Pyrethrins against fungus gnats?

Comptine

Comptine

I think nearly all my plants have been victims to overwatering this year, this has lead to a massive fungus gnat invasion. I keep finding lots of larva in my seedlings, both chili and others that I keep indoors in our conservatory. They have also started attacking my radishes that are in a raised bed outside. 
 
I've been reading up on this, some recommend sticking a match into the soil and supposedly the sulphur is bad for the larva. Swedish matches don't really contain sulphur anymore, but I found some Russian matches at home, they might do. Not sure if this is bad for the plants so I'm currently testing this out on my disposable basil instead.
 
Anyway, pyrethrins seems to be recommended for a lot of other pests, like aphids, thrips, mites and a few others, particularly if you water it in it's supposed to hurt their larvae. I see no conclusive advice regarding gnat larvae though, so I figured I'd ask you guys if you have any experience using it for that purpose. 
 
I should add that I have added sand but two weeks later they are still around.
 
I had the same exact problem.  This is my first year growing peppers and I was very guilty of overwatering.  For the adult gnats I bought ladybugs on Amazon :)  Didn't know if it would work, but for 5 bucks and 2 shipping I thought it would at least be fun to release 300 ladybugs onto the gnats.  I'd say the results were mixed, but what really helped I think was letting them dry out.
 
I also got some beneficial nematodes (again on Amazon) which supposedly when you spray on the soil it will kill the gnat larvae.
 
Good luck
M
 
Hybrid Mode 01 said:
     Not sure about pyrethrin, but mosquito dunks (or some other preparation of Bt toxin) are pretty effective on fungus gnats. 
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Can you use the mosquito dunks on plants with pods on them? 
 
tctenten said:
 
Can you use the mosquito dunks on plants with pods on them? 
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     Oh, yeah. No problem at all. It's a really species specific poison. It only hurts the larval stage of a few types of critters like moths, mosquitos and certain flies. You could probably eat several whole ones with no ill effects. :drooling:  (Don't do that though. Just in case.)
 
tctenten said:
 
Can you use the mosquito dunks on plants with pods on them? 
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I think the dunks are bacteria based instead of chemical based. I like to add crushed dunk bits to my teas :)
 
 
Quote from Google Search:

  1. "The active ingredient in Mosquito Dunks® is Bacillus thuringi- ensissubspecies israelensis. (B.t.i.). B.t.i. is a bacterium that is deadly to mosquito larvae but harmless to other living things."
 
Hybrid Mode 01 said:
 
     Oh, yeah. No problem at all. It's a really species specific poison. It only hurts the larval stage of a few types of critters like moths, mosquitos and certain flies. You could probably eat several whole ones with no ill effects. :drooling:  (Don't do that though. Just in case.)
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Correction my friend, it is NOT a poison, it is a bacterium that is harmless. ;)
 
Proud Marine Dad said:
Correction my friend, it is NOT a poison, it is a bacterium that is harmless. ;)
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     Correction, Bacillus thuringiensis produces proteins called delta endotoxins which are lethal (far from harmless lol) to certain invertebrates like fungus gnats. It's not the bacteria that kill the pests, it's the toxins (or poisons) that they produce that do the killing. Bt toxin is a poison.
 
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