Neem Oil And Possible Gnats

letrangerJuly 27, 2008


I grow a few plants here and there inside my apartment, namely African violets, aloe and herbs.

I water my plants every few days or when the soil looks dry.

When I stare at my plants sometimes I see tiny little white bodies moving in the soil, they are like tiny little dots no bigger than 1 mm each. I see them the most when I water the plants.

Are those gnats? And I also see a tiny little black fly.

I have some neem oil at home. Can I make a solution of it with water and soap and use that to water my plants? Will that get rid of the gnats?

And how should I water to avoid them?

Thank you.

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morz8(Washington Coast Z8b)

My own experience is that once you have the gnats, nothing gets rid of them other than BTi - Bacillus thuringiensis subspecies israelensis, the same BTi used for mosquito larvae control (safe for pets, people, fish, birds). More careful watering habits may prevent getting them again, but it's hard to let the soil dry out enough (all the way to the pot bottom, I've seen the gnats go in and out of the drainage holes) to kill the larvae in the soil, stop the breeding cycle, without damaging plants. Others have suggested a layer of sand on top potting soil, cinnamon etc...I needed the BTi to rid my plants of the gnats after bringing home a herd of them in a new plant - they infested every pot in every room of my house.

There are water soluble commercial preparations made that are easy to use, Knock Out Gnats, Gnatrol etc, or - mosquito dunks may be easier for you to find and you can make your own solution by floating a mosquito dunk in a container of water overnight, then using that water to water your plants...for a minimum of three consecutive waterings on your regular schedule or as your plants need water. Then give the balance of the package of dunks to a friend with a water feature in their garden :)

    Bookmark   July 27, 2008 at 9:44PM
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If your potted plants do have these "fungus gnats" you will see a lot of the adults flying around the plant as well as the larva wiggling in the soil. The larva need a fairly moist envirnment to grow in so checking the soil carefully before watering is always necessary and keeping the plant a bit dryer than you think it can stand will help a lot. Yellow sticky traps can help trap the adult flies so they do not mate and lay more eggs that will become more larva that wil become more adults, because the only reason the adults are there is to lay eggs.
The BTi suggested above might be necessary of just letting the potting soil get dryer does not, but using Neem Oil products would be more like using a bazooka to kill a mouse.

    Bookmark   July 28, 2008 at 7:48AM
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Thank you very much for your response.

I suspect that the gnats actually come from/ with the bag of potting soil I bought-- when I opened the bag today this second time of using it i see quite a few little black flies coming up, even more than what I have around my plants.

For my potted plants, I have for now implemented a few measures, and will see if they are useful or not:

1. wait for soil to get as dry as it can be before watering
2. place a little cup of red wine next to the plants for adult gnats are attracted to the fermented smell of it
3. put some cinnamon on the soil so to fill the fungus living in the soil, leaving no food for little worms, mixed in a bit of coffee ground and dried tea leaves (just for the fun of it); if this doesn't work I'll try sand
4. a very weak solution of neem and tea just to be safe

    Bookmark   July 31, 2008 at 3:07PM
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morz8(Washington Coast Z8b)

#3 still leaves you with one food source for the gnat larvae - the main reason we become concerned over infestations of the gnats (not that swatting adults is anyones idea of entertainment :))

"The adult stage is primarily a nuisance, whereas the larval stage is directly responsible for plant injury by feeding on plant roots or tunneling into stems. In addition, larva can vector soil-borne pathogens directly through feeding or creating wounds that allow entry for soil-borne pathogens."

    Bookmark   August 1, 2008 at 12:10PM
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Yes I do think that adding organic matter might not be helpful at all in my case, I guess I was hoping the cinnamon would kill of fungus in soil.

I guess I'll have to head of to a gardening centre to get some sand then -- I was at a beach today but wasn't sure if the sand there was clean enough or not for gradening purpose lol! And also see if I can find the BTi thing.

One thing is find curious though -- I still don't see any larvae like things on the soil.

