Ask a Question forum: Annoying Fungus Gnats!

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Name: Crissy
Fallston, Maryland
CrissyJones
Feb 18, 2016 9:19 AM CST
Has anyone tried the peroxide and water regimen in houseplants to kill gnat larvae? Been looking on YouTube for remedies because they are so annoying. I took all my houseplants outside yesterday in 50° temps to get the gnats out of the dirt. Surprisingly I haven't seen any flying since, but was told there are probably eggs in the soil that will hatch when I resume watering unless I use peroxide.......Open to suggestions and tips. I don't want them to come back as I have over 40 something plants in my home.
Name: Jennifer
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jvdubb
Feb 18, 2016 9:30 AM CST
I never noticed much difference with the peroxide. I installed the yellow sticky squares and that helped. But the biggest thing was I started letting my plants dry out and that has worked the best for me.

Also Welcome! Welcome!
Name: Ken Ramsey
Starkville, MS (Zone 8a)
[url=www.tropicalplantsandmore.com]
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drdawg
Feb 18, 2016 9:40 AM CST
Welcome to ATP, Crissy. I have never used peroxide to kill/control fungus gnats but I am sure there are those that can give you advice. I use yellow, sticky cards to keep my insects at bay. Here is one of those cards and it has been sitting next to my adeniums for not quite four weeks. It is easy to see the gnats, though more than one can count, but there are probably about 1/2 as many white flies stuck on the card as well. Both sides of the card is shown.

Thumb of 2016-02-18/drdawg/82279e Thumb of 2016-02-18/drdawg/0f3f87

drdawg (Ken Ramsey) - Tropical Plants & More
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Name: Crissy
Fallston, Maryland
CrissyJones
Feb 18, 2016 9:40 AM CST
Thank you very much!....Yes I have homemade yellow sticky traps with yellow index cards and vaseline. (YouTube).. lol. Also apple cider vinegar with sugar and water in little bowls scattered about my various plant stations. I see no activity as of yet when prior to taking them outside, I could walk past a pot or tap it and had instant swarms..uggggh! I like to think the cold killed them although I know that isn't true... lol. .. Alot of them are drying out and maybe this too is the reason for no activity, I just don't want to water them again and then poof. BUG METROPOLIS again...hahahaha.

Name: Ken Ramsey
Starkville, MS (Zone 8a)
[url=www.tropicalplantsandmore.com]
Orchids Greenhouse Vegetable Grower Ferns Region: United States of America Hummingbirder
Composter Bromeliad Master Gardener: Mississippi Cat Lover Tropicals Plumerias
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drdawg
Feb 18, 2016 9:41 AM CST
Mine are commercially produced. I buy them 15-20 at a time and though they cost about a buck each, it is money well spent in my opinion.
drdawg (Ken Ramsey) - Tropical Plants & More
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If God wanted me to touch my toes, he would have put them on my knees.
Name: Crissy
Fallston, Maryland
CrissyJones
Feb 18, 2016 9:53 AM CST
Thank You! both.
I'm omw to purchase sand to place on top of the last 2 to 3 inches of soil. An older neighbor of mine said it prevents them from laying their eggs and also makes the plants pretty. She scolded me yesterday from her window when she saw all my plants outside on the deck...lol...She said it's too cold, take them back in NOW...Until I told her I had BUG METROPOLIS. ..hahahaha. She also mentioned putting a sliced potato in the soil to remove the larvae...Then throw the potato away. As you can see I'm willing to diligently try anything. I LOVE plants, but I can't stand bugs especially when they're in my house.
Name: woofie
NE WA (Zone 5a)
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woofie
Feb 18, 2016 10:07 AM CST
I tried the potato trick and it didn't work for me. However, putting about an inch of bird gravel on top of the soil definitely seems to work.
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Name: tarev
San Joaquin County, CA (Zone 9b)
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tarev
Feb 18, 2016 5:04 PM CST
I have my Pinguicula carnivore that attracts the fungus gnats when it is in its carnivore mode. But right now it is still in its non-carnivore mode, so I use the yellow sticky cards.

Other than that, got to lessen watering a bit so media does not stay too moist and gnat friendly.

Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
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RickCorey
Feb 18, 2016 5:04 PM CST
I put pine bark shreds on top of my seed-starting trays to keep the surface dry. I've never had gnats but I don't know whether the bark helped or maybe "I just don't have gnats". Wouldn't you think gnats could crawl under the bark layer to reach the moist mix?

