The scoop on gnats: the weather they like & why they drive us nuts

A Fungus gnat ( )

No matter what type of gnat you’re looking at, one thing is for sure: gnats are annoying. Anyone who has swallowed a few while biking along Rock Creek at dawn or dusk can attest to that.

What is it about summer that entices these tiny flies to wake up and smell the … rotting roses? Gnat larvae live in moist environments. Given the average annual precipitation of 40 inches and ample waterways and wetlands in the DC region, finding the perfect gnat breeding site does not seem to be a problem.

With no end to heat and humidity in sight, perhaps Capital Weather Gang should create another daily forecast for our readers who are outdoor enthusiasts: the GnatCast.

You may think a gnat is just a gnat. But to an entomologist, it’s a fungus gnat, eye gnat, gall gnat, sand gnat, or any number of other small biting flies that are often mistaken for gnats, such as the fruit fly.

Gnats are small flies of the suborder Nematocera, which also includes midges, craneflies and mosquitoes. Whether we like them or not, gnats serve a purpose in nature. They are an important food source for birds, bats and larger insects. They also pollinate flowers.

They are not blood-thirsty like their cousin the mosquito. In fact, some adult gnats don’t even eat during their short lifespan. Gnat larva, which hatch from eggs laid in moist soil and other wet environments, feast on fungus, algae or plants.

Besides humidity, a gnat’s life cycle also depends on temperature. Take fungus gnats , for example. The fungus gnat – a common indoor pest that thrives in the overwatered soil of potted plants or greenhouses – lives out its life cycle in three to four weeks at temperatures of 77 degrees Fahrenheit or higher. Temperatures that are too hot can kill them (some horticulturalists have used a ‘bake-out’ method to rid greenhouses of fungus gnats by heating the soil to a temperature the gnats cannot withstand). On the other extreme, fungus gnats that live in Alaska can survive temperatures lower than 25 degrees below zero by freezing their bodies.

Gnats and related flies are so in sync with weather conditions that one team of scientists from the University of Liverpool has been analyzing fossilized midge heads to determine past climate events.

Ridding our homes and gardens of gnats can be a challenge, both indoors and out, especially after above average rainfall and relentless humidity and heat. Keeping storm drains unclogged and getting rid of standing water on your property may help. Try not to bring outdoor potted plants indoors. If your indoor plants become infested, let the soil dry out for a few days before watering again. Gnats in natural areas may be attracted to sweet scents, such as perfume and soaps, so avoid spraying yourself with strong-smelling products before heading outside.

Are gnats a nuisance to you this summer? Let us know and share your tips for getting rid of them by posting a comment below.


Uncle John knows pretty much everything—and if he doesn’t, he heads his massive research library, or puts one of his many associates on the case. So go ahead: In the comments below, ask Uncle John anything. (And if we answer your question sometime, we’ll send you a free book!) This week’s question comes from reader Lisa P., who asks…

What is the purpose of a gnat?

Ah, summer. Barbecues! Trips to the beach! Tiny, annoying insects buzzing around your face and flying up your nose! Yes, the gnat is as indelible a part of summer as the Fourth of July and sunburns, but they really do serve a purpose in the intricate web of nature.

Similar to how sardine is an umbrella term for any number of small, can-worthy fish, no one single bug is a gnat. There are dozens of species in three different flying insect families, although the one you’re thinking of is the common gnat, or Culex pipiens, a relative of the more volatile but equally annoying mosquito.

Gnats travel in swarms (called ghosts) around stagnant water, forests, and your facial orifices. Not only that, but they’re especially fond of feasting on houseplants, from the leaves down to the roots, killing them slowly before you even know the damage has been done.

So just how does the gnat justify its existence? The purpose of a gnat is to get eaten by creatures higher up on the food chain that are a little less annoying to us humans: birds and bats, mostly, although some other insects eat gnats. They also pollinate flowers that grow in moist soil along waterways.

However, to the gnat’s credit, they don’t eat blood like their mosquito relatives. Some gnats live for just a few days and don’t even eat at all during their short lives. That’s because they feast in their larval state, on fungus and algae, which can be invasive.

San Diego Reader

Dear Matthew Alice:

In the hallway in my condo complex. there is one shady section in which the air is thick with hovering little gnats. They are very annoying. But they never seem to bite or Sling anyone. What do they do? What do they eat? Do they sleep? Where do they go at night? What enjoyment can they possibly gain from flying around in the same place all day? Please help.

R. Betz, Rose Canyon

It will be no surprise to hear that your hall loiterers are from the group known as syrphid or hover flies. On the Matthew Alice annoyance scale, they hardly register at all. Are yours some mutant strain that travels with little ghetto blasters or makes rude comments to women as they come in the building? When I consider some of the neighbors I’ve had over the years, all, ostensibly, from the group homo sapiens … two late-night-party-throwing Neil Diamond fans who owned four spiteful, raucous chihuahuas; Mr. Guns-and-Motorcycles, who inspired the rest of us to form a Neighborhood Watch committee just to keep an eye on him; a middle-aged woman in primal-scream therapy …. If hover flies get you riled up, maybe your past has lacked a certain amount of color.

Be that as it may, the lives of these little bugs are simple enough. Eat and be eaten constitute their daily reality. Hall-hovering is their effort to avoid the second of these and to escape the sun on a hot day. I’m sure you’ve noticed the flies are most likely to appear during a heat wave. Ordinarily, syrphid flies hover under shady trees so their movements will be less noticeable to birds and other predators. But as man invades the natural landscape, hover flies have taken advantage of new opportunities and are just as content to hide out in a shady condo. If today’s wildlife were to adopt a license-plate motto, it would definitely be “Adapt or die.”

