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Greenhouse: HELP Fungus Gnat invasion

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Forum: GreenhouseReplies: 5, Views: 125
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Arlington, TX

January 5, 2013
3:54 PM

Post #9376452

I have a shelf with fl. lights where I keep some cactus and succulents, some all year some just for the winter. I also have some Nepanthes and sundews. I got some new sundews (5) and now I see gnats in the LFS moss in the CP pots. How the devil do you get rid of these? I don't think they will bother the other plants, too dry. But I did have to toss one orchid that was in prime agra (sp?) rocks that was full of them. I checked the other orchids and they seem fine. Suggestions? I got to get rid of these things!!!!!!!!!!!!!!!!
Priest River, ID
(Zone 5b)

January 6, 2013
10:15 PM

Post #9377756

Try gnatrol. Google it . I had a problem with the fungus gnats in my greenhouse grown peppers this summer. I used the gnatrol and also used an inch layer of sand on top of the potting soil. The sand is supposed to dry out quickly enough to prevent eggs from successfully hatching in the soil. Between the 2 prong approach, I got the situation under control. Good luck.
Arlington, TX

January 7, 2013
12:29 PM

Post #9378294

Thanks I will look it up.


Everett, WA
(Zone 8a)

January 22, 2013
5:56 PM

Post #9394139

>> gnatrol and also used an inch layer of sand on top of the potting soil. The sand is supposed to dry out quickly enough to prevent eggs from successfully hatching in the soil.

Screened bark nuggets from 3/16" to 3/8" are sure to dry out quickly. (or 4-10 mm)

And they're cheaper than screened, washed grit.
But can gnats burrow between the chunks to reach the soil?


Northeast, PA
(Zone 6b)

February 9, 2013
4:51 AM

Post #9412820

I have some fungus gnats on my sundews and carnivorous plants. I figure they are food for the plants & so far are not too much of a bother. I think trying to keep the surface dry will be difficult since they are bog plants. I would try gnatrol as well as a solution. That shouldn't bother the plants.

Osler, SK
(Zone 3b)

May 18, 2014
10:21 AM

Post #9842217

I guess this message is late for you, but in case other people are looking for it I will tell you what I do.

When I first plant a crop, I put in a mite called hypoaspis. I actually use it more because I want the thrip control, but the mites also like to eat fungus gnats.

If I get an outbreak of the gnats, I spray beneficial nematodes (Steinernema feltiae). These nematodes also help with other insects, so I really like them.

Of course, this is probably overkill if you only have a few pots with the issue, but if you have a bigger outbreak in your greenhouse you could consider these as alternatives.

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