I also avoid organic fertilizer and compost in my seedling trays. If your potting mix has organic components that decompose in the pot, that may be growing small amounts of fungus, hence attracting fungus gnats. The next time you re-pot, you might consider an indoor mix that is less prone to fungus, and drains fast enough to especially discourage fungus on the surface.

You might scraper an inch of mix off the top, and discard that along with any insect eggs. Then replace the top layer with something less organic and faster-draining.

If you do try peroxide, first test whether DILUTE peroxide is enough to discourage them.

Like 2 ounces of drugstore peroxide per quart of water. Or one cup per gallon. That gives a final strength of 0.2% peroxide.

(Drugstore hydrogen peroxide bottles have 3%. Food Service peroxide might be 20%.)
Name: Tiffany
Opp, AL (Zone 8b)
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purpleinopp
Feb 20, 2016 6:58 AM CST
Products containing BTi will get rid of the gnats. You put it in the water given to plants & it kills the larvae. Mosquito dunks & mosquito bits are 2 products that can be used for this.
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Name: Ken Ramsey
Starkville, MS (Zone 8a)
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drdawg
Feb 20, 2016 8:22 AM CST
Good information, Tiffany. I use the dunks in my outside rainwater tub and can easily crush up bits of it and use that solution along with the yellow sticky cards.
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Name: Tiffany
Opp, AL (Zone 8b)
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purpleinopp
Feb 20, 2016 9:09 AM CST
The yellow cards can trap adults. The adults lay eggs in the soil. They hatch into larvae that eat decaying organic matter (and roots if necessary.) Then they make a tiny cocoon & hatch into an adult. By killing the larvae in the soil, the cycle should be broken. Gnats don't have any connection to plants except to eat their roots if the roots are the most attractive organic matter in the soil in which they've been deposited.

Since gnats can fly, they can come in whenever a door is opened. Those who live where winter is cold should be able to treat plants once in the fall and be done with it. In a greenhouse or where it's warm enough for gnats to be active all year (and possibly fly inside on any warmish day,) periodic prophylactic treatments would be a plan to ensure there's never a serious infestation.
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[Last edited by purpleinopp - Feb 20, 2016 9:10 AM (+)]
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Name: Ken Ramsey
Starkville, MS (Zone 8a)
[url=www.tropicalplantsandmore.com]
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Composter Bromeliad Master Gardener: Mississippi Cat Lover Tropicals Plumerias
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drdawg
Feb 20, 2016 9:13 AM CST
I seldom have ever seen gnats in the greenhouses over the years. Perhaps natural predators are abundant enough to control them in those greenhouse settings. The solarium is a whole different ballgame. Most of the gnats are associated with my adenium plants. I know this because of the way the yellow cards load up with the gnats. I will make up that mosquito dunk mixture today and water all my potting media based plants with it.
drdawg (Ken Ramsey) - Tropical Plants & More
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Name: Tiffany
Opp, AL (Zone 8b)
Houseplants Organic Gardener Composter Region: Gulf Coast Miniature Gardening Native Plants and Wildflowers
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purpleinopp
Feb 20, 2016 11:19 AM CST
Interesting to hear! AFAIK, I don't have problems with potted plants while they are outside, but there can be a few gnats flying around when I first bring them in. Hard to say if it's from propping open doors, some window screens with holes, not enough of a "thing" to investigate. I don't use any peat in pots, so I haven't had any issues with ongoing infestation since getting rid of peat, even in pots that have ground dirt (for some plants that are only potted for a few months to overwinter.)
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Name: Ken Ramsey
Starkville, MS (Zone 8a)
[url=www.tropicalplantsandmore.com]
Orchids Greenhouse Vegetable Grower Ferns Region: United States of America Hummingbirder
Composter Bromeliad Master Gardener: Mississippi Cat Lover Tropicals Plumerias
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drdawg
Feb 20, 2016 12:35 PM CST
All my 1000 tropical plants go outside in March/April. I don't worry one iota about insects while they are outside. Until I started bringing plants into the solarium this fall, I really had no problem with gnats/white flies/scale. But since the solarium is a closed environment, there are no natural predators for those insects. I don't use a bit of peat but do use a lot of milled sphagnum moss in my terrestrial mixes.
drdawg (Ken Ramsey) - Tropical Plants & More
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If God wanted me to touch my toes, he would have put them on my knees.
Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
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Weedwhacker
Feb 20, 2016 3:48 PM CST
Great suggestion about using the mosquito dunks, Tiffany!
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Name: Gita Veskimets
Baltimore or Nottingham MD-212 (Zone 7a)
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gitagal
Feb 20, 2016 8:22 PM CST
DrDawg---
First of all--thanks for the acorns. You are so generous....