Adult hover flies are strictly vegetarians.

They don’t bite you because they have no stinging apparatus and because blond is not on their menu. They much prefer plant carbohydrates — nectar, pollen, that sort of thing. At egg-laying time, they’re partial to wild fennel and other plants that attract aphids. As for nightlife, hover flies aren’t very good partiers. Come dark, they would rather sleep under some protective covering. Check out the upper comers of your hallway, when: the walls and ceiling meet. If they haven’t escaped sometime in the evening, you may find them snoozing there. And as for what fun there is in hovering, the only payoff is surviving another day. I can sympathize.

Why syrphids hover is an elusive question. But the habit certainly has some social/reproductive or survival benefit. Bug motivations are not the stuff of which tangled Freudian theories are made. The flies seem to have an acute visual sense and a good feel for how far away they are from one another (and from you). If you approach a group slowly, the whole mass will move away as a unit, nobody bumping into anybody else or losing his place in the formation.

I know this is an unlikely scenario, but if you were to scrutinize a hover fly closely, you’d see that it’s actually quite colorful. Its body is brightly marked with black and yellow bands, much like a bumblebee. And if the fog of bugs is truly aggravating to you, perhaps you might tum your attention to the real problem: your neighbors who leave the front door open and let in the flies in the first place.



Color: They are gray to black in color.

Characteristics: Gnats are typically small, slender flies with long legs and lengthy antennae. You may have noticed them flying aimlessly about your house whether by themselves or in a group. Although these flies are often mistaken for babies because of their small stature, they are actually full grown when you see them flying about.

Size: About 2.5 millimeters long.

Potentially Dangerous: Not to people, but possibly to household plants and seedlings.

Nuisance Pest

What Do Gnats Look Like?

Adult gnats are very small- typically less than 1/4 of an inch long; they can be yellowish, tan or dark brown in color. Gnats have distinctive long legs and are weak fliers. The common gnat can often be identified by seeing swarms of gnats are often seen at dusk, these are the males of the species gathering in mating groups.

Why Do I Have Gnats?

Gnats are at their highest numbers in the summer when the weather is humid and moist; their activity generally decreases outside during the cooler dryer months. Some gnat species are attracted to homes and properties that have high levels of moisture, especially in the soil (fungus gnats).

Gnats will enter into your home while searching for food; they may also enter into homes on plants that are already infested with gnats or their eggs, or on items purchased from the store that are already infested. Gnats can reproduce very quickly so just a few can quickly turn into many and can become a huge nuisance in and around your home.

What Are The Feeding Habits Of Gnats?

Gnats can either be biting or nonbiting depending on the species. Gnats can be found feeding on plants, soil, fungus, other insects, or even on blood.

What Threats Do Gnats Pose?

Fungus gnats do not bite or sting but their larvae can cause damage to your houseplants and seedlings as they feed on the roots or burrow into their leaves and stems. Other species of gnats will bite and feed on the blood of people, pets, and livestock. Some species of gnats (black gnat) can spread a variety of dangerous diseases including river blindness.

How Do I Control Gnats?

Gnats are not a pest that many homeowners are successful in eliminating. Do-it-yourself methods of pest control often times prove ineffective and they can expose your family to harmful chemicals if not handled correctly. To prevent these pests from laying eggs it is best to try and eliminate water sources from your property; even stagnant water is attractive to a female, adult gnat. You can also water your plants less. Reducing the amount of water normally used for your plants can help dry the first couple of inches of soil, which will in turn keep any larvae from developing into gnats. However if you have an existing gnat problem it is best to contact a professional for help. The professionals at Holder’s understand the behavior patterns of these pests. For effective pest methods that can help get rid of pests, such as gnats; contact Holder’s Pest Solutions today!

How Do You Prevent Gnats?

Preventing gnats can be a difficult task but there are some things that you can do around your home or property to help control and prevent them. The best way to prevent gnats is to make sure that plants and gardens are not overwatered; and make sure that gutters are free of clogs and working properly to direct water away from your home. Inspect door and window screens checking that they are intact and that any gaps found around window and doors are sealed-this will help to prevent gnats from entering into your home. Keep fruits and vegetables in the refrigerator and regularly remove trash from your home. A professional will be able to identify problem areas and give a proper diagnosis of the situation.

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How to ID Fruit Flies, Drain Flies and Fungus Gnats

Drains can build up sludge that attracts fruit flies and drain flies. TERRO® has solutions for dealing with both of these pests.

When your home is under siege by tiny little flying insects, it can be easy to assume that you’re battling fruit flies, but that may not always be the case. Your problem may indeed be fruit flies, but two other insect species, the drain fly and the fungus gnat, should also be on your hit list.

Dealing with each of these species requires different tactics, so your first goal should be to identify the invader.


Without a doubt, fruit flies are the most common flying insects that will pester you in the kitchen. They are attracted to fresh and decomposing fruit as well as sugary juices and alcohol.

  • Colors: The two most common fruit flies, the Red Eyed Fruit Fly and the Dark-Eyed Fruit Fly, have striped abdomens. Their eye colors are, as the name suggests, red or black, respectively.
  • Size: Red Eyed Fruit Flies are about ⅛-inch long. Dark Eyed Fruit Flies are a bit bigger, at about 3⁄16-inch long.
  • Body type: Similar to a house fly, but much smaller.
  • Where: Fruit flies may be buzzing around your fruit bowl, inside a trash receptacle, in a recycling bin or in your drain or garbage disposal.


