How to kill fungus gnats larvae

Hey guys was wanting to know how to kill fungus gnat larvae in the soil before using it. FYI its fox farms ocean forrest. Thanks in advance!


I’ve heard of people using this and the yellow sticky cards. I know @Paranorman uses the cards. I need to get some myself. I’ve never used the linked product.

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…a great thing and maybe the best thing about the cards is they let you know how severe the infestation is

I put a big fan on the floor and I don’t have them anymore, they can’t fly and that quickly breaks their cycle, and with the fans I use I don’t even think they can walk, I think it just blows them in a corner (and not in a good way)

@Swan1234 I agree I’ve come to the conclusion that they come out of the soil as well (just my opinion)


Let it bake in the sun, that should do the trick lol.

Thanks for all the advice ill have to get me some of those cards and air ventilation will be no problem. I’ll probably end up putting it in a plastic tub with a lid and let it bake in sun.

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@Swan1234 I just went to an episode of fungus gnat and I get rid of the larvae with slices of potato a trick that @garrigan62 gave me and it worked fantastic, just let them 4-5 days and they will be attract to the slices, just dispose of those in a tight seal bag. Repeat if necessary. If you want to know more about fungus gnat you may want to consult my topic on my personnal experience :wink::innocent: heres the link


Growstone Gnat Nix! Fungus Gnat Control, 9-Liter

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Works really good applied 24hrs placed sticky card back in tent nothing

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Hydroponics store guy Raves about those stones ! …nematodes work well too

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I’m surprised no one mentioned one of our favorites here at ILGM as it is all natural and the food grade stuff is totally safe for humans and pets, Diatomaceous Earth.

Diatomaceous Earth is kind of like the old fashioned clay kitty litter, except it is food grade and the kitty litter clay stuff comes from saltwater beds and is not good for plants or people, diatomaceous earth comes from fossilized hard shelled algae and the garden and food grade stuff comes from fresh water beds. When used as an insect dust, for insects it is like crawling over broken glass but is harmless to pets and humans as long as you are not inhaling large quantities of the airborne dust, and in fact it is actually good for you as a mineral supplement when eaten or added in foods in small quantities. The food grade stuff can be found as a food additive in health food stores and is also usually easily found at garden supply outlets like home depot.

Happy growing,



I got “molested” by fungus knats once,…haha, they reproduced, I tried to spray a water based solution, over watered my plants, kept spraying,…then I read about various things, but I quickly used some perlite and coated the top of the pots with a thick layer of perlite, mainly cause I had a large bag of the stuff left. What happened was, having been told of this, it interrupted their ability to reproduce well, I mean, oh sure, they kept on living for awhile, but it works. But now, I have some knat nix, but man, that time I had my max allowable number of plants, …I was thinking it would be best to just wipe out all the plants instead of continuing on…I think to this day over a year later that somehow it came in the soil I was using, some stuff I had used as extra, not foxfarm, just some off brand, that is when the problem started like the larvae were already in the soil itself…

Yep @MacGyverStoner when it is what cured my pest problems i now mix a couple of quarts in my soil to start and work a little extra into the surface. At a month old now and just starting 1 time a week neem oil spray treatment till transition to flower starts just as a prevention.


Yes Sir I mixed it in with the stones

I’ve also recently read about a good top dressing of worm casts can help because of the beneficial nematodes it contains will feed on the larvae.

Only read it. Experimenting with it now, as well as incorporating milk …

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Has anyone tried hydrogen peroxide mixed in water ? GW