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Fungus Gnat Larvae Killa! can't believe it works!


New Member
Damn...that'll get rid of fungus gnats lol


Member of the Month: July 2012, July 2014 - Nug of the Month: July 2012


Grow Journal of the Month: March 2017
Ok, so I couldn't find any sticky traps..only fly strips which I effin hate....However I've done some reading on Hot Shot No Pest Strips...people seem to argue over it because it not organic, but hey we can't stop the sun from setting....if used CORRECTLY they work wonders on fungus gnats...I treated the soil with some H2O2 water 1:3( 1qt per gallon) and it bubbled all the lil crawlers and may have killed my basil because the soil foamed up higher than the seedlings lol oops...careful, it's more effective than I thought ;)

I will post my results in a few days :Namaste:

The H2O2 will kill off a good percentage of your micro herd. I would never pest strips and have only had fair success with organic drenches. The very best gnat problem treatment for me is always beneficial nematodes...the best one for gnats is Steinernema feltiae. Gnats flourish in the top 3" or so of media, and this nematode is best for that area.
When you start giving advice about diluting peroxide it would help if you gave the percentage of the original. Talking about a leak in a Soviet sub is of little use to someone talking about killing fungus gnats as you will never bring that high of a concentration of H2O2 into your home (or even be able to purchase it). Something you should also know about peroxide is it is kept in dark containers because the sun degrades it and it will release the extra atom of O2 and you will be left with plain water and some pressure in your clear container so do not mix and let it sit, use it immediately. Peroxide will attack ANY and ALL organic material. Peroxide as it decomposes creates a lot of heat which will destroy anything living if used in too strong of a concentration. I can see how a dilute amount may help to bring O2 to the roots but I am sure many have damaged the roots by using it at too high of a concentration. There are other remedies for killing the gnats, I wouldn't introduce one with so much downside or recommend to someone else to do so


Well-Known Member

fungas gnats easy to get rid of in soil. Put a 1/4 inch layer of sand on top of soil and gnats are gone. It smothers larva and prevents them from being able to come out. easy fix. But NEVER use gognat. That stuff will darn near kill your plants/


New Member
I have been having the same problem.
I have tried many common organic recommended solutions... nothing works.
My thought is to get rid of the main reason they are there to begin with first..
Use a fungicide to remove fungus and algae which is what they feed off of and attracts them.
Perhaps then they will go away or will reduce the numbers significantly making the other solutions more effective.
I tried an Azamax soil drench a couple times as well as a BT drench and it doesn't seem to work. I have even transplanted in fresh soiland bathed the roots in a light soap water then rinsed and replanted.
I have read somewhere about placing a cap around the top of the soil. This way any larva below, when hatched they can't get back out and the gnats on top can't get into the soil to lay their eggs. That sounded like something that could work, but I can't believe they still can't get through the edges somehow. Maybe if you caulked around the edges (haha). But you will have to remove the cap to water.

Another method is to add diatomaceous earth. You can add to the water for soil drench as well as spray in
bottle (But it does clog your gun). It destroys the skeletal composition of the insects when they come in contact with the dry earth apparently. It can be a great resource.


Well-Known Member
Hey Debudman, and anyone else reading...

I'm currently dealing with fungus gnats in my current grow. I've been catching a fair number of adults on yellow sticky traps but haven't visually checked the coco medium for larvae, though I probably should. Lately I've been covering the coco with diatomaceous earth with the hopes that will kill the larvae. Will that take care of larvae that are lodged a couple of inches down from the surface though? Also, you say I can mix DE into my nute mix. That sounds good. Any idea how much I should add per gallon, for instance? Is it still effective in killing gnats when wet?

Next time I'm going to do what Icemud mentioned and mix DE and BTi into my Coco before adding my seedlings.

If I want to do an H2O2 drench, I've read that the proportions with 3% H2O2 should be 1 part H2O2 to 4 parts H2O, so that's 20% H2O2. If I have 34% H2O2, which is roughly 10 times stronger than 3%, does this mean the proportion should be more like 2% H2O2 (instead of 20%) and 98% water then? I don't want to mix up and apply the solution it without knowing I'm using a safe concentration of H2O2 for the plants.

I'm also intrigued by using a sand layer at the top. Has anyone done this with good results? If there are already larvae lurking in the medium, how does the layer on top impact them exactly? My assumption is they would still be able to eat through roots, but maybe they wouldn't be able to come up to the surface and then die? Is that the idea?



Well-Known Member
I'm telling you put the sand on them .problem gone as soon as you do it. instant fix. promise.

Hey bozzo420. I did put a layer of dry sand over the coco but it ended up getting swished around a fair amount after watering so much of the coco became visible again.

Do you keep adding sand each time or is there a way to keep the sand in place throughout waterings? :thanks:
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