If you spot a swarm of bugs flitting above a houseplant, you probably have fungus gnats instead of fruit flies. Fungus gnat larva and pupa prefer moist soil to protect them as they develop. Before they progress to adult form, they can severely damage the root system of your potted plants.

  • Colors: Adults – brown or black with light colored legs.
  • Size: Adults are less than ⅛-inch long. Their larva and pupa forms are about the same size.
  • Body type: Although they are technically flies, they have a mosquito-like appearance.
  • Where: Fungus gnats will be spotted flying close to your potted plants and will show little interest in going anywhere else as long as there is moist soil available.


These hairy bugs are another kitchen pest. They thrive in dark, damp conditions and often find an ideal home inside a drain, which can include a floor or a sink drain, sink overflow or another area open to plumbing. Although they don’t bite, their presence can aggravate asthma in some people.

  • Colors: Light gray or tan with a dark border around wings.
  • Size: About ⅛-inch long.
  • Body type: Moth-like with fuzzy bodies and antennae.
  • Where: Drain flies breed inside of drains, often laying eggs in the sludge that accumulates inside. Adults will clumsily fly out of the drain and land nearby on walls and ceilings.


The best way to get rid of fruit flies is to keep your kitchen and garbage receptacles clean of any accumulated debris that may attract them. This includes thoroughly rinsing out beverage containers, using fruit quickly or placing it in the refrigerator, sealing garbage cans and removing refuse regularly from the area.

As you continue to work on preventing fruit flies, place TERRO® Fruit Fly Traps around the area to attract and trap any lingering adult fruit flies. Even better, these attractive traps have a decorative look which allows them to sit on countertops, windowsills and kitchen islands without attracting the attention of your human guests.

If your fruit fly problem persists, the issue may lie in your drain. Sludge and other organic material that attracts these pests can build up and provide an egg-laying area for these bugs, even if you repeatedly try to flush out the system. To clean this problem area, run a drain cleaner through your plumbing.


Preventing fungus gnats should begin when you first purchase a houseplant. Before bringing it into the home, pull it out of the pot and look for signs of these pests, including glossy, clear larvae. Obviously, any plant that already has gnats flying around it should be left at the store.

The other simple prevention method is to ensure that your plants aren’t overwatered. Fungus gnats prefer moist material to deposit their eggs. Further, avoid adding water-retaining material when potting a plant such as peat moss.

If you have fungus gnats, add Safer® Brand Houseplant Sticky Stakes to your pots. These stakes contain simple yellow-colored glue traps that attract adult fungus gnats. By attracting and killing off the adults, you will eventually eliminate most of the remaining gnats as they reach the adult stage. Additional control efforts should include allowing your plant soil to dry out and applying “beneficial nematodes.” These are tiny worms that seek out and eat the larvae of fungus gnats without damaging your plant or becoming pests themselves.


Eliminating drain flies requires a few steps. Once you recognize that you have drain flies, put some tape over the drains where you suspect they are emerging and leave it overnight. The next day, check to see if any flies have been collected. Once you know their source, you can begin eradication:

  • Clean the drain. Pour 2 to 4 quarts of warm water down the drain to moisten any material stuck inside. Then use a metal pipe brush or plumbing snake to break up and pull out any grime or sludge.
  • Add drain cleaner. Pour a gel down the drain and follow its instructions for use.
  • Flush the system. A few hours after applying the drain cleaner, flush more warm water down the pipe to eliminate any remaining sludge.
  • Kill any remaining adults outside the drain. Smack them with a fly swatter or spray them with an insecticidal spray and then clean the area thoroughly.

To keep drain flies from returning, keep drains clean and eliminate stagnant water (including water in potted plant saucers) in the home.


Do you have your own solutions for dealing with fruit flies, drain flies or fungus gnats? Let us know in the comments below or visit us on Facebook with your DIY insect eradication tips.

Also be sure to subscribe to our eNewsletter, which will deliver exclusive updates on our products as well as informative articles to keep your home bug-free.

Gnats, flies, no-see-ums, whatever you call them, they’re disproportionately annoying for something so darn tiny. Taking back your kitchen is easy though when you follow the right advice. Here’s how to banish these pests for good.

1. Look closer.

There may be teeny-tiny bugs flying around, but don’t assume they’re necessarily gnats. Fruit flies, drain flies and fungus gnats are three of the most common offenders, so you’ll need to get up close and personal to see what’s really going on. Fruit flies are brown with red eyes, drain flies have fuzzy, moth-like wings and fungus gnats are black with long legs, says Mike Goldstein, a Certified Pesticide Applicator for Woodstream.

From left to right: A fruit fly, drain fly and fungus gnat. Getty/Wikimedia Commons/Wikimedia Commons

Some context clues go a long way too. Fruit flies obviously like the kitchen, drain flies congregate around drains and fungus gnats like potted plants, Orkin entomologist Chelle Hartzer explains.

2. Stop bugs from eating by cleaning up.

The first line of defense when it comes to fly problems is eliminating the food source. So to keep fruit flies from feasting, stick produce in the fridge or inside bins as much as possible. You should also rinse fruits and veggies as soon as you get home from the store. “There may be some eggs or very, very tiny larvae,” Hartzer says. “By washing them and storing them sealed up, fruit flies can’t find that food source anymore.”

