I have a question about getting rid of fungus gnats. I am growing indoors using a living organic soil mix. My plants are healthy at day 9, but I notice a few 1 or 2 fungus gnats flying around and I want to control them asap. If I water my plants with a 1 to 4 part mix of hydrogen peroxide, will it kill off the larva in the soil, and will it remove the beneficial bacteria from my soil as well? And is it safe for my seedlings? Lol. I’m a nube so forgive me.
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Diatomaceous earth. It is recommended and as close to “organic” without any pesticides. I have no clue about hydrogen peroxide use, I guess, dont. I’m not the go to guy for an exact solution and I have, or had the same problem. Yellowish flytrap strips work at catching the flying ones… I made a powder bottle out of an old flip top spice bottle. Squeeze it on the dirt lightly. One side effect is it can build up and watering will cause it to need to be reapplied because it will wash it away. I’m still waiting for my first treatment to show results. The last of the larva should be gone by harvest in a few weeks. The fly traps are covered with them, I got hundreds an haven’t had them up for a week.
I put down a layer of diatomaceous earth and let it sit there dry for like 55 hours. When I went in to water my plants yesterday, I only saw 1 fly stuck to the yellow cards. I ordered some nematodes from amazon, hopefully they show up alive and once my plants are a bit bigger, I’m going to top the soil with silica sand. I was watering to often, not letting the top inch of soil dry out before I watered again. Lesson learned, so I hope better watering practices,the DE, and the sand will eradicate these punks. Thank you for your reply.
I used plain old sand. About 1/2" on top of the soil worked for me. Need to make sure of full coverage around edges etc. Babys hatch and cant make it up through the sand. Its breaks the cycle.
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right on!
Mosquito Bits works great for fungus gnats, sprinkle on top of soil and water, will kill the gnat larvae in the soil, breaking their life cycle. Can also use the DE mentioned above to help eradicate the soil crawlers and some yellow sticky traps for the flyers.
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Fly tape is what I keep in my tent and the beginning of the grow I put some beneficial nematodes (microscopic) in the soil as we were having a plague of cutworm moths and I kept finding them in the tent. My bad, when I opened it they flew in and were hard to see/know there at times. I wonder if the nematodes would take care of the gnats? I used to think fly tape was a bit low class, mainly because I grew up low class and fly tape was a big deal, that and ALL of us were armed with fly swatters. But it is worth the $3.00 for a four pack. 
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I read that those yellow cards work more than fly tape because the fungus gnats ate apparently attracted to the color yellow.
It’s TRUE. I got a 30 pack of larger double sided yellow sticky traps off amazon for under 10 bucks. I cut them into quarters and stick a popsicle stick to one side and plant it in the pot. Any strays dont live long. I followed up with those after the sand stopped 99%. I had an infestation lol.
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If I have a fresh dry layer of diatomaceous earth on the top of my soil. How do I apply beneficial nematodes? If I just pour it through the DE wont they be killed the same way the fungus gnat larvae get killed?
H2o2 will kill off beneficial bacteria, fungi, delicate root hairs, and possibly the fungus gnats.
BTi, the stuff in mosquito bits or available on eBay in a pure form, will work very well and not harm beneficials.
These beneficial nematodes are also supposed to do the trick without damage. I haven’t used them, but I trust the reviews.
https://www.amazon.com/BioLogic-Scanmask-Beneficial-Nematodes-Steinernema/dp/B00BWRNE3A
Last year I had a major infestation of fungus gnats with an indoor tomato grow. I reduced the numbers with mosquito bits and yellow sticky traps but failed to wipe them out.
About three weeks ago I saw a couple near the weed. I panicked because my project might be vetoed.
I set some sticky traps. I also blended in some mosquito bits left over from last year in the top layer of the soil. I purchased some D.E. and sprinkled it on the top of the soil.
Originally I bought the bits because I thought they were cheaper than the dunks based on weight. Now I am not so sure. A lot of weight in the bits comes from the corn kernel centered in the bit.
I ordered some dunks for soaking in water to be applied when I water. I’ll save the bits for blending in the soil.
The sticky traps proved useful for identifying their presence. I ended up catching three so I knew I had a few more that had escaped me and my hand held vac.
Now it has been two weeks and I haven’t seen any and nothing on the traps so I think/hope knock on wood I wiped them out this time.
Hydrogen peroxide has literally no effect on the plants other than helping bring oxygen to the roots. Recommended you not use too much but it’s actually a little useful when it comes to controlling certain insects and mold.
I launched a three-pronged attack on fungus gnats during my first grow. I put mosquito bits in a sprayer bottle with some warm water and neem oil and let it sit overnight. I sprayed the surface of the soil until it soaked in a bit. I hung an “insect guard” repellant strip in the tent. The gnats were gone in a day. I used yellow sticky cards to monitor the tent for any bugs for the rest of the grow. Do Not use the Insect guard strip if you are living in the same room as your grow. Follow the directions carefully.