Ugh! Gnats/fruit flies/fingus gnats all over my plants and soil.

nephifofum(8a)October 9, 2012

For weeks, I have battling these small, flying bugs that I tend to think of as gnats or fruit flies. They are so quick and so tiny that it's almost impossible to hit them with a swatter.

Somewhere, I read that the mother lays her eggs in the wet topsoil. Today, I looked at the arugula I'm growing indoors and there had to be at least 50 of the things crawling around on the top of the dirt. They could not fly, so they must have been a new batch of "babies."

I have some insecticidal soap, but it says to wait 5 to 7 days between applications. I sprayed this morning and it didn't seem to kill any of them.

Isn't there something I could put in the water I use to water the plants that will soak right into the soil and kill them without harming my plants?

I would be forever grateful if someone could help me solve this problem!


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Dave...sounds like fungus gnats.

What type of soil are your plants potted in?

Soil gnats enjoy continuously wet soil, dry/humid, stale, non-moving air.

You can either pot your plants in well-draining soil or make sure soil dries between waterings.

If it's warm outside, crack open a window and run a ceiling or rotating fan.
Before watering, stick a thin stick deep in soil as far as it will go. If the stick comes out wet, withhold watering. When the stick comes out clean, 'an example..baking a cake and inserting a tooth-pick,' clean. lol

If your soil is too heavy, it's better to repot plants in a well-draining mix.


    Bookmark   October 9, 2012 at 5:45PM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

Dave, sorry you didn't like the info I gave you already, which was very similar. But glad you're here to chat! Hope you find something that works for you and your lettuce.

    Bookmark   October 9, 2012 at 5:58PM
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I was plaged with those flies last year and I couldnt get rid of them. No matter how much I left the surface of the soil dry out.I repotted this past spring adding a lot of perlite. This fall so far I dont see any.

    Bookmark   October 9, 2012 at 6:58PM
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rhizo_1 (North AL) zone 7

Certainly fungus gnats. Yes, there is something perfectly safe that you can use when you water your plants. It's called Bacillus thuringiensis Israelensis (Bt-I). It is available as a product called Gnatrol or you can buy a pack of mosquito dunks....the things people put in their ponds to kill mosquito larvae.

Bt-I will kill the little gnat maggots in the potting mix.....which means no more adults emerging after a few weeks.

But the bigger problem IS the quality of your potting medium, watering practices, and other growing conditions. It's possible
to grow plants, even those in moist seedling flats, without seeing the first fungus gnat. I've done it for years, without Gnatrol.

    Bookmark   October 9, 2012 at 6:58PM
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purpleinopp, I appreciated your advice very much. I'm just trying two forums to make the most informed decision I can. :-)

    Bookmark   October 9, 2012 at 7:25PM
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tifflj(6 Pitts, PA)

I have heard a few things. (1) 1 part rubbing alcohol and 1 pat water in a spray bottle. The alcohol is supposed to kill the bugs but also will evaporate without harming the soil. (2) A lady told me one time to use yellow sticky paper. Which I later found out was a rat trap. I didnt have the bugs crawling in the soil as you do but I had gnats flying around the whole house. I have tried the alcohol and it didnt work for me...but I did change my potting mix and repotted all my plants and they are pretty much gone with one popping up here or there. Its been 2 weeks almost now.

    Bookmark   October 9, 2012 at 9:24PM
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tapla (mid-MI z5b-6a)

I'll toss my hat in the ring with everyone else who said or suggested an ounce of prevention ...... The best way to find relief is by examining your soil choice and watering habits, then modifying either/both in such a manner that extended periods of soggy soils become a condition associated with the increasingly distant past. I can use the superlative 'best' because in addition to being rid of the gnat issue, which is more an annoyance than a real problem, you get the added benefit of your modifications carrying with them greater potential for a healthier root system, which means greater potential for a healthier plant.

An interesting aside - several weeks ago we had a large number of fungus gnats, drain flies, fruit flies invade our home. At the time, ALL my plants were still outdoors, and I never have a gnat problem anyway; but for some reason, there were dozens of the little buggers in mainly the kitchen and a few in a lower level recreation room. They stayed about 2 days & then simply disappeared - strangest thing.


    Bookmark   October 10, 2012 at 4:35AM
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Tiff, lol, rat traps..Sticky paper rat traps.

Actually, small/yellow sticky traps, work great, trap flying bugs such as whitefly. Been there, done that.

However, I don't know if traps work for gnats..guess if gnats are flying, and trap is attached to the plant, or for those crawling on soil, gnats will end up glued to traps.

Al, is it possible the little flying insects were fruitflys and not gnats? All it takes is a small piece of ripe fruit...
You mention your grandkids visiting? Maybe one of the kiddies dropped a piece of fruit behind the couch or chair, which attracted fruitflys?? Just a thought.

    Bookmark   October 10, 2012 at 12:15PM
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tapla (mid-MI z5b-6a)

Entirely possible - I mentioned them as one of a trilogy of possible offenders in my post previous, along with drain flies. No kids - no rhyme - no reason - just came & went ...... That it was an idiopathic incident is the only thing that made it notable.


    Bookmark   October 10, 2012 at 3:39PM
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rhizo_1 (North AL) zone 7

Dave, are you still around? I'd like for you to describe the 'things' you observed crawling around on the surface of the potting soil. Fungus gnat larvae are tiny, whitish-translucent maggots that we usually only see when we water our plants. Once they pupate, their wings are fully operational.

    Bookmark   October 10, 2012 at 3:48PM
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