Drain flies have a much grosser meal of choice: bacteria, sewage and other gunk in your drain, garbage disposal or seldom-used toilet. Hartzer advises using a bottle of foaming drain cleaner to flush out the pipes, but the fix might take a little more work than that. Goldstein says an infestation can also signal a leak, so call a plumber if the problem’s persistent.

As for fungus gnats, exercise your green thumb. These pests love humidity and moisture, so ease up on the watering. Repotting houseplants in new soil also helps. “It’s the great for the plant and it’s great to reduce gnats,” Hartzer says.

3. Lay a trap.

While those preventative measures will stop gnats at the source, wanting to take some immediate action is totally understandable. And a good, old-fashioned vinegar trap certainly can’t hurt. (Get the how-to here.)

Aunt Fannie’s

The chemists in the Health, Beauty and Environmental Sciences Lab at the Good Housekeeping Institute also like Aunt Fannie’s FlyPunch ($9,, especially Senior Chemist Sabina Wizemann, who found that it worked better in her home than other homemade remedies she’s tried.

Safer Brand

Amazon reviewers also swear by these Sticky Stakes ($7,, which trap adult fungus gnats and other insects plaguing your houseplants. Again, these products won’t address the cause of the problem, but a multipronged approach probably isn’t a bad idea.

4. Don’t worry. They aren’t hurting anything.

While other species of gnats and flies — including the black gnat and black fly — do pose a disease risk, these three pests won’t do you any harm.

“Their mouth parts aren’t just designed to bite,” Hartzer says. “There’s not any diseases that actually transmit.” Rest easy that while finding flies in your drink is certainly annoying, there are some way worse pest problems you can have on your hands.

One of the most frustrating pests in many indoor gardens is the dreaded fungus gnat and its young, the fungus gnat larvae. These little buggers can absolutely destroy your plants if you’re not vigilant — and they can do it quickly.

The primary way that fungus gnats affect your plants is through their larvae. They lay eggs in your growing medium. Once they hatch, the larvae will attach to the roots of your plants and drain them of nutrients.

Although the larvae are the main negative actors, adult fungus gnats can carry disease, especially fungal diseases. These can be deadly on their own, but that’s not all. They also lay hundreds of eggs fast, which will devour plant roots!

It’s absolutely essential that you stop these pests before they can take hold, whether indoors or out. The last thing you need is for your plants to succumb to a horrible fate.

I’ll help you to overcome your fungus gnat woes, though. Let’s go into detail about fungus gnats and their larvae, and learn how to demolish them before they can take over!

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Organic Products To Eliminate Fungus Gnats and Larvae:

Hydrogen Peroxide
  • Can be used as a soil drench
  • Proxide solution kills fungus gnat larvae on contact
Check on Amazon →
Neem Oil
  • Effective soil drench to combat fungus gnat larvae
  • Spraying can keep adult gnats at bay
Check on Amazon →
  • Safe in hydroponics use
  • Also for greenhouses, gardens, and indoors
Check on Amazon →
Garden Safe Houseplant & Garden Insect Killer
  • Pyrethrin spray
  • Effective against fungus gnats and their larvae
Check on Amazon →

Environmental Products To Wipe Out Fungus Gnat Larvae:

Microbe-Lift BMC Fertilizer
  • Contains bacteria that will destroy fungus gnat larvae
  • Used when fertilizing
Check on Amazon →
Mosquito Bits
  • Contains bacteria that will destroy fungus gnat larvae
  • Used by sprinkling over the surface and watering them in
Check on Amazon →
Nema-Globe Pot Poppers
  • Contains beneficial nematodes that take out the fungus gnat larvae along with other soil-dwelling pests
Check on Amazon →
Dr. Pye’s Scanmask Beneficial Nematodes
  • Contains beneficial nematodes
  • For larger gardens or full yard coverage
Check on Amazon →

Products For Fungus Gnat Prevention:

21C Butterfly-Shaped Yellow Sticky Stakes
  • Attract and trap fungus gnats, fruit flies, and whiteflies
  • Controls infestation and breaks the breeding cycle
Check on Amazon →
TraPro Yellow Sticky Traps
  • Designed for flying plant pests
  • Made of non-toxic material
Check on Amazon →
Growstone GnatNix Fungus Gnat Control Mulch
  • Top dressing creates an effective physical barrier against fungus gnat
  • Non-toxic fungus gnat control
Check on Amazon →

Fungus Gnat Overview

An adult fungus gnat. Source: andybadger

Common Name(s) Fungus gnats
Scientific Name(s) Multiple, but the dangerous ones to plants are Sciaridae family spp.
Family Sciaridae
Origin Worldwide
Plants Affected Indoor/nursery/greenhouse plants, some outdoor plants. Particularly susceptible are plants such as carnations, African violets, geraniums, and poinsettias, but they can strike any weakened plant in the right conditions.
Common Remedies Hydrogen peroxide soil drenches, neem oil, other azadirachtins, pyrethrins, beneficial nematodes, Bacillus thurigiensis var. israelensis, sticky stakes/sticky traps, and mulches

Types of Fungus Gnat Larvae

There are six different families of insects which make up the broader category of fungus gnats. These six families include the Sciaridae, Mycetophilidae, Ditomyiidae, Bolitophilidae, Diadocidiidae, and Keroplatidae.

