Gnat/fruitflies and how to get rid of them

I’m having a severe gnat/fruitfly issue with this grow, it’s an indoor tent grow and the plants are in organic soil.I keep the temp at 75 and the humidity is at 68%. I’ve never had this issue before and am struggling with how to get rid of them and not harm my plants that are getting close to flowering. Please any advice or tips are greatly appreciated.

diotomacious earth sprinkled on top will kill bugs.
uncle jacks bug killer works well


Sticky pads or tape for the flys. And you will need to let the soil dry out the kill the larvae.


Durring extream infestation i place a chunk of potato on the soil, the larva will migrate to the potato(iv read that they will enter and eat the potato but that has never happened) i usualy find large amounts of larvae under it. (This may seem gross) i smash up the larvae with the potato into the dirt and then place it in a different location. I will continue to do this untill ther is nolonger and larvae

And yet another answer…
BTi. It’s the active component in mosquito bits, also available as a pure powder on eBay.

There’s also a beneficial nematode product called “scanmask”. I haven’t tried it, but assume it’s as good as the BTi.

Fungus gnats love wet soil. So overwatering will bring them out of nowhere. If you’re using a living soil and keeping it moist it’s hard to keep those little critters from showing up.


What @Drinkslinger said…Works great


Thank you! I am going to try this, do I just sprinkle it on top of the soil?

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Instructions on back.
You can add them to your water for a while and strain out the bits…just corn cob impregnated with bacteria…or mix a couple spoonfuls into the top couple inches of soil.

My container is over three years old and still works fine. It lasts a long time and goes a long way.


Had a very bad infestation a few years ago… This time used some other remedies and have had very good luck.

Definitely want to break the gnat life cycle which takes a bit.

  1. Dry the soil as much as possible then water throughly with following solution:
    1 cup 3% or higher hydrogen peroxide to 3 cups distilled water. The peroxide kills the larvae and breaks down into water and oxygen… Which in turn helps the oxygen at the roots helping the plant.
  2. Let it dry… Fans on the soil… Heat… Only water when absolutely necessary and only around the plant stem to water the root ball leaving the rest to dry.
  3. Hang fly paper strips.
  4. Use the yellow sticky paper (the gnats are attracted to the yellow) fans help blowing flying gnats to the sticky paper and fly paper.

5…about to…add nematodes… Must wait one week after the peroxide or nutrients feeding… Soil should be moistened first before watering down with water/nematode mixture. They are tiny round worms that ultimately kill and control many pests… Are safe for humans, plants and animals… Get the right nematodes… There are bad ones… Not sure which off hand.

That helped me… You could also use the food grade diotomacious earth… the sharp edges cut the larvae and kill them. I haven’t tried it this time around.

I have read others that have used… After drying out…
A nice layer of playground sand on top of the soil.

But the main things… Dry the top inch or 2 of soil. Only water when needed… Don’t water all the top soil just around the base of stem… Let dry…

I hope this helps… They can drive you nuts.

One other thing… Discovered tonight.

I have an evaporation humidifier… A cheap Walgreens brand… Went to add water to the reservoir an found it to be a breeding ground for fungus gnats…need to get a new humidifier now…researching. Added peroxide to the reservoir water to stop that… But the evaporation wick filter is… It seems good for gnats bad for grow tent at this point.