Need to apply Bt for fungus gnats but plants don't need water!

Rick7072(6b)November 25, 2012

I have a fungus gnat problem with my indoor herb plants and would like to apply Bacillus thuringiensis. So yesterday I bought six Mosquito Dunks and last night I cut off about 1/3 of one and put it into my 2-gallon watering to soak overnight as I've read that's good practice.

Yet my plants don't really need watering right now, and I know that over-watering provides a perfect environment for fungus gnats!

So...should I water anyway, with the understanding that this particular watering with Bt-soaked water will be helpful against the gnats? Or should I wait until the plants really need water? I'm hesitant to wait because I've been seeing the gnats for two weeks already (it took a while for what was happening to sink in!) and I know infestations can get really bad quickly.

Any advice would be appreciated.

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flora_uk(SW UK 8/9)

I would not water with the BT. Fungus gnats are symptomatic of too much moisture. Allowing the medium to dry out, disturbing the surface (just stir it a bit with a table fork, and adding a little fresh medium to the surface will fix them. There's really no need for BT at all if the watering is sorted out.

    Bookmark   November 26, 2012 at 4:46AM
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rhizo_1 (North AL) zone 7

Bt should only be applied when your plants needs to be watered. A highly porous potting mix is much more forgiving than the typical potting soil.

Flora 's advice is good, though I'd incorporate perlite rather than more potting soil.

    Bookmark   November 26, 2012 at 8:41AM
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I got fungus gnats one year from a bag of organic potting soil. No matter how carefully I watered, it did not help get rid of the gnats! I used the Bt dunks when I watered, still had them. I read to sprinkle cinnamon liberally on the soil surface. It took a week or so, but that did the trick.

    Bookmark   December 22, 2012 at 12:19PM
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I've heard about using cinnamon and will try it. Is it well-known as an insecticide? Is it targeted specifically to fungus gnats or is it a general insecticide? How does it work? I think I'll do a little internet research. Thanks.

    Bookmark   December 22, 2012 at 7:02PM
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Cinnamon doesn't work either. Put a glass of vinegar near your plants and the fungus gnats will disappear. If the vinegar evaporates, rinse the glass out and refill it.

    Bookmark   January 10, 2013 at 2:06PM
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gjcore(zone 5 Aurora Co)

I find that neem oil spray works pretty good for fungus gnats. Might take a couple times through to get rid of them.

    Bookmark   January 10, 2013 at 9:31PM
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Thanks, since I posted that message I've been using neem oil and it does seem to be working pretty well.

    Bookmark   January 10, 2013 at 9:49PM
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