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Attack of the gnats....

Posted by lucilleclifton Zone 4 (My Page) on
Thu, Apr 10, 14 at 10:00

OK, I clearly have a gnat problem. I knew this, but I only realized the scope of it last night when I pulled my shelves away from the window and saw a virtual city of gnats hanging out on the window pane behind the shelves. This started b/c I used those stupid greenhouse domes when germinating my seeds (never again). Here's what I've tried to get them under control so far:

-Box fan on low blows directly on the seedlings
-I put cinnamon on top of the soil
-I watered with a 25% hydrogen peroxide solution
-I have yellow sticky traps up
-I dusted with "Safer garden dust" (which has BT).*
-I sprayed with Neem.*

* These I did not do to the very young seedlings that don't have true leaves yet: my serrano peppers, king of the north peppers, basil, parsley, and tomato.

Last night I vacuumed every gnat I could find on an around the window. Then I removed the seedlings from the trays and vacuumed those out too. Then I periodically have gone to inspect and hand-crush any gnats I find. The numbers have diminished, but I still find new gnats every time I go back.

One tray of plants is just a few days from being finished hardening off and getting transplanted outside. The other has the babies that are still growing.

What else can I do/try?

Thanks!


Follow-Up Postings:

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RE: Attack of the gnats....

Last year I had a huge infestation like you when I was growing my tomato/pepper seedlings. They traveled all over the house and were so annoying. Like you, I tried everything except the Safer dust.

This year, I found something that absolutely works! Mosquito Bits made by the people who make the mosquito dunks. I just sprinkled some on top of the soil and every time I water, some of the BT goes into the soil. No knats this year.


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RE: Attack of the gnats....

  • Posted by digdirt 6b-7a North AR (My Page) on
    Thu, Apr 10, 14 at 10:44

The Bt you need is BtK strain. The Mosquito Bits and Mosquito Dunks are the commonly recommend source for it. Lots of discussions the search will pull up.

The bits can be sprinkled on the soil but work faster when dissolved in some water and poured into the soil. The gnats have to ingest it for it to work.

With the Dunks dissolve 1/4 of the ring in 2 gallons of water and use it to lightly water the plants.

BtK is approved organic and poses no threat to the seedlings.

Dave


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RE: Attack of the gnats....

  • Posted by morz8 Z8 Wa coast (My Page) on
    Thu, Apr 10, 14 at 11:22

Lucille, the BT in Safer Garden Dust is the subspecies for caterpillars, it won't help with the gnats so save it for outdoors.

I think Dave meant to suggest BTi, or Bacillus thuringiensis subspecies israelenis - that's the one effective for gnat and mosquito larvae, the 'K' is specific to caterpillars.

It's available in several products (Gnatrol, Knock Out Gnats etc) or easiest to find at least in my smaller community, the above mentioned mosquito dunks.

Float the dunk in a container of water overnight, then use that water for your seedlings. It's a very effective but not instant fix - the larvae need to ingest it to break the breeding cycle of the very short-lived adult gnats so don't expect it to work immediately like some kind of contact insecticide might. Use the treated water each time you water on your normal schedule, and the gnats will evolve from diminished to gone in approximately 3 weeks.

Happens to all of us from time to time. I sowed some iris seed that I knew would take several weeks to germinate this winter, using a potting soil from an opened bag in my garage, put the seed pots in a zip lock bag. Two weeks later I noticed gnats but thankfully zipped in. And I do keep a small supply of Gnatrol here, dated - the dry form has a shelf life of about 2 years is what I'm told - treated the pots and eliminated the gnats before they got out of control.


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RE: Attack of the gnats....

Sounds like the delivery method is mainly watering... one concern I have is that I don't want to over-water the seedlings just to deliver poison to the gnats.

I just thoroughly watered everything yesterday. I know this is subjective based on how dry the soil feels, but how soon is too soon to water again with a mosquito dunk? If I wait a week, couldn't my gnats quadruple their numbers between now and then?


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RE: Attack of the gnats....

  • Posted by digdirt 6b-7a North AR (My Page) on
    Thu, Apr 10, 14 at 13:58

Thanks for catching the error morz! I get so used to typing BtK that my fingers do it automatically. Sorry about that Lucille. Bti is what is needed.

As to the watering with it, it takes just a very small amount - a teaspoonful or so. Or you can wait until they need watering normally and use it then but meanwhile they will multiply..

Or you can buy the bits if you can find them.

Dave


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RE: Attack of the gnats....

So the bits work on them even before they're "watered in?"

I'll check my local garden center tonight, will find one or the other! Thanks all.


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RE: Attack of the gnats....

  • Posted by digdirt 6b-7a North AR (My Page) on
    Thu, Apr 10, 14 at 15:20

The bits work as they dissolve. If the soil is moist they will slowly absorb the moisture and dissolve.


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RE: Attack of the gnats....

It won't kill the knats that are currently flying around but they only live for a few days. The BT kills the larvae. It doesn't take much water to get the bits into the soil --- I never over-water.


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RE: Attack of the gnats....

  • Posted by morz8 Z8 Wa coast (My Page) on
    Thu, Apr 10, 14 at 16:08

'over-water the seedlings just to deliver poison to the gnats'

Most of what you see with the dunks, bits, or even granulated form of BTi is 'inert ingredient' used as a carrying agent that then releases the BTi into water. It's not a poison, its a naturally occurring bacterium that is harmless to us, birds, fish, our pets, but stops the development of only mosquito and gnat larvae when they ingest it.

If you had some of the water/liquid prepared and your soil is already moist, pour in just enough to introduce some of the released bacteria to the potting medium, you don't have to drench. Then next time you water, go ahead and give the pots your usual amount of water and do that with the treated water each time until they are really gone. The adults aren't causing any damage and only live a matter of days so you don't really have to exhaust yourself chasing those. You don't want the larvae to mature to more adults so are treating the soil. Also, you seem to have a full blown case of gnats now, one overwatering if you were to do that isn't going to make it worse ;)

Dave, with as much as you grow, I thought you knew the difference in the BT and just had a case of fingers on keyboard getting ahead of you ;)


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RE: Attack of the gnats....

  • Posted by digdirt 6b-7a North AR (My Page) on
    Thu, Apr 10, 14 at 17:05

Dave, with as much as you grow, I thought you knew the difference in the BT and just had a case of fingers on keyboard getting ahead of you ;)

Its all the dirt under my fingernails this time of year!! Falls into the cracks in between the keys. *grins*

Dave


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