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Fungus gnat larvae in soil

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#1 Baphom3t



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Posted 09 April 2016 - 01:25 PM

I am very familiar with these little bastards and had to isolate some now dead seedlings from the rest of the ones I have going and I don't want them to screw up any future fungus grows.......but, this is directed to my gardening plants.
I've gotten some soil that has these little douchebags in there. I know about the yellow sticky stuff and how to do it DIY style but that is for the adults more than the larvae, I know about letting the soil dry out to kill out the larvae but the seedlings and less established plants suffer greatly from the lack of water.
I'm wanting to stay as organic as possible.......
What is your guy's thoughts and experiences with the following solutions I have found to deal with these little scumbags.

Gnatrol ----->
Nematodes ----->

Hypoaspis miles ------> http://www.planetnat...tor-entomite-m/


I've done a ass load of research on this and there are even more solutions but I am curious as to what the community thinks and would recommend to kill these little bastards?
Any other recommendations to get rid of the larvae are welcome as well.

Edited by Baphom3t, 09 April 2016 - 01:27 PM.

#2 Myc


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Posted 09 April 2016 - 02:10 PM

Food-Grade diatomaceous earth. The food-grade variety has a smaller particulate size which is more effective at damaging small organisms like larvae.


The non-food-grade variety has larger particles - the smaller organisms can move around them un-damaged.

Introducing diatomaceous earth to your grow is like pouring ground glass all over the playground. Not toxic, but you can bleed to death from a thousand cuts. By this method of abrasion, the organisms lose all of their precious moisture and must either relocate or perish.

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#3 Baphom3t



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Posted 09 April 2016 - 02:45 PM

I've used that in the past and the results were no go.
Maybe I didn't use enough....but I don't know
It works fine until you water and then it becomes less effective from my experience, or until the potting soil dries out which then it's effective again.....which there again is detrimental to seedlings and less established plants
I've used it to get rid of fleas also to no avail as well......I still have a butt load of it so I may try that in case the other methods I am coming across fail.
I've talked with some folks at a couple hydroponics stores in my city and they are happy with the nematodes and of them had something else that they swear by but I can't remember the name of it......dunno......I've also thought of putting the soil under high heat or extreme cold.
One of the nurseries in my city also is facing the same problem and they were looking for a solution so this will be a interesting ride.

#4 dead_diver


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Posted 09 April 2016 - 05:49 PM

Neem oil has worked for me. Also nuke or bake soil in the oven before use if you don't  have  too  much .

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#5 Baphom3t



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Posted 10 April 2016 - 09:35 AM

I've used neem oil in the past with no luck. I have about a 35 pound bag left........I'm thinking I can do it in sections and let cool for 24 - 48 hrs and then use to plant.
I'm curious as to how much to use and for how long per section........I have a few 72 seedling trays that I'm wanting to do.
Also this soil has miracle gro in it which is meh........some of the newer soil I have just got is organic with no additives and I plan on using fish emulsion on.
So what temp and for how long, along with the amount would I put the contam soil in the oven and or microwave for?

Edited by Baphom3t, 10 April 2016 - 09:37 AM.

#6 dead_diver


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Posted 10 April 2016 - 10:57 AM

If it has Miracle it Grows in it I wouldn't use it.
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#7 PsyBearknot



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Posted 13 April 2016 - 07:06 AM

I've crumbled mosquito dunks on top of the soil and worked that in a little and then watered with mosquito dunk water.

But now that I think of it, that breaks the food cycle by starving the adults not working on the babys.

#8 JanSteen



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Posted 10 May 2016 - 04:16 PM

King oyster mycelium eats gnats for breakfast. It can form sense-activated traps and lures the gnats into them. I'm not sure if it's king oyster, or another oyster species/strain, but I remember it being some kind of predatory oyster fungus.

That's one way to go at them.


I saw a giant decrease in amount of gnats when I started watering from the bottom instead of the top. There's a few reasons for this: the bottom has spiders and other dwelling insects, and it's hard to reach a hole for a flying insect, it's also a fact that the top-layer (most favored by gnats) stays dry if you bottom-water. Making it useless to lay eggs in. This bottom-watering reduces the 'egg laying area' from 400cm² to around 15cm² in a single pot.


Gnats are nasty buggers, I've been dealing with them for a few years every now and then. They only show up when I really over-water substrates. I tested it, and I had to nearly drown my plants for them to show up in my house. So prevention is a good start; never let the soil go wet, unless you're growing in a bog. With most plants, that's not the case.

I deal with them by drying out the soil completely. Most plants survive a day in the shade with dried soil. Then I rehydrate the soil using dishwashing soap (to break surface tension) and emulsified (by the soap) neem oil. The plants revive pretty fast, within hours. I wait another day before putting them back in the sun.


Diamotaceous earth only works in dry form and it's only for insects that have tracheoles. Most gnats don't have that until they're adults if I remember correctly.


If you're really wanting to catch them and throw them out, being super-duper over the top organic.. There's always fruit pulp; gnats love it more than chewing on roots and fungi, place your pots on top of some fruit pulp, and they'll migrate there. Just scoop the pulp before it starts catching yeasts and starts fermenting. However, this method attracts even more gnats in the long run. That's the thing with going organic: if you don't accept pests as part of the deal, there's really no way to get rid of them without attracting more. Or you'll have to take preventive measures.


Going dry is the best way for me. The little gnat worms just crumble up in a day.


Sterilizing soil is just outrageous; you kill absolutely everything that's in there, everything that could protect your plant from seedling to adult. You'll have to add at least 3000 types of bacteria and over 40 types of fungi yourself after sterilizing. I remember a story about the Germans after world war II trying to replant a forest in sterile soil. Maybe around 40 out of the 150.000 planted trees did manage to stay alive long enough for the people to find out sterile was not the way to go with plants.


I hope this helps anyone in the future!

Good luck.

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#9 Il19z8rn4li1


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Posted 10 May 2016 - 04:50 PM

Need oil...weekly'll never have a problem again...
(Anyone that says need doesn't work, add some garlic to it and it will work even better, aside from that..there is no reason need won't work, bugs don't become immune to bad tastes and a hurt reproductive system)

Or get some Forrest duff from a nearby by wooded area, the additional fauna will add predators to keep the pest bugs in check.

Edit.. read thru thread more thorough, and lol... baked soils... come on now. Kill all your workers.

35lb bag of neem?

Need does come in neen meal form, but it's the oil you want, or Karajan oil...Pretty much the same thing.

I never believe people when they say need doesn't work, I only then assume they didn't apply it correctly and for a long enough period.

Once a week need most be used and it's a preventative, not really for infestations.
When applying, should be sprayed on leaves till plant resembles a thirsty wilted plant, then be sure to spray the entire soil surface.

If your soil is overly wet, you'll have gnat issues, mulch the soil so that you can benefit from that dry barrier.

Edited by Il19z8rn4li1, 10 May 2016 - 04:56 PM.

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