[ganjygav]

Hi people,
I've got a fungus gnat problem, had them before but they have never damaged plants before but the tops of my plants are yellowing with no other visible signs of any other problems.
I have noticed a lot more gnats this past week though flying around.

So I need to kill the larvae in the soil. I work a lot and find it difficult to get to the grow shops before closing. So today sent my girlfriend to get some gnat off and ask for anything else to get rid of the larvae in my soil.
I've come home and the shop sent her back with a powder called snake killer, it's bacillus thuringiensis and a liquid called fungi killer.

Both sprays for folia application which from what I read shouldn't be used within 3 days of each other.

What I really need to know is will any of this stuff kill fungus gnat larvae in the soil? I'm not lazy or stupid I have looked on Google but nowhere can I find anything about these products being used for killing larvae in the soil.

I know I've prattled on so thanks if you made it to the end haha

[RB56]

Foliar won't do it for larvae, need to treat the soil. I'd use Gnatrol. 4 drenches, 3 days apart.

[justanotherbozo]

...unless you have a large op, say bigger than 10x10, then all you need is sticky traps which don't affect the larvae in the soil except that it's the flyers who lay the eggs that become larvae.

...even in a 10x10 space a half dozen yellow sticky traps and your gnat problem will be solved within 2 weeks.

...totally organic and put and forget easy.

peace, bozo

[ganjygav]

Originally Posted by RB56

Foliar won't do it for larvae, need to treat the soil. I'd use Gnatrol. 4 drenches, 3 days apart.

Not available in the uk, it's annoying a lot of products are being taken off the shelf here in the UK for stupid reasons. Miteywash was banned because it killed a certain house spider, gnatoff was recently banned. I didn't even know and as far as I understand both these products contain nothing toxic.

Thanks for confirming it wouldn't work for soil larvae. I didn't think it would and I'm annoyed with the grow shop. They must have known it would be no good.

[ganjygav]

Originally Posted by justanotherbozo

...unless you have a large op, say bigger than 10x10, then all you need is sticky traps which don't affect the larvae in the soil except that it's the flyers who lay the eggs that become larvae.

...even in a 10x10 space a half dozen yellow sticky traps and your gnat problem will be solved within 2 weeks.

...totally organic and put and forget easy.

peace, bozo

Tiny 1.5mx1.5m with 6 plants. I've put the traps up last night so that's good. I panic though and wanted to kill the crap out of the larvae asap seeing as they are affecting two of my plants health wise.
I'm 17 days into flower that was my concern with speed.

[RB56]

I've never had luck eradicating an infestation as sticky traps. I use them - as monitors. You have to break the soil/air cycle. I did this in soil and now do it in coir:
https://www.icmag.com/ic/showthread.php?t=290400

Doing that keeps the adults from laying eggs in the medium and larvae from escaping the medium. If you do something like that to break the cycle, you may be able to get them with sticky traps since no new fliers will emerge. no new eggs will be laid.

Gnatrol is Bacillus thuringiensis subsp. israelensis, so if you can figure out a way to make a soil drench from the product you have containing Bacillus thuringiensis, you may be set.

[ganjygav]

Originally Posted by RB56

I've never had luck eradicating an infestation as sticky traps. I use them - as monitors. You have to break the soil/air cycle. I did this in soil and now do it in coir:
https://www.icmag.com/ic/showthread.php?t=290400

Doing that keeps the adults from laying eggs in the medium and larvae from escaping the medium. If you do something like that to break the cycle, you may be able to get them with sticky traps since no new fliers will emerge. no new eggs will be laid.

Gnatrol is Bacillus thuringiensis subsp. israelensis, so if you can figure out a way to make a soil drench from the product you have containing Bacillus thuringiensis, you may be set.

Maybe I could spray enough to saturate the top 2 inches of soil?

[justanotherbozo]

...yeah, i grow in 4x4 tents and have done so for nearly 10 years and EVERY time i've had a gnat infestation, and i grow in coco so that means MANY times over the years, i have solved my problem with sticky traps ONLY!

...sticky traps don't work over night but they do work, gnat flyers are attracted to the color yellow so they do land on the traps and get stuck and every one that gets stuck is one more egg layer you don't need to worry about.

...you want to speed the process up? ...add more traps.

...if you grow in a greenhouse or a warehouse then traps would be inadequate but for a small op like mine and yours yellow sticky traps and a little patience is all you need.

...another side benefit is that yellow sticky traps is TOTALLY non-toxic to your plants.

peace, bozo

PS: if the gnats don't appear to be attracted to the traps then they probably aren't gnats but might instead be white flies which, i believe, are attracted to blue sticky traps.

[RB56]

Originally Posted by ganjygav

Maybe I could spray enough to saturate the top 2 inches of soil?

I don't know. The bacteria only work against the larvae. The larvae only live in the medium. It doesn't make sense to me to have the bacteria in a foliar treatment but I did check Snake Killer and that's what they recommend. All of these bacterial treatments require living bacteria.

Amazon UK sells Gnatrol WDG.

[ganjygav]

I've been reading....
There's 2 strains of bacillus thuringiensis that gardeners in general use.
There is one for coating the roots and killing larvae in the soil that eat them - israelensis (the one I need)

The other strain is used to coat leaves to kill leaf eaters - Kurstaki (what the shop sold my girlfriend)

So what I have is no good for my needs, I'm really annoyed at the grow shop owner. My girlfriend had it in text that I needed treatment for fungus gnat larvae and at the end of the day who owns a grow shop and don't know what's used for what?

I've just got another 10 yellow traps and I will stick them up tonight as well as sprinkling some DE dust on top of soil. I spoke to another grow shop on the phone and he said he would get something in stock by monday.
I'm gonna go give the other grow shop an education on their products tomorrow and ask for a refund.