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Frickin' Fungus Gnats!


Well-Known Member
They're all over. I know it's from too much watering, but I need to get rid of them. Quick.
One plant shows already signs of damage which I think is from fungus gnats.

I already put yellow sticky traps up, but now I need something to kill the larvae.

I am in Spain and I was looking for biological products based on "Bacterium Thurengiensis Isrealensis" but I can't find any of such products. The irony is that I have already a "Bacterium Thurengiensis" product but this seems only for caterpillars.

So I searched a little more, and people say Vermiculite on the top of the soil would be good. (Along with possibly Neem oil). I have no problem getting this.

Anyone used Vermiculite on top of their soil/pots to get rid of the fungus gnats? Did it work?


New Member
Hi Flexy123,

I've used both vermiculite or sand on top of my soil and both seem to cut down on the gnats somewhat. Problem was it didn't treat below the soil surface and after a while the gnats were back. I think it's actually the larvae that do the damage.

Neem oil will work to treat the larvae, but you'll have to soak them really thoroughly, which in a situation of previous overwatering isn't the ideal solution. I wouldn't hesitate to use the Bacterium Thurengiensis product you have since it's a just a bacteria. It will either kill the fungus gnat larvae or it won't, but it certainly won't hurt your plants. Again though, the only way I've seen to use this product is in liquid form - thus again introducing wet to an already too wet environment.

Do you have access to diamotaceous earth? That was how I finally got on top the little buggers. I spread it all over the top of the soil of each container. I found that I had to reapply after watering (when if was finally time to resume watering), but that was the only downside I experienced.

Good luck, be well and happy growing!


Well-Known Member
I am not sure about D.E., people say it's worthless if it's moist?
Sand I would actually have, problem here is that people said it can block water from getting to the roots.
I think I might just get a 10L bag of vermiculite.

While I have those gnats everywhere, the plant which was affected, I scraped off the upper layer of soil (where the eggs/larvae are) and repotted it for now. Seriously I see those tiny black things jumping around in every pot ;(


New Member
Yes, D.E. would need to be reapplied after watering as it is worthless when wet. I did not have any issue with sand blocking water getting the root zone. I just watered a little slower as it does take minute for the water pass through the sand.

I hope between the scraping off a layer of soil and whatever other remedy you choose you get them under control. I've always understood that the larvae cause damage to the plants by feeding on the root structure. Which leaves me wondering if they would still be hanging out in the soil you scraped off. Anyway, good luck getting rid of them! They certainly can be a PITA.


Well-Known Member
i found, that when i was decloring my water, in five gallon buckets, with lid off, the gnats were like lemmings. dove in and drown themselves. i had them, when using organic potting soil, good stuff, gardener n bloom. also, you can add some cedar oil (gognats) to the drink. finally, i got rid of them, by moving to soilless!! its a miricle!! no more gnats. i kind of like also, knowing the girls get only wnat i give them. lately, thats been gat guano, and dynagro. microbrew, and kangaroots. ph 6.5. anyway. gnats are not that harmfull. an irritant, mostly. put water out, near the plants. they will fly in. my buckets are white, i think this helps. perhaps yellow ones, would attract them even more?


Well-Known Member
Howdy, this is all natural plant oil extracts that are non toxic to pets or people and used by many on this site...

SNS-203â„¢ Pesticide Soil Drench/Foliage Spray Concentrate

SNS-203â„¢ Concentrated Natural Pesticide Soil Drench and Foliage Spray is made up of pure Rosemary and Clove botanical extracts. The botanicals are all food grade GRAS (generally recognized as safe) materials. SNS-203â„¢ Concentrated Natural Pesticide Soil Drench is exempt from EPA registration under minimum risk pesticides exempted under FIFRA section 25(b). SNS-203â„¢ Kills and Repels Fungus Gnats, Root Aphids, Thrips, Shore Flies and White Flies.

