Fungus Gnats and Pyrethrum

I have a few questions:
1) Can you kill fungus gnat larvae by drenching the soil with a pyrethrum based solution?
2) Can you kill fungus gnat larvae with hydrogen peroxide (h2o2)? Will this kill the plants? If not, what is the best strength?
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OK. I'm just telling. I googled for "fungus gnats" and found a wealth of information in just the first 9 results, minus #4, which was a site for a company that sells chemicals. The others were all university sites, and very informative.
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wrote:

I use Gnatrol, but you can get same results by buying some pond donuts which are called Bt-Israelensis. Soak the donuts in hot water and when it cools water the plants. I don't use pyrethrum based poison. You could also cut way back on watering and get rid of them that way.
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How about quick, simple, cheap, non toxic and always works.......would that suit you?
Sprinkle the surface soil with ground cinnamon. The gnats disappear within minutes and apparently it kills the eggs and larva because I've never gotten a re-infestation in the pot. I was taught this trick by a lovely old man who had two green houses full of orchids and exotic rare plants. I've used this method for years with my house plants and told numerous friends and all have had success and no harm done to any of their plants.
I bought a jar of ground cinnamon at the dollar store and tossed it in my plant stuff bag I keep in the closet. Whatever is in the spice has no bearing on price for success.
Give it a try, Val
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If the gnats are a problem on houseplants, you can smother them by covering the potting soil with one-half inch of sand.
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Just Asking wrote:

Yes. Also, permethrin family insecticides, synthetic pyrethrins fine tuned for better kill and longer persistance.

I've used 3 percent drugstore peroxide cut to 1/2 percent without causing noticeable harm. Kills the gnat larvae indirectly, by killing the fungus that turns healthy root hairs into gnat food.
Tried cultural fixes? Try root pruning and repotting in clean soil. Then cut back on water. Drowned (and dead) roots is what draws gnats. Near-terminal cases may require taking and rooting cuttings and hoping the fungus infestation hasn't become systemic.
Have you done a potato test to get a positive on fungus gnat larvae? I wonder if it would be possible to use spud slices as bait to draw the little buggers to your dose of pyrethrin or BtI, allowing more kills with less poison?
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Val and Father Haskell,
Thanks a lot, that is great advice. I expecially will try cinamon (in combination with neem oil for the adult insects). And I finally have a good dose for the H2O2 solution. I'll also try a soil drench with pyrethrum, when my plants are more established.
Thanks.
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