I talk to customers at my HD all the time about Fungus Gnats. People are trying to buy
all kinds of sprays to kill them. I have to educate them re FG's and what they should be doing.
Like- keeping their plants dryer (water from the bottom!) and doing whatever they can to take away
the Gnat's access into the potting Mix. All the above suggestions are good ones.
I have heard that once the Gnats cannot lay eggs in the soil--they only live about 2-3 weeks
and then are gone. So--let them fly around--and count the days....:o)

BTW--if you do not know where to buy the sticky pads--"Planet Natural" catalog has them as well as
the wire holders.

http://www.planetnatural.com/product/yellow-sticky-traps/

Gita

My deterrent is to treat ALL my plants 2 weeks before I bring them inside in the fall.
I still have half a jug of "Bonide Systemic Granules" and use that. Not the best...I know....
These are hard to find nowadays--Not sure they make them any more.

One thing that no one mentioned that can also be applied on top of the soil is "diatomaceous Earth"
Just be careful--it is powdered silica (glass) and you do not want to inhale it.
DE can also be used in the garden to deter slugs. They cannot crawl through the DE--as their soft
underbellies get all shredded.


Name: Tiffany
Opp, AL (Zone 8b)
Houseplants Organic Gardener Composter Region: Gulf Coast Miniature Gardening Native Plants and Wildflowers
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purpleinopp
Feb 21, 2016 8:42 AM CST
Since BTi does the job, using chemicals (especially a systemic) for fungus gnats is like using a gun to swat a fly. WAY more power than needed.

Imidacloprid is very controversial stuff. I don't want it in my yard, and definitely not in my house, especially if there is a completely organic way to address the issue.
http://npic.orst.edu/factsheets/imidagen.html
http://www.motherearthnews.com/nature-and-environment/enviro...
https://www.beyondpesticides.org/assets/media/documents/pest...

One can also just repot to get rid of them. Unpot the plant, rinse the old soil off of the roots, wash the pot if re-using to make sure there are no eggs stuck to it, replace plant with new soil.

If one is using a chunky mix, bottom watering isn't an option, the water won't wick up. Bottom watering can also lead to a build up to toxic levels in the soil of chemicals like fluoride, chlorine, and minerals like lime. If gnats can reach drain holes, they will lay their eggs there.
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Name: Ken Ramsey
Starkville, MS (Zone 8a)
[url=www.tropicalplantsandmore.com]
Orchids Greenhouse Vegetable Grower Ferns Region: United States of America Hummingbirder
Composter Bromeliad Master Gardener: Mississippi Cat Lover Tropicals Plumerias
Image
drdawg
Feb 21, 2016 9:42 AM CST
All the advice concerning (non-chemical) control of gnats is well-taken but let's be practical here. I have several hundred potted plants. Can you just imagine how long it would take me to re-pot every single one of them? And even then, what's the chances that there will still be eggs? I will continue to use my sticky cards but that's about as close to "natural" as I can come. In a month, the vast majority of them will be outside and that will take care of the problem, at least the problem having them inside the OPP.
drdawg (Ken Ramsey) - Tropical Plants & More
[url=www.tropicalplantsandmore.com]www.tropicalplantsandmore.com[/url]
If God wanted me to touch my toes, he would have put them on my knees.
Name: Tiffany
Opp, AL (Zone 8b)
Houseplants Organic Gardener Composter Region: Gulf Coast Miniature Gardening Native Plants and Wildflowers
Bulbs Foliage Fan Tropicals Butterflies Garden Sages Cactus and Succulents
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purpleinopp
Feb 21, 2016 10:09 AM CST
Agree, with a huge number of plants, repotting would be impractical. You're going to water them anyway, so the BTi in the water should be all that is needed.

http://www.motherearthnews.com/homesteading-and-livestock/bi...
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