Most fungus gnat species are not harmful to our gardens, but the dangerous ones are in the Sciaridae family.

While adults don’t cause any lasting damage, the fungus gnat larvae of that family will move on to plant roots once their preferred foodstuff is gone. The larvae will chew holes in the roots and can cause yellowing, wilting, and even plant death in large numbers.

Not only do they damage roots, but the Sciaridae can spread disease. Since their preferred food is fungal growth, they can easily pick up spores from infected plants or soil and spread leaf spots, scabs, cankers, rot, and more.

Fungus gnat adults are often confused with mosquitos as they look similar in shape, but are much smaller. These tiny black gnats rarely get any larger than an eighth of an inch long.

The larvae themselves grow a bit larger than the adult gnats. Fungus gnat larvae have a black, shiny head with a white to clear body that can reach almost a quarter inch in length. They’re hard to locate because they tend to remain under the soil’s surface, out of view.

Life Cycle Of Fungus Gnats

A fungus gnat larva and some eggs. Source: myriorama

The life cycle of the fungus gnat is made up of four stages: egg, larvae, pupae, and adult.

The adult fungus gnat can lay about three hundred eggs in its short lifespan. They typically only live for about a week as adults, so they make the most of their time! Eggs are laid in rich and fertile, moist soil at the base of plants.

About four to six days after the eggs are laid, the larvae emerge. These larvae will be extremely tiny at first. During the roughly two-week period in which fungus gnat larvae are growing, they rapidly increase in size by eating their way through organic matter in the soil.

Once they’ve achieved maximum larval growth, there will be a 3-4 day pupal phase. The pupae will be hidden under the soil’s surface, and when the adult emerges, this cycle begins again.

Because of this quick life cycle, many generations of fungus gnat can be born in quick succession. In addition, many stages of the life cycle may be present at any given time. Not only do you need to get rid of the annoying gnats themselves, but you’ll need to deal with the larvae and find a way to sterilize the eggs.

Common Habitats For Fungus Gnat Larvae

Moist and rich soil, especially soil that tends to be a bit overly-damp, is perfect for fungus gnat larval development. Planting mixes that contain a heavy amount of peat moss or coconut coir will encourage them to move in and take up residence.

Avoid overwatering, especially during the cooler winter and spring months. Too much moisture will speed their development as it can cause roots to begin to decay, making a perfect food source.

Greenhouses stay warmer through the winter months than the outside garden, which makes them a perfect place for fungus gnats to try to overwinter. It’s especially risky as they typically have richer soils that are regularly watered, making for prime fungus gnat real estate.

In addition, people who have houseplants may find fungus gnats trying to invade their homes during the winter. Needless to say, that’s something that you absolutely want to stop as soon as possible!

What Do Fungus Gnat Larvae Eat?

A fungus gnat on a flower petal. Source: Arthur Chapman

While most fungus gnat larvae prefer decaying organic materials and fungal growths, any weakness or rot in plant roots can make them appealing targets. Similarly, if there’s a lack of organic material in the soil, the gnat larvae will feast on your plants instead.

Especially at risk to fungus gnat larvae are African violets, geraniums, poinsettias, and carnations. These four plants not only can develop root rot quickly, but they tend to live in a nearly-ideal soil type for the gnat larvae to colonize.

However, nearly any plant that is weak can succumb to fungus gnat larvae. Keeping your plants strong and healthy and free of decay will help protect them from this pest.

When Fungus Gnats Strike

A dark-winged fungus gnat. Source: John Tann

You’re most likely to get fungus gnat problems around the fall. As the weather cools, they seek out warmer temperatures, and your house or greenhouse are prime locations. Once they get to your soil and start laying eggs, they can damage or destroy your plants rapidly.

If you have plant problems and suspect it might be the work of fungus gnats, be on the lookout for yellow leaves that otherwise appear normal, or extremely slow growth. Both are symptoms of fungus gnat larvae in the soil.

If you spot either of these symptoms, or see adult flies buzzing around your garden, you need to react immediately.

Treat all your plants, not just the ones closest to the flies! It’s very hard to know if larvae are on plants that look alright, so you should cover your bases and treat everything. It’s better to be safe than sorry.

Plants recovering from fungus gnat problems still face the risk of disease problems. Fungus gnat larvae can spread fungus spores that are dropped by adult gnats to your plant’s roots, possibly causing a number of common plant diseases.

As a precaution, treat any affected plants and those in the area with fungicide a day or two after pesticide application. This ensures that if your plants did have contact with potentially dangerous disease spores, they shouldn’t contract the disease.

A root drench is more effective than spraying the plant’s foliage, as that’s where damage would be done.

How To Get Rid Of Fungus Gnat Larvae

An adult fungus gnat on a leaf. Source: epitree

If you use the prevention methods below, you may never see fungus gnats or their larvae. But if you do, here’s how to wipe them out!

Organic Fungus Gnat Control

Interestingly enough, a common household item is one of the top recommendations that I have for controlling these pests. Hydrogen peroxide (the standard 3% topical variety) can be used as a soil drench.

Mix one part peroxide with four parts water, and pour it through the soil at the root zone until it begins to come out of the base of the pot. The peroxide kills fungus gnat larvae on contact.

Neem oil is also an effective soil drench to combat fungus gnat larvae. Dilute the oil with water per manufacturer’s directions and directly drench the soil at the roots of the plant. You can also spray the upper portion of the plant to keep adult gnats at bay.

