Fungus Gnats

scsva(7/VA)June 20, 2011

Need a solution to fungus gnats for my plants at the office-presently using alcohol in water to mist several times a day. In a previous post, someone mentioned soap, what is the ratio to water in the mister?

Thanks for any and all advice.


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Susan, the only way to keep plants free of gnats is by allowing soil to dry between waterings, and the room should have fresh, circulating air.

Gnats are attracted to wet soil especially when air is dry.

Thankfully, my plants are gnat-free, so I haven't any idea how to rid them, but some people vow Rubbing Alcohol, Peroxide, or soap, and other home-made recepies work.

Hopefully, someone will chime who has experienced gnats.

But, in the future, open windows, and/or run a rotating fan, and allow soil to dry before giving a drink. Toni

    Bookmark   June 20, 2011 at 1:32PM
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I had them in the past. Fungus gnats live in soil with compost in it, such as leaf litter and decomposing peat moss. As mentioned, letting the soil dry will help, but that isn't alway practical when you have plants that need to stay moist. Insecticides in the soil will work as well. For me, my fungus gnat problems stopped when I kicked peat based bagged soils to the curb, and started using 5-1-1 and gritty mixes. These mixes don't have the decomposing matter that the gnats thrive in. I think that someone did post recently saying that they had some in their 5-1-1 mix, outside though. Personally, I've not seen them since switching to it, so I feel confident recommending it to you.


    Bookmark   June 20, 2011 at 5:18PM
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Joe, I use Peat in plants that require acidic soil, and never dwelt with Fungus Gnats. I also use bagged soils, though amended with other mediums. Still, no gnats.

The problem is keeping soil constantly wet, especially in too dry or too humid conditions.

IMO there are very few plants that thrive in constantly moist soil. Other than bog plants like Papyrus.

Susan, open windows, run a fan, allow soil to dry, and you should rid those suckers..Toni

    Bookmark   June 21, 2011 at 1:58PM
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jakalfoshakal(8-9 NM)

hi everybody voyeuring over from the hoya board:) I put a mosquito dunk in my watering cans for this reason. I forget where it was that i learned this trick but have been using it for years. It works better when the dunk has been soaking for a while but i eradicated this problem last year doing this. The only "problem" per se is that you have to remember to keep a dunk in your watering cans. I believe it works by killing the larvae before they hatch.

    Bookmark   June 21, 2011 at 5:19PM
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paul_(z5 MI)

Close. The dunks contain a bacteria that proliferate in the larva's gut. As a result the larvae are unable to eat and starve to death.

    Bookmark   June 21, 2011 at 8:59PM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

I've had them many times over the years when I used to keep a huge bale of peat outside to add to potting soil. If it rains a lot, the gnats will perpetuate in those potted plants. Gnats are a sign of wet soil and are usually introduced via soil, or by placing potted plants outside in an environment that has them, like setting them in a mulched bed. They can't survive without high levels of moisture and they don't fly to distant locations to locate more.

As said, let the soil dry and only water a sip if the plants get wilty. After a few weeks, try giving a more thorough watering and see if they are gone. If not, repeat sahara treatment. A bottom-watering scheme that doesn't allow for enough water that the top later gets wet can help also but that wouldn't be practical or attractive enough for an office.

You can stick a toothpick or paper clip in the soil with tape - sticky side out - to trap the flyers near the surface. Supposedly they like yellow but I just used the tape on paperclips and got a bunch of the adults that way.

Since I've gone to a no-peat zone, I haven't seen any more appear, even when bringing outside pots in for the winter.

I would stop misting also until they are gone. That's just keeping the top later of soil moist, which is enabling the larva. If you get soap in the soil of a potted plant, it can take forever to wash out. Dish soap can have a lot of salt, too, so I don't know if that's a good idea for potted office plants that never get a cleansing rain.

I've not found it necessary to try mosquito dunks but have heard them recommended many times for this problem. Once the gnats are gone, they won't return unless you bring a new plant to the office that has them, there are other plants in the office that go untreated, or you repot with soil that has them. So perpetual watering with the dunks should be unnecessary once they are gone.

    Bookmark   June 22, 2011 at 4:01PM
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Actually I'm only seeing one or two every now and then. I do believe in misting and I add a capful of rubbing alcohol to my mister. Then I have a fan going for the humidity while I'm in the office and so far, so good.

My office has large windows and I wanted to use the opportunity to get more plants. "But" I didn't want anyone maybe complaining because of buggies flying around. I did see a few ants but decided to use the self rising flour and sugar in a bowl and haven't seen any ants in the last week.

So far, so good. Knock on Wood! LOL!


    Bookmark   June 22, 2011 at 4:09PM
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