How to Get Rid of Fungus Gnats

Fungus Gnats? Small, pest flies, two or three millimeters long, like many mosquitoes. They don’t bite, or sting but they are annoying to both you and your plants. From that point, if you intend to find a way on how to get rid of fungus gnats, don’t miss this article.

Why do we have to kill fungus gnats?

Instead, they love to crawl and creep around on plants and growing media. They fly around stupidly, getting in your face, buzzing from place to place, slowing and seemingly without purpose, but somehow very irritating at the same time. Sometimes, they even cause allergies.

There are tons of varieties of fungus gnats, but most likely you have unwelcome guests from either the Mycetophiliadae or Sciuridae family. Some growers confuse them with winged root aphids, which are better fliers, with a rounder broader body. And they are more attracted to your grow lights.

Sure, the adult gnats don’t do any damage, but they love to fly around your eyes, and up your nose and seems to have a sixth sense of when you have both your hands full, and you can’t swat at them.

However, the serious matter is their larvae – hatched from tiny eggs laid by the female adults in moist growing media. It causes all the issues, especially to young plants.

The fungus gnats larvae primarily feed on organic material, algae, and soil fungus. But in increasing numbers, that necessitates a broader diet, including roots, and plant stem tissue.

Why do we have to kill fungus gnats

Image source: Fine Gardening

Yes, the nipple on your plants’ root, which in turns, creates wounds. It opens up the gateway to secondary infections from the likes of Pythium, Phytophthora, and Fusarium. Seedlings and younger plants can die! Older plants could stop growing! Leaves will discolor and wilt, and nutrient and water uptake will slow.

From that point, let’s neutralize some gnats!

How to get rid of fungus gnats

As with all pests, you must understand their lifecycle, and disrupt it, preferably, at multiple stages at once.


Ignored fungus gnats will breed uncontrollably, and a few weeks after spotting a handful of fungus gnats, you will have a major infestation on your hand.

Fungus gnats can hitch a ride into your grow room on your clothes, or cuttings accepted from friends, through gaps between doors and walls, in the soil, compost, and soilless potting mixes.

Once introduced, they seek out moisture and humidity. Top feeding your plants too often creates ideal breeding conditions, that is, moist surface growing media.

Consider irrigating your pots from below and allowing your plants to wick up moisture instead. At the very least, ease off the irritations, and let your growing media dry out more between waterings.

Now, adult fungus gnats enjoy a brief moment of sexy time together, and then the females lay their eggs in your growing media. Sometimes, it is also in the algae that form at the top of stone wool blocks.

Try using block covers, or you can fashion some yourself with little squares of correx, or plastic sheeting to stop the algae from forming in the first place. And this is also to form a physical barrier against the gnats.

How to kill

Two-pronged approach

Two-pronged approach

Image source: How To Get Rid Of Gnats

I recommend a two-pronged approach. Target adults with foliar sprays and traps, and larvae with nematodes, mites, or biological larvicides.

Now, you should always have some yellow sticky traps in your store cupboard, even better, already in your garden.

Sticky yellow traps are a handy monitor for pests, not just a creative measure. Peel the protective wrapper from both sides, and lay them on the tops of your pots, rather than hanging in the air.

By that way, they can catch emerging adults.

Ask for predatory insects

Call your local grow store and ask them if they have any predatory insects in stock. Do this right now because chances are they may have to order them which can take a few days.

For the adults, try something like Azamax, a botanical insecticide, miticide, and nematicide. Use a foliar spray for a few days before sending in any beneficial insects. Make up a medium strength solution: one fluid per gallon and foliar apply immediately.

Work fast, wear a respirator mask, and get out of there. As for killing the babies, if you have cuttings and seedlings in blocks, you can dip them into a bacterial larvicide containing Bacillus Thuringiensis Israelensis, or BTI. For example, Gnatrol WDG or Mosquito Dunks.

Remember, if using multiple combat methods, it’s important to know that they are fully compatible with one another. It’s because some products will kill your predators.

Ask for predatory insects

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Use specific product combination

Also, ask your grow store for advice on specific product combination.

Parasitizing nematodes are incredibly effective against fungus gnat larvae. Besides, it can decimate fungus gnat number in days, while causing no harm whatsoever to your plants.

The nematode species of choice for this application is Steinernema Feltiae. You can buy them in little packets. It looks like dust, but lurking within are millions of tiny little beneficial nematodes. Note the use-by date on the packet.

The nematode enters the body openings in many types of soil larvae and uses them to breed. This kills the larvae in the process. Excellent!

Fill a watering can with dechlorinated water. Then, add the nematodes and stir. Apply carefully and evenly to the surface of your growing media.

I redirect the drain pipe of my ebb and flow table to catch the runoff so I can reapply to other plants. They won’t survive long sat in water so use it up right away.

Hypoaspis miles

Hypoaspis miles

Image source: Planet Natural

Hypoaspis miles: a tiny, predatory mite, invisible to the naked eye, has recently been reclassified with an even catchier name – Stratiolaelaps scimitus.

Many growers deploy these mites a preventative measure as they can last long up to 70 days without food. Thus, why not just let them hang out. Usually, they come prepackaged in sachets or tubes of peat and vermiculite.

A 34 oz container of Stratiolaelaps scimitus retails for around 40 dollars and can treat between 100 and 200 3-gallon pots. Thus, it’s not going to break the bank.

Sprinkle it onto the surface of your growing media, and you’ve done.

Diatomaceous earth

If you can’t get ahold of predatory mites, then try a top dressing with diatomaceous earth, Growstone Gnat Nix or Gnat Block by Flying Skull. I use Diahydro, which is fairly chunky.

Try to get the powderiest stuff at the bottom of the bag. Diatomaceous earth is fine for us to handle. However, to a newly-born gnat, it’s like crawling over razor wire. It’s only effective when it’s dry so try not to get it wet.

Once again, flooding from the bottom is the preferred method of feeding. Some growers use neem cake in their soil mix, or neem seed meal as both as soil enricher, and a preventive measure against fungus gnats. If you are growing in NFT grow tanks, then be aware that capillary matting is also a favorite for fungus gnats. Thus, be sure to secure the tank covers well to avoid gaps.

Finally, don’t forget to secure your air inputs with intake filters or bug screens, and always keep your grow room clean and tidy. If you’ve been gardening outdoors, take a shower, and change your clothes, and footwear before entering your indoor garden.

Above are all my tips and tricks on how to get rid of fungus gnats. Hope that they are useful and if you have methods of fungus gnats control, or techniques for complete annihilation that I’ve failed to mention, then please don’t forget to share them with us.

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