AzaMax is a higher-strength concentration of the azadirachtin which naturally occurs in neem oil. It’s safe in hydroponics use as well as in greenhouses, gardens, and indoors. Use it per manufacturer’s directions in the same way you would use neem oil.

Pyrethrin sprays are also effective against fungus gnats and their larvae. I recommend Garden Safe Houseplant & Garden Insect Killer.

To use pyrethrins, lightly mist all plant surfaces and the top of the soil. You don’t want the plants dripping wet, a thin mist will be enough.

If there’s fungus gnat larvae in the soil, spray the soil directly to thoroughly moisten the top, then avoid watering until the soil has dried to at least a 2″ depth.

Environmental Fungus Gnat Control

One particular form of bacteria will destroy fungus gnat larvae. Bacillus thurigiensis var. israelensis. It’s not in most commercial BT sprays, but it is available as part of a product called Microbe-Lift BMC Fertilizer.

Use this to fertilize with, and you should see a decline in your fungus gnat problems.

Another way to get this bacteria in your soil is by sprinkling Mosquito Bits over the surface and watering them in. You can use these both indoors and outdoors. They aren’t just for mosquito killing!

As they break down, they release Bacillus thurigiensis var. israelensis into your soil, where it can get to work killing larvae.

Beneficial nematodes can also play a major part in eradicating the fungus gnat larvae. You won’t be able to see these microscopic soil-dwellers, but they will take out the fungus gnat larvae along with hundreds of other soil-dwelling pests.

For people with indoor plants, you can add these nematodes to your soil with one of these Nema-Globe Pot Poppers. Larger garden or full yard coverage can be achieved using Dr. Pye’s Scanmask, which disperses the nematodes evenly with water.

Be aware that you cannot use beneficial nematodes at the same time as your hydrogen peroxide soil drench, as it will kill the nematodes! Wait for at least a couple weeks after the infestation and then add nematodes back into the soil.

Preventing Fungus Gnats

Inspect potential plants before buying them. Check at the base of the plant, gently looking through the soil to find signs of the clear or whitish fungus gnat larvae. Avoid any plants with visible adults around them.

To be doubly sure that new plants are pest-free, keep them quarantined from other plants for at least 2-3 weeks. This gives you plenty of time to spot newly-emerged adults, as well as establish control methods before they can spread.

Avoid overwatering your plants. Also, if fungus gnats or their larvae are in evidence, avoid watering until the soil has dried to at least 2″ deep.

Be sure to use sticky traps to find adult gnats. Since it only takes one gnat to lay potentially hundreds of eggs, you want to keep the adults at bay!

For indoor plants, these butterfly-shaped sticky stakes work well and are smaller in size (although they’ll still look big next to smaller plants). Outdoors, you can use these double-sided sticky traps.

Finally, mulching has good effect against fungus gnat infestation, as the mulch keeps the adults away from the soil. This prevents them from laying their eggs.

You can use a thick layer of a stone chip mulch over your soil, or opt for a product such as GnatNix.

Made from recycled glass, GnatNix prevents emerging adults from getting out of the soil. It also keeps adult fungus gnats from laying their eggs in the first place.

In the end, the best solution for fungus gnats is prevention. But there are many options you can take if they catch you unexpectedly. Have you ever fought against fungus gnat larvae or adults? What methods did you choose? Share your stories with us in the comments below!

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Kevin Espiritu
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How to Kill Fungus Gnats

  • Make sure the flies you see are really fungus gnats by trying the raw potato test. Place a piece of raw potato on the soil near an infested a plant. If these are fungus gnats, you will see them migrating to the potato within a few hours. If you lift the piece of potato, you should see the larvae.
  • Drench the soil with microbial insecticide, such as bacillus thuringiensis, more commonly called Bt. This is the most effective way to kill any fungus gnat larvae.
  • Allow the soil to dry out for a few days, so that the top 2 inches (5 centimeters) are really dry. The larvae of fungus gnats cannot survive in dry soil. However, they will remain dormant and begin their development once the soil is moist again. Water your plant with a mixture of one part hydrogen peroxide and four parts water. The solution will kill the larvae, but is harmless to your plant. Reapply the hydrogen peroxide solution once a week until you see that the fungus gnats are gone.
  • Place yellow sticky traps near the infested plant. These 3-by-5-inch (7.6-by-12.7-centimeter) adhesive-based traps attract and kill many, though not all. fungus gnats .

Identification & Appearance:

Fungus Gnats (Orfelia and Bradysia) are gray to black, mosquito-like insects that prefer warm, humid conditions. Due to this preference, fungus gnats are a prevalent pest in greenhouse and indoor growing settings as well as in outdoor potted plants. Common egg-laying sites include moist organic debris/potting soil, decaying wood (mulch), and ground cover plants. Adults measure 1/8 to 1/10 inches long (about the size of a common gnat) and they are distinguished from another greenhouse pest, the shore fly, by their long antennae. Fungus gnat larvae, the damaging life stage, are worm-like and clear to white in color. In large infestations the fungus gnat larvae leave slime trails on the growing medium’s surface similar to that of slugs & snails.

Fungus Gnat Life Cycle:

Fungus gnats mature through four life stages: egg, larva, pupa, and adult. Eggs are laid in damp media where they hatch within 3 days at 75°F. Hatched larvae feed on a variety of organic matter: decaying material in the media, fungi, or root hairs. Feeding occurs for about 10 days after which larvae pupate. Adults emerge after 4 days and reproduce shortly thereafter.

