F*cking fungus gnats

b3rnd

b3rnd

I think you guys can guess what this topic is about just by reading the title... 
 
For the second year in a row these little bastards have come to terrorize my grow room. What do you guys do to kill these things? Nothing I do has any effect.
 
I'd repot everything and discard all old soil, but my seedlings are a bit on the small side. What else can I do? I have a feeling they are stunting the growth of some of my plants.
 
You guys have any great tips on getting rid of them and preventing them?
 
Beyond nuking the room and starting from absolute scratch, I got nuthin'. I'm actually thinking of switching from growing peppers to aphid ranching. I keep telling myself that I can keep my plants alive until it's warm enough to take them outside to rinse and replant, but that day is over two months off for me...
 
Luck to you, man. Hopefully someone has better "advice"...
 
May they burn in hell!

I've used an apple cider vinegar trap (jar with lid with holes poked in it) which kills a good number of them.

What I find worked best, at least in a grow tent, was to have a fan blowing on the plants for a day or 2. Depends totally on the size of your grow of course, but if you can have an oscillating fan moving over the plants, it will annoy them so much that they seem to stop laying more eggs.

I found out by accident as one of my timers for the fan was mistakenly set to on over the weekend; got rid of the damn basterds though...

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the above methods are good for controlling the infestation.
 
To actually end it you should use Bacillus thuringiensis israelensis (Bti) brand name mosquito bits / dunks.
 
Bti is bacteria which is food for fungus gnat larvae (and other Dipterans), it has a poisonous effect on them that kills the larvae after they eat it.
this ensures they do not grow up to breed, stopping the cycle of reproduction, eventually ending the infestation.
 
It is not instant, the larvae have to eat it and it gradually kills them. Adult gnats are not effected.
So as it is working there is nothing really to do or see, so some people don't appreciate it
but it is really the most effective way to end the infestation.
 
the life cycle of a fungus gnat is 3-4 weeks. so no matter which method you use, you need to be patient and keep doing your control methods for at least that long.
even if you kill every adult, there are more larvae chillin in your soil feeding on your plants roots and eggs waiting to hatch.
 
a nice thing is Bti has no effect on other organisms / plants. so you can apply it into your water or mix a bit into your soil as a preventative even if you know you're setup is prone to getting fungus gnats.
 
I feel the same way about those bastards - and they're really bad in the PNW.  I've used every method mentioned and more, sticky traps, ferment traps, white sand, fans (fans will also cause them to relocate to the walls and around the fan where many present themselves for easy smashing or just dehydrate and die), H2O2, and Bti. I have a small presence now, but I haven't really done much to combat it except proper watering and air movement from the fan.    BTW, H2O2 is probably about useless, as I've transferred larva into a 1.5% H2O2 solution and watched them wiggle for days.
 
If you really want to get rid of them, you can lessen their number with proper watering and air circulation (which I figure you're doing anyway) and traps help limit the number of adults that lay more eggs and the annoyance factor.  Then I'd use Bti as Juanitos suggests.  With Bti you need to follow the instructions carefully for efficacy (water dechlorination and allowing for the 8+ hour incubation period, in particular) and I think getting good fresh product is critical - read this as: CD got screwed over with useless old Bti before. 
 
Given the life cycle, as noted, above, it takes about 3 weeks to see any appreciable decrease in the population.  After the Bti, beneficial nematodes can be added to create a "permanent" natural control in the soil.  I've never gone as far as adding the nematodes, but I think they are needed to get a "permanent" cure in place.  Unfortunately, they're not cheap and the applications I've seen don't lend themselves to easily/inexpensively using them with lots of small containers.
 
Good luck.  They really suck.
 
D3monic said:
Before planting I fill a 5gal bucket with soil, pour boiling water in it and put a lid on for a few hours and pasteurize the soil. I dont fuck around with those bastards anymore. Kills their eggs. Didnt have a single one last year.
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Sounds like a great way to recycle used medium. I have over 100 gals of the stuff I'd rather not throw out. All bagged up and FULL of aphid nests, I'm sure...
 
Im sure it kills them, probably most the beneficial microbes as well. I usually mix a little that mito... whatcha ma spell it in after its cooled down.

Do something similar to pasteurize growing media for mushrooms
 
D3monic said:
Before planting I fill a 5gal bucket with soil, pour boiling water in it and put a lid on for a few hours and pasteurize the soil. I dont fuck around with those bastards anymore. Kills their eggs. Didnt have a single one last year.
Click to expand...
 
Well, sure, if you're going to be all logical and prevent the problem instead of struggling to fix it later.  But where's the fun in that?  :)
 
I've used the microwave before for this purpose, but it's kind of a pain to do in smaller batches.  Baking in the oven to 200F allows for bigger batches, but it's a PITA in its own way.  I'd expect boiling water treatment to make kind of a mess or create issues, at least with certain types of media. Do you mind sharing a little more about your process and the type of media you pasteurize?
 
I had my share of the little F@ckers!!! I honestly believe I brought them on by over watering. I neemed the snot out of them and caused major stress to my ow's... i put a layer of perlite, finally I threw away my first seed tray and am back in business for now lol.

This is an edit.

I did everything with advice from the good people here! Great forum, Good Luck...

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CaneDog said:
 
Well, sure, if you're going to be all logical and prevent the problem instead of struggling to fix it later.  But where's the fun in that?  :)
 
I've used the microwave before for this purpose, but it's kind of a pain to do in smaller batches.  Baking in the oven to 200F allows for bigger batches, but it's a PITA in its own way.  I'd expect boiling water treatment to make kind of a mess or create issues, at least with certain types of media. Do you mind sharing a little more about your process and the type of media you pasteurize?
Click to expand...
No mess at all, just some ocean forest potting soil, maybe a little perlite, fill 5gal bucket 2/3 full, boil a decent size pot of water, pour over the soil in the bucket thoroughly saturating but not turning it into soup. Place lid on bucket and let the heat run its course for a few hours till its cool enough to fill your seedling pots, I use 3x3x5 or maybe 7 tall pots fit 18 per tray but taller than the standard ones.

Work fine for hydrating and pasturizing coco coir as well, thats what I do for mushroom media. Coco coir and vermiculite
 
Arrghh dude that sucks I struggled with those for a couple of years, as others said sticky strips sort-of worked but was never definite.  A mix of 1:4 of 3% hydrogen peroxide to water worked much better, but a few months later they came back somehow.
 
I was fighting them like that for a while but when they came back the 5th or 6th time I was like nah screw it, switched to DWC for all my large indoor grows (apart from cross growing out etc where I have the numbers) and never looked back. Also now I can go away for a few days for work etc and not have to ask my wife to look after the plants which is an added bonus.
 
Whatever you do I hope you get rid of them, they drove me nuts.
 
I'm not sure if these pests are attracted to lights or not, but I caught several dozen of them on a yellow sticky trap on a single night where a sensor light had been triggering repeatedly which basically ended the infestation so leaving a light source and a trap near the pots might be more effective then just a trap on its own.
 
Takanotsume said:
I'm not sure if these pests are attracted to lights or not, but I caught several dozen of them on a yellow sticky trap on a single night where a sensor light had been triggering repeatedly which basically ended the infestation so leaving a light source and a trap near the pots might be more effective then just a trap on its own.
Click to expand...
Yes bright light and attracted to yellow just like white flies... uhhhg! Hate em both! Cheers

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