war on fungus gnats!! (and all natural too!) =)

jungleboogieJune 14, 2007

Alright everyone, I know you know what I'm talking about... the dreadedly annoying fungus gnats (or 'dirt flies' as I used to call them before I figured out what they were). Like most people, when a few of them showed up, I underestimated them considerably and thought nothing of it. Now, they're everywhere and I can't seem to get rid of them. I've used the yellow fly traps, as well as a white powdery thing called "Wilson's Fungus Gnat Killer", which worked for awhile, but I have no idea what it's made of and, frankly, I'm afraid to use it again because of the warnings on the labels. I dehydrated the heck out of them over several months with only minimal "emergency measures" watering, and they still came back.

Anyway, they're back in full force and seem to keep finding new and creative ways to die around the house (some of them are even smooshed against the glass on the inside of a picture frame!?!) =S I've scanned the web and people have had a number of good ideas, with mixed success. So, I'm planning on combining them all into one major all out, winner-take-all cage match assault on them. I'm going to do this without any chemicals that will kill the neighbours pets or make me grow a third arm.

Here is my plan:

1) I will put a layer of sand on the top of the larger pots since the FGs like the top few inches of soil.

2) I will water sparingly

3) The water I use will be infused with peppermint tea (1 bag per litre)

4) The water will be hot (not scalding, but warm enough to kill the larvae and cool enough to not bother the plants)

5) yellow sticky flags to catch the adults

6) a few bowls of sugary water here and there to do the same. For some reason they just love to drown themselves in water. It's amazing they live long enough to reproduce at all.

Anyay, that's my all out, all-natural assault on these really annoying pests. Hopefully, they've swan dived into their last bowl of cereal in this house! =)

Any thoughts or suggestions are welcome. I will keep you posted about what works and what doesn't. Operation Gnat commences in t-minus three days, when I water them next.


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Do you know the potato trick? Haven't tried it personally, but I believe it -- the story is that the larvae will be attracted to pieces of raw potato left on the surface of the soil. Leave it there long enough for them to get to it, and then pull it up and throw it away: they'll stick to it and you can get rid of a bunch of them all at once, before they ever get to be adults.

If you're serious about eradicating them completely, you should know that the life cycle is about four weeks long, so you might be doing all this for a while.

Here is a link that might be useful: About fungus gnats

    Bookmark   June 14, 2007 at 11:47PM
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watergal(z6/7 Westminster, MD)

Also pour some bleach down all your drains. Sometimes they set up housekeeping in their too.

If you have standing water around anywhere (humidity trays or whatever), get rid of it. Check all the bottoms of your pots and saucers to see if there's any standing water hiding in there.

Be sure to lay the sticky traps horizontally, not vertically like they are used for other pests.

Peppermint tea, huh? Hadn't heard of that one before.

I recently attended a lecture by an expert on using beneficial insects, and she was bemoaning how fungus gnats are becoming resistant to Bt, a natural bacteria used to kill them. Gnats are becoming more and more prevalent in the soil of plants our company buys from Florida, even from the good wholesalers. It is a serious problem. I would quarantine any new plants you buy, and try to buy potting soil that appears to have been stored dry, not out in the rain.

    Bookmark   June 15, 2007 at 12:25AM
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mkiker(Marshall zone 8 NC)

I think better than fly paper or sugar would be the little bee catcher bottles. Google it if you don't know what I mean.

Skip the hot water. If it's hot enough to kill larvae in the soil it would probably scorch the plant.

If you have water in humidity trays then add salt to it. It kills larvae of mosquitoes so I assume it would do for other stuff also.

    Bookmark   June 15, 2007 at 1:33AM
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Wow, you guys have great ideas..never heard of most of these tricks, but they sound ideal.
Jungle, sounds good to me..I'm thinking you're talking about sticky traps instead of fly paper right? Those w/glue on both sides???
Great ideas..if I ever get fg's I'll have to remember these tidbits..Toni

    Bookmark   June 15, 2007 at 1:15PM
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Yeah, thanks for the extra ideas everyone. Very helpful. It's a united front! =)

hopeful: Yeah, definitely the sticky traps. there are several types out there, the kind I got are little green plastic sticks that you put in the soil and two spots to put these yellow strips of sticky paper that stick out horizontally. It's definitely not fly paper, but I bet that would work too... these things are always looking for a new way to die. Again, I'm stunned the species survives at all since they actually seem to want to die... but I guess since "each female lays 100-300 eggs in batches of 2-30 each" (thanks for the link and info Mr Subjunctive), it's just the ridiculous number of them.

Anyway, I have no idea if any of the above methods work, but I'm going for the shotgun approach. If each method works even a little bit, then having them all going at the same time 'should' get rid of them. *fingers crossed*

Watergal: thanks for the tip about the drains... I had a few plants in my bathroom and the gnats love it in there. I barely see any or catch any around the plants, so that has to be it. thanks!


PS T-minus 2 days until FG destruction begins. =)

    Bookmark   June 15, 2007 at 2:36PM
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mkiker(Marshall zone 8 NC)

What would happen if you put that 1/4 inch of sand and then put a thin layer of potting bark? It would look better I think. Except for cacti that is. I have some cacti and I think I'm going to put sand on their top soil. Would the potting bark be enough medium for the gnats to grow in? The bark wouldn't stay wet because the sand below it so I'd assume the gnats would die anyway.

If not you could put aquarium rocks on top of the sand. That is unless you like the way sand looks in your pots. I'm a bit OCD about it and insist on quality potting park on all of mine. Dirt just looks to cheap and all :)

    Bookmark   June 15, 2007 at 3:54PM
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The nasty little buggers are attracted to yellow so if you are going to put out bowls of water, put some yellow food color in it or use a yellow plastic bowl. I don't know if the sugar is necessary, they dive right into the plain water and drown anyway. I drench the soil with Knock-Out Gnats periodically (a BT product which is still working for me) to kill any larva.

I think no matter what, they will persist. I also have heard from many people that the leading brand of potting soil is often infested with larva and when the company was contacted they shrugged it off saying they did not claim to have a sterile product. If you bring bananas in from the grocery store or tomatos from the garden, I think you are renewing the population.

Sometimes I resort to a flying insect spray with pyrethrins and just mist it around the plants.

It's a constant battle. Bugs are the bane of my existance!


    Bookmark   June 16, 2007 at 6:12PM
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Howdy Jungle Boogie: I am currently dealing with maybe the worst infestation of FG ever. For a bug that does relatively little harm to the plant, they sure are a nuisance.

Since we are always keeping the surface dry to make it harder for them, we can spread diatomaceous earth (D.E.) onto the soil. It works until it gets wet. The bugs landing onto it or emerging into it will be dessicated. This leaves watering sparingly (from the saucer, from the bottom, from the tray) to keep the plant from dying. As someone stated, emergency watering only.

Rotenone added to the water (and/or soaking the whole pot in water laced with rotenone) might work, but I have to try it. I am off to get the supplies to test what has been given here.

Randall Prue, Montreal Plant Doctor
Author: Keeping Them Alive

Here is a link that might be useful: Montreal Plant Doctor

    Bookmark   November 2, 2010 at 7:34PM
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