Damage Symptoms:

Symptoms of fungus gnat infestations are sudden wilting, poor growth, chlorosis (yellowing), and foliage loss. After hatching, fungus gnat larvae promptly begin feeding. Their feeding can cause significant root damage and severely inhibit nutrient uptake. Additionally, these feeding areas can become entrances for soil-borne diseases. The resulting damage commonly shows up as nutrient and/or water deficiency brought about by decreased root absorption. Adult fungus gnats do not damage plants; however, they can vector diseases like Pythium, Fusarium and Verticilium.

Controlling Fungus Gnats:

  • Monitor your growing area for presence of adult fungus gnats using yellow sticky traps. Adding Melissa oil to the traps has shown improved results in attracting fungus gnats.
  • Control soil moisture by using soil mixtures with proper drainage. Avoid overwatering to minimize breeding habitat.
  • Preventive and corrective applications of Bacillus thuringiensis israelensis products kills larvae before they can pupate. Aquabac, Mosquito Bits and Mosquito Beater WSP can all be used similarly to control and/or suppress fungus gnat populations.
  • Apply Nemattack, Sf to the growing media. The beneficial nematodes will parasitize existing fungus gnat larvae, slow their feeding and kill them.
  • S. scimitus (H. miles) helps break up the life cycle and eventually controls fungus gnat infestations by feeding on larvae and pupae. This small mite also feeds on thrips pupae and springtails.
  • Beauveria bassiana is a beneficial fungus that infects and kills a number of insect species. Applications should be made to growing media for fungus gnat control.

Quick Pest Reference Guide

Dealing with Flies

Flies! WA has such amazing weather and we all enjoy getting out into it but who would have thought that these tiny creatures could almost ruin a family barbecue, upset the dog and send us all fleeing inside out of their reach. How can we enjoy our backyards and our gardens when one hand is always waving these annoying pests away?

The best way to deal with these pests is to break the problem into sections and consider a few questions. What are we doing on our property that they find so attractive? What areas do we have that they use for breeding? How do we discourage them from even hanging around and how do we deal with those that do?

Flies remain dormant until their body temperature reaches approximately 18°C and only begin to search for food when the temperature is above 20°C which is of course is just about the time when we like to get outside also. Different fly species are attracted to different items. House flies like dairy, poultry and animal waste and garbage where as blow flies are attracted only to decaying meat. Flies search low for their food and like heat, light and low levels of wind. Their life cycle can take just 7 to 12 days to go from egg to adult.

Most gardeners agree that adding compost and animal manure to the garden is a terrific way to improve the soil’s structure, fertility and water-holding capacity. Many garden owners keep a compost bin in their backyard to reduce their household waste or bring in trailer loads of raw manure to spread across the garden beds. Often, in gardening, the smellier the manure, the better it is!

Of course, we all know that smelly things also bring in the flies. To them, animal manure and compost is no difference to humans at a sausage sizzle. Who can resist?

Uncovered compost heaps and raw manure allow flies to breed causing them to become a nuisance to the home and even to the neighbours and may even constitute an offence under the Health Act.

To reduce the opportunity for flies to breed, use enclosed compost tumblers or bins and ensure that the lid is always sealed. Don’t assume that just because an open compost heap is at the back of the block that the breeding flies won’t cause a problem to your outdoor barbecue area or house. Consider this pests name. Fly! They can travel long distances easily.

Avoid using raw manure on the garden, especially during the warmer fly breeding seasons. Compost the manure or purchase commercially composted manure, dig it through the soil and cover with a good layer of mulch to reduce access by the flies. Household scraps can be composted by burying it directly into the garden, ensuring that it is covered by at least 10cm of soil to prevent fly breeding.

Many backyards have bird aviaries or chicken pens. Most local councils allow home owners to keep poultry but with very strict environmental health conditions. One of which is that they should be regularly cleaned to avoid smell, rats, mice and flies.

Reducing the problem of flies in poultry pens and bird aviaries is very much down to the design of the enclosure itself as well as good hygiene practices. If the floor is constructed of a smooth, impervious material with a gradient of at least 1 in 50 it will be much easier to clean and will drain well, reducing smelly puddles of water and keeping the area dry. Ensure that the floor under perches and roost is covered with a good layer of sawdust to help the manure dry out and replace this regularly to prevent flies from breeding. Refresh the water daily.

Hang several fly catching traps outside of the chicken pens and replace the baits fortnightly. Spray the outside of sheds, perches and inner walls with an appropriate non-toxic surface spray and consider planting several wormwood, tansy or Lad’s Love around the pens as these attractive but tough plants are reputed to repel flies. Maintain these by simply cutting them down hard twice a year and watering them every now and then.

Better Pets and Gardens stock a variety of products that will help repel all pests, including flies, from the outdoor entertaining area.

One option is Coopex which is a water dispersible powder mixed with water and sprayed onto kennels, rubbish bins, walls, furniture, door and window frames and provides up to six weeks of control. It is very economical and safe and will control spiders, mosquitoes, flies and midges.

Outdoor foggers are an effective way of keeping flies and other pests away from outdoor entertaining and picnic sites. They are citronella based and are sprayed prior to entertaining to form a barrier to repel these annoying insects.

Natural insect deterrents such as sandalwood, eucalyptus and citronella are well suited to using around the outdoor entertaining area to repel flying insects. These are most effective when several are used to surround the area instead of using just placing one in the middle of the table.