And the red wine doesn't seem to be attracting the adults either -- maybe it's too cheap a wine. lol.

    Bookmark   August 2, 2008 at 1:30AM
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rhizo_1 (North AL) zone 7

You are confused, me thinks. They are not called fungus gnats because they feed on fungus. The larvae are found in organic-y (like your potting soil) soil or potting mixes and feed on that kind of debris. When in large numbers and confined to a container, they will also feed on tender plant roots.

Fungus gnats are not like fruit flies in that the adults will never be attracted to juice, vinegar, or wine. Fruit flies can be trapped by such liquids because they lay their eggs in over-ripe fruit. Fungus gnat adults deposit their eggs in that moist, organic-y environment of the potting medium.

Best not to use beach sand for your containers. Sharp builder's sand is a good product for this purpose. But, if you have a really bad infestation, don't hesitate to locate some of those mosquito dunks. They should be readily available at this time of year.

    Bookmark   August 3, 2008 at 4:29PM
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Thanks Rhizo_1 !! I also think that i'm probably really confused too! I'm very new to gardening and being easily intimidated by bugs doesn't help much I guess!

I don't think it's a really bad infestation for now: usually I find less than 10 resting/ flying around my 10 or so pots, most of the time 5-6.

So I'll go discard the wine and maybe look for some sand if needed. Can I use those packs of sand sold at gardening centers?

    Bookmark   August 3, 2008 at 8:52PM
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morz8(Washington Coast Z8b)

Is it horticultural grade (coarse) sand? I haven't looked for small bags, the last time I bought sand (builders grit) it came in an 80# 'tube' - probably not something an apartment dweller would want. Horticultural grade sand is similar to parakeet grit...most grocery stores would have parakeet grit in small boxes in their pet supplies section.

Just remember, sand on top doesn't deter the gnats from flitting in and out of the drainage holes to lay eggs.

    Bookmark   August 4, 2008 at 12:47PM
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I don't really know what kind of sand they are as I merely walked pass them.

What is the ultimate way to eradicate gnats if even sand are not useful?

    Bookmark   August 5, 2008 at 4:43PM
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morz8(Washington Coast Z8b)

BTi - Bacillus thuringiensis subspecies israelensis

Found in liquid form Gnatrol, Knock Out Gnats, probably others, and water feature/garden supplies for mosquito larvae control, i.e. mosquito dunks etc

    Bookmark   August 5, 2008 at 9:24PM
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Sand and BTi, here I come!!

Well, maybe after I deal with the new comer-- Aphids!!

ahhhh...... I just realized that gardening is a life long battle.

    Bookmark   August 6, 2008 at 12:09AM
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Oh my-- I have been to two gardening stores and none have any BTi products nor mosquito dunk.

I guess i'll just have to live with them for quite a while! =(

    Bookmark   August 8, 2008 at 1:29AM
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rhizo_1 (North AL) zone 7

I've seen the mosquito dunks packaged on cardboard 'hangers' so that they can be displayed all over the pest control section of big box stores. I'll attach some pictures for you so that you know what they might look like. Also, they would be readily available on-line.

Here is a link that might be useful: click here

    Bookmark   August 8, 2008 at 11:16AM
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letranger, fungus gnats and fruit flies are often confused but there is one difference which tells them apart easily. The adult fungus gnats are attracted to the human face (apparently it has to do with carbon dioxide and NOT my good looks), whereas the fruit flies tend to cluster around the fruity stuff. I have read that small pieces of raw potato placed on the soil surface will attract the larvae of fungus gnats but I cannot vouch for that. I have potatoes and plants but so far, no larvae. Maybe the potato thing is not not a reliable guide.

    Bookmark   August 9, 2008 at 4:16AM
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I think I should ask this very obvious question after a few days of BTi hunting without any success... is mosquito dunks sold in Canada?????

Or, any reliable online retailers who would ship it to Toronto?

    Bookmark   August 12, 2008 at 1:59AM
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