How It Works
High moisture levels in soils and around pots encourage the development of fungus gnats, shore flies and other pests.
 Fungus gnats will feed on fungi and decaying organic material in the soil. If a fungal food source is not readily available, fungus gnats may feed directly on plants. During the propagation of cuttings, fungus gnats may feed upon the callus. This may slow down or completely inhibit rooting. They can also damage the roots as they feed upon seedlings and potted plants. On many thick and succulent stemmed plants, larvae may tunnel into stems and cause plants to wilt and die. Larval feeding upon young roots encourages the development of root and stem rots such as Pythium. When this occurs, plants will be stunted with reduced growth and leaf drop.
 Shore flies feed upon algae and do not directly feed upon plants. However, their frass (droppings) on plants, in addition to their presence, may be objectionable to customers and may carry other diseases.
 SNS-203â„¢ Concentrated Natural Pesticide Soil Drench active ingredients, attack fungus and algae and cause the pests to dehydrate their body fluids and dry up.
 When used as a foliage spray SNS-203â„¢ will control and eliminate Greenhouse Thrips, Fungus Gnats, Root Aphids, White Flies and Shore Flies.
Our Product has been tested in our lab on delicate new growth, clones, cuttings, tomatoes, roses and other plants.

SNS-203â„¢ Concentrated Natural Pesticide Soil Drench can be used on a wide variety of plants, vegetables, and even trees. When applying the product take caution not to apply to any buds on the plant, in doing so this could result in burning the buds. SNS-203â„¢ can be applied to soil or sprayed on fruits, vegetables, and plants varying from; apples, apricots, beets, broccoli, cabbage, carrots, cauliflower, celery, cherries, chives, corn, cucumbers, peppers, tomatoes, parsley, fuchsia, roses, flowers, houseplants, etc. SNS-203â„¢ Concentrated Natural Pesticide Soil Drench is fully bio-degradable and is non-toxic to animals.

Directions for use:
Soil Drench:
Mix 4-8 TBSP (2-4oz) of concentrate to 1 gallon of water. Thoroughly drench affected and surrounding area.
Foliar Spray: Mix 4-12 TBSP (2-6oz) of concentrate to 1 gallon of water. Spray Foliage to point of runoff.
Repeat 2-3 times as necessary. Do not mix with other chemicals or fertilizers.

Directions for Use in Hydroponics:
If you can remove plant from system
- Remove plant and place in 5 gallon bucket.
- Pour solution over top of the root system down and drain into the bucket.
- Let sit for 5-10 minutes.
- Rinse with water and return plant to system.
- Apply 2-5 times every 2-3 days as needed, depending upon infestation.
- You may reuse the solution in the bucket, simply strain unwanted pests and set aside. The product is good for 2 years after expiration date marked on bottle. Keep out of sun and away from extreme heat.
If you cannot remove plant from system
- Pour solution over the top of the root system down and let it drain into the system.
- Use on each individual plant, pouring over top of root system.
- Apply 2-5 times every 2-3 days as needed, depending upon infestation.
- Make sure to flush system appropriately after use. SNS-203â„¢ should not be left in a reservoir.
CAUTION: Do not use with other products. 

Active Ingredients

Clove Oil1.5%

Rosemary Oil0.53%

Polyglyceryl Oleate0.6%

Lauric Acid0.11%

Water Balance to100%



OEF Vet 11B

New Member
I put less than a table spoon of diatomaceous earth in ny sprayer bottle and spray the tops of the soils it wipes the larva out and I always see immediate results. After adding more air movement I have yet to see gnats (knock on wood.) If your grow room is large a fan above the canopy and a fan below will help rid of them. This doesn't allow them to land to lay more larva. I've never had to use anything other than d.e

Major PITA

Member of the Month: Oct 2015, June 2016
BT won't do anything.


New Member
Gnats came in a bag of FF soil from my local grow shop. I used Gnatrol from ebay and got rid of them. Whenever I use more soil I water with 1 tsp per gallon and have not seen a single bug in months. Yellow stick traps after a few applications will confirm the elimination, suggest new traps after using, but hold of a few days to let it work. For first use I would use every watering for about 2 weeks to let the eggs open and larvae be eaten by the Gnatrol.
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