Intro to beneficial bugs and beneficial insect food" it has a list (been worked on) to pests and beneficial insects




Classy, sassy, and a bit of a smart assy

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Fungus gnats are a common pest of indoor plants, especially where the levels of moisture and humidity are quite high. They thrive in wet, rich soils and consume fungi, root hairs, and other organic materials from the soil. We faced the major infestation of fungus gnats in our indoor garden. We tried the DIY tips but it only gave us relief for a temporary time period. Tired of the problem, when we consulted Granite Bay pest control experts they suggested us to use beneficial nematodes or try vinegar trap idea. Eventually, these ideas worked out and we were able to get rid of the gnats problem.

Edited by EricGregory

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