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Fungus Gnat Invasion


rabblemire

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Coming to you live from the frontlines....

I must have had a particularly nasty batch of soil, because I'm dealing with more gnats than I thought possible. It's currently week 4 of watering with neem oil drenches and the occasional spritz of Eight spray. Does anybody have any suggestions on how to combat these buggers? I'm going about 8 days between watering to let the medium dry but the population continues to grow.

 

 

Zone 8a

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Fungus gnats are infuriating!  

I've had luck with Steinernema feltiae nematodes

Then breaking up a Bt mosquito pellet, letting it soak for 30 minutes and watering the plants with that water.

Also Azamax drench, which is probably just the same as neem oil.

I applied the Bt and nematodes together, and then the azamax drench a week or two later, and kept alternating.

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@rabblemire What size pot or pots are you dealing with them ? I had a 20g kentia palm growing indoors and had the largest infestation of gnats. The palm got kicked out of the house and banished to the garage where it now resides. I used a product called gnat nix  by growstone which disrupts the life cycle of the gnats and is still working to this day. It's basically a layer of stuff that looks like floor dry or oil absorbent. 

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T J 

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I have tried just about everything to kill these nasty little pests including neem oil soaks, and almost daily sprays to keep them at bay, fly/gnat sticky strips nearby, DE powder, letting the soil dry for 2 week at a time, and hydrogen peroxide baths. 

Im on my last rope with these guys, so if you find some miracle treatment PLEASE share! 

 

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I had a large infestation. I put sticky yellow traps around each pot and watered the plants with the below granules soaked in the water, it has gotten rid of them. I left the granules in the water when watering and left them to sit on the soil to continue to release. Got them from Amazon. I know it says Mosquito but works for the gnats too. Take a few weeks to work though as it kills the larva not the gnat, so you need the traps to go along side them.

Summit...responsible solutions Mosquito Dunks 116-12 8-Ounce Quick Kill Mosquito Bits

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Not much you can do in the middle of winter but anytime you have severe fungal gnat infestations, you are probably watering too much and too often. Plus, your soil mix is too dense and doesn't drain properly but stays soggy/mucky. Those conditions encourage gnat infestations and promote root rot. Back way off on watering to give the soil a chance to dry out. In cold weather inside dark houses, palms don't need frequent watering and should stay on the dry side. Never let pots sit in trays of water. If the soil is moist, hold the water.

Come spring, I suggest you repot the afflicted plants in new, loose, free-draining mix in new or disinfected pots. Make sure those pots are not too large for the roots. Then monitor your watercan usage. Overwatering kills more palms than underwatering.

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Meg

Palms of Victory I shall wear

Cape Coral (It's Just Paradise)
Florida
Zone 10A on the Isabelle Canal
Elevation: 15 feet

I'd like to be under the sea in an octopus' garden in the shade.

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On 1/4/2020 at 12:47 PM, troposphere said:

Fungus gnats are infuriating!  

I've had luck with Steinernema feltiae nematodes

Then breaking up a Bt mosquito pellet, letting it soak for 30 minutes and watering the plants with that water.

Also Azamax drench, which is probably just the same as neem oil.

I applied the Bt and nematodes together, and then the azamax drench a week or two later, and kept alternating.

Thank you so much for the suggestions!  Where does one purchase Steinernema feltiae nematodes?

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  • 3 weeks later...

Lots of good advice already.
A layer of neem seed meal can work wonders. DE works also but you can’t top water. 
Good luck sir!

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I've managed to control minor gnat infestations by placing a small dish of apple cider vinegar next to the infected plant.  They end up getting stuck in the liquid and die. Perhaps that would work best in the early stages of infestation. And I do recall them affecting plants where the soil stayed wet.

@TNAndy I'm from Knoxville - where are you from?

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Jon Sunder

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Watering your plants with hydrogen peroxide mixed with water will kill the fungus gnat larva that are in the soil. 

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@rabblemire and to anyone else still interested:

Garden Safe Houseplant and Garden insect killer has solved my problem. 

I have sprayed the leaves, and soil surface with this moderately and had a 99.9% immediate reduction.

The 1 or 2 stragglers left have since died. I have not seen any ill effects to any plants that it was applied to which include:

Syngonium

Rabbit foot fern

Fittonia 

Tradescantia

Pothos 

Chlorophytum

Croton

Heliconia psittacorum 

Zingiber spectabile

Senecio serpens 

Echeveria runyonii

Sabal palmetto

Costus woodsonii

Aphelandra sinclairiana

Crown of thorns

Bismarckia nobilis

etc... 

 

 

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  • 2 weeks later...

Thank you everybody for all of this fantastic advice. It took a while but I was able to significantly reduce the infestation with a combination of Mosquito Dunks, sticky paper, a layer of coarse sand on top, a barrier over the drainage holes and watering from the bottom.

 

Unfortunately, two of my parlor palms did not make it. There was a sudden, rapid decline in which the trunks blackened and fronds drooped. My guess is that the soil I mixed up was indeed to dense and water retentive, like @PalmatierMeg suggested. 40% turface 60% pine bark mulch. I'll need to try again in the spring, assuming the others make it.

Zone 8a

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You can also try these predator. 

Robust predatory mite

What is Hypoaspis-System?

  • The brown and robust predatory mite Stratiolaelaps scimitus(Hypoaspis miles)
  • Inhabits the top layer of soil
  • Feeds on harmful soil-dwelling pests such as thrips pupae, fungus gnats larvae and larvae of shore flies
  • Easily survives without prey for several weeks

https://www.biobestgroup.com/en/biobest/products/biological-pest-control-4463/beneficial-insects-and-mites-4479/hypoaspis-system-4663/

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No need for fancy remedies, fungus gnats are the result of too much water in the medium.  The yellow sticky traps are very helpful, also.  :)

Rabblemire, Welcome to Palmtalk !

San Francisco, California

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