newbyplantlover
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getting rid of fungus gnats

Hello

I've figured out from fishing around on here that the fruit fly looking things that are flying around my plants are called fungus gnats. The problem is that I have about 25 different plants under a plastic greenhouse, and I have no idea which has the gnat problem. Of course, an issue there is also making sure the gnats don't start nesting in another plant as well ...

I have heard that soaking the plants in soapy water should kill the gnats, but I'm concerned about how I'm going to pull that off. Most of these are tropical indoor plants which can't handle the very hard water we have up here, and I'm not sure how to soak them in soapy water without damaging them in some way.

So my question is: is there a good was of identifying which plant(s) actually have the gnat problem, and also: what other methods of getting rid of these pests do I have?

Thank you!
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Kisal
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You can lay a slice or two of raw potato on the surface of the soil in each container. Wait two or three days, then turn the slices over. If there are fungus gnats present in the soil, you should see the larvae on the potato slice.

You can buy yellow sticky traps for this purpose if you prefer.

Here's a link that includes information for biological controls that might be safe for your plants:

https://www.hort.uconn.edu/ipm/greenhs/htms/biocontrol_fungusgnats.htm
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams

a0c8c
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You need to address the fungus problem, not just the fungus gnat problem. Your soil is staying too wet, you need to let it dry.
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GreenThumb07
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Gnats Problem

There our two products I have used for gnats and all other kind of sticky pests and bugs that you don't want in your garden. One is Azamax which can be sprayed or given in a normal watering cycle, this product is also organic and omri listed. There is also SM-90 which is a great product as well but is not organic, and you can only give that in water you cant spray. I suggest you get something that you water into your soil, that is going to take care of the problem better than spraying the plants. I know a great place that you can locate those products if needed. Hope you have a great weekend !!! :P

newbyplantlover
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Kisal wrote:You can lay a slice or two of raw potato on the surface of the soil in each container. Wait two or three days, then turn the slices over. If there are fungus gnats present in the soil, you should see the larvae on the potato slice.

You can buy yellow sticky traps for this purpose if you prefer.

Here's a link that includes information for biological controls that might be safe for your plants:

https://www.hort.uconn.edu/ipm/greenhs/htms/biocontrol_fungusgnats.htm
Thank you! I'll try the raw potato. I have found a couple plants that I could see larvae on the bottom roots of, but I don't know if I've got them all. Thanks for the link as well!
Plants are just so happy.

newbyplantlover
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a0c8c wrote:You need to address the fungus problem, not just the fungus gnat problem. Your soil is staying too wet, you need to let it dry.
Thanks. I thought of that, and am trying to. Many of my plants cannot afford to be dried out to the extent that I think it would take to kill these bugs. I'm working on the moisture issue.
Plants are just so happy.

newbyplantlover
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Re: Gnats Problem

GreenThumb07 wrote:There our two products I have used for gnats and all other kind of sticky pests and bugs that you don't want in your garden. One is Azamax which can be sprayed or given in a normal watering cycle, this product is also organic and omri listed. There is also SM-90 which is a great product as well but is not organic, and you can only give that in water you cant spray. I suggest you get something that you water into your soil, that is going to take care of the problem better than spraying the plants. I know a great place that you can locate those products if needed. Hope you have a great weekend !!! :P
Thanks very much! Due to the abundant water issue mentioned by the previous responder, I'm not quite sure how to make a water method work well without overwatering them. I'll puzzle on this for awhile.
Plants are just so happy.

Dillbert
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surprised no one mentioned this....

fungus gnats love the wet soil surface. they live & breed there.

so, gets some coarse sand, put about 1/2" layer on the soil.

soil surface no longer wet, gnats got an environmental issue . . . .

newbyplantlover
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Dillbert wrote:surprised no one mentioned this....

fungus gnats love the wet soil surface. they live & breed there.

so, gets some coarse sand, put about 1/2" layer on the soil.

soil surface no longer wet, gnats got an environmental issue . . . .
Thanks! I'll see what I can do about coarse sand. So they don't actually live in the dirt around the roots, then? They live on the surface?
Plants are just so happy.

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Kisal
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The larvae live and feed in the soil. They do eat living plant tissue, primarily the small feeder roots. This is a good article about them, and it has 2 links at the end to additional articles with good information. All of the article suggest insecticides ... pyrethrins ... but my choice would be to use the Bt. JMO! :)

https://extension.oregonstate.edu/news/story.php?S_No=772&storyType=garde
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Sage Hermit
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fungus nats can be killed easily its not too difficult.


Really wet soil is what I'd look for first!

then I'd look for the nats. You can see em flying around your soil. That should indicate that soil has some eggs in it.

Some people use cinimon to kill them off.

The best trick is destroy their environment and poison them. to do that I add some cinnemon , put a fan on that pot and stir the soil a little to aerate it. the fan also deters the nats greatly.

I have not tried the sand method myself but the cinnemon and sand method apply the same principle to destroy and pollute the surface environment. 8) There are probably a hundred other ways you can do away with them.
You can solve all your problems in a garden/laboratory.

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applestar
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OK -- I'm 100% sold on SUNDEWS as fungus gnat control. After seeing [url=https://www.helpfulgardener.com/forum/viewtopic.php?p=120194#120194]toil's thread[/url] I bought one of the filiform (wasn't labeled) and a couple of tiny paddle shaped ones, as well as a VFT. The sundews are TOTALLY covered with fungus gnats. :twisted:

GreenThumb07
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You are welcome, that is what we are all here for is to help each other out. You should let your plants dry out as much as possible but not to the extent that they are wilting. It is good for your soil to dry out completely but you don't want your plants wilting either. When there is no water in the soil there is nothing for the gnat to thrive on. That is why I like the SM-90 you feed it right into your regular watering, and you don't have to dry your plant out. You let the product do the work. Hope you have a great day, and good luck with your problem.

Swivel
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1\2 an inch of very very fine sand atop the soil. If they cant get in or out the sruface than how will they live and breed within the pot? I keep a bag of sand for new plants and have not had nats for a couple years now.
Everything is chemical, not everything is logical.

Toil
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applestar wrote:OK -- I'm 100% sold on SUNDEWS as fungus gnat control. After seeing [url=https://www.helpfulgardener.com/forum/viewtopic.php?p=120194#120194]toil's thread[/url] I bought one of the filiform (wasn't labeled) and a couple of tiny paddle shaped ones, as well as a VFT. The sundews are TOTALLY covered with fungus gnats. :twisted:
this year I woke my sundews early and my fungus gnats are very much in check.

and one had babies!

on another note: please don't eliminate fungus! Fungi help allow you to keep drier soil in the first place. And remember that fungus gnats in proper numbers are a good thing. They are pollinators for fungi basically, mostly good ones I assume (until proven guilty).
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