Fly traps are a proven method of controlling flies. These are reusable plastic containers that contain a safe food based attractant which are harmless to animals and pesticide free. The bait attracts both house flies, blow flies and other species which all have different food sources. The bait is then placed about 40cm from ground level where flies tend to search for food and will attract them from approximately 20 metres. Once in, the flies are trapped and although they may still lay eggs, their larvae will not survive in the water.

Baited fly traps are best placed away from entertaining areas and entrances to the home to attract flies elsewhere and so that their smell doesn’t waft throughout eating areas.

Dogs can be terribly affected by flies. Preventing the flies from hanging around is just as important as protecting the dogs themselves. Dogs love to chew and doing this helps relieve their boredom and helps clean their teeth. During the warmer months, it may be a good idea to switch from giving fresh bones that attract flies to smoked clod bones or rawhide chews. They will enjoy these without the irritation of flies hanging around.

Wash the dog’s bedding as often as possible, especially if it gets soiled from the grease from bones or other food. Where possible, open the kennel lid weekly to allow it to dry out and clean out any food debris. Food bowls should be washed as soon as the dog has finished eating; avoid leaving it there to attract flies as well as ants.

Spray around the kennel, its roof and under beds with Coopex or other long acting surface spray. These last for several months and are effective at killing any flies that land on the surface. Spraying overhead beams or nearby walls will also help. Hang a fly trap above any areas that the dog spends time in though not near the back door – they can be quite smelly.

Animal manure attracts flies instantly. Collect all manure on a daily basis, especially during the warmer months when flies are breeding. The fly life cycle from egg to adult may be from 7 to 12 days so even a weekly pick up may not be sufficient to stop breeding.

Seal all manure into a plastic bag before disposing of it as the eggs may still hatch in the rubbish bin before it is collected.

Stable flies are common in most areas. They are biting flies that attack the most exposed area of a dog’s ear, generally the tip or the fold. They will seek out blood meals twice a day and can take up to three times their own weight in blood. Their bites are quite painful and continual exposure to them can cause redness and then lesions which the dog will make worse through scratching and rubbing, thereby attracting even more flies.

It is important to repel the flies as soon as they are evident and not to wait until the redness begins as then the problem becomes far more difficult to control. Non-aerosol insecticidal and repellent sprays are available at Better Pets and Gardens that are effective against flies and biting insects on dogs as well as other animals. These are lightly sprayed over the animal, avoiding the eyes, and can also be sprayed on the inner walls of kennels and animal sheds. In times of severe infestations, twice daily may be necessary.

Better Pets and Gardens now stocks a new product which attaches to the dog’s collar and emits an electromagnetic frequency to keep pets away. It is non-toxic, waterproof and lasts for up to four months. These are also effective against fleas and mosquitoes.

If lesions have already been caused from the biting stable flies, antiseptic creams that will also repel the flies are available and should be applied to the top to the ears, around the eyes and the base of the tail. If the wounds do not clear up and begin to improve quickly, a visit to the vet will be necessary.

Flies in the garden

I have been following this and like the comments even though it got off the subject for awhile. Just have to stick my nose I one last time. It’s about bugs and pesticides not Monsanto crops. Some years ago I read that bees are declining. I keep seeing others posting here but not educating as to how serious it really is. They are dying at a fast rate! The artical i came across states that global warming is nothing compaired to the scope of what will happen to mankind if the bees die off. Here I build an Eco friendly home and should have built bee hives to help save the world.LOL Fact is. Pesticides kill bees! Pesticides plain kill. That is the job they were made to do. No bees no more food unless we all go pollinate with our fingers and paint brushes. Something I have to personally do and I have bees lots of them. Bees pollinate our fruits ,veggies, grains etc… We all learned as children. GMO or not we need those bees! Spraying pesticides kills the bees faster! Really fast it seems these days. Natural selection people. West Nile might kill some of us. I am coming up so going to test my hide out next week been awhile. I have had dengue 2xs and still healthy as a horse. It hurts like being hit by a truck but most will live and go on. Next time it might kill me? Natural selection I guess will dictate my lifespan. I get Mosquitos bites every day. At this moment well I poke this out on my smart ph. My sons legs are covered in bites. I have citronella planted everywhere. Grease the kid up in skin so soft that cost 9 bucks a fill. No standing water anywhere. They exist. They are our preditors in a way. Only so much I can do really. My dog has torselo or bot fly larva developing from yes mosquito bites. Under control now I better mention. I have had these same maggots in me from ya mosquito bites. It happens its can be taken care of. Your number is up its up! Nothing you can do about it. Spraying isn’t going to help. These pesticides we ingest are not what will be killing us in 20 years because if you kill your bees at the rate we have been we all get to starve together. Fact is a fact We are over populated Nature has decided to thin us out. West Nile ,dengue fever ,yellow fever ,new twisted flues ,aids etc… Who would have guessed this west Nile would have spred so fast? Global warming is nothing GMO foods is crap , but I’m sure that loaf of white bread i bought is made of it. That can of tuna I bought might be toxic radiation? Spraying is going to only speed up something that is out of hand. Sorry for being so blunt Ignorance is the problem. Over population is a problem. Big $ in chem co is a problem. GM bugs Hell ya might slow it down. Read this link below It’s worth the time and very informative Really there are alternatives. There have been some great examples and tips above on how to keep them down and how not to get bit by the most dangerous animal on earth. Give blood and SAVE THE BEES please.

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