User avatar
TomatoNut95
Greener Thumb
Posts: 929
Joined: Sun May 26, 2019 3:11 pm
Location: Texas Zone 8

How do you kill gnats on houseplants?

Is there anything I can spray or sprinkle on the soil of the houseplants to kill the gnats or at least stop them from breeding in the soil? There are WAY too many gnats in this house! I've got some DE, will that work?

pepperhead212
Greener Thumb
Posts: 1434
Joined: Wed Oct 15, 2014 5:52 pm
Location: Woodbury NJ Zone 6B

Re: How do you kill gnats on houseplants?

The way I prevent the fungus gnats, once I bring plants back inside, or when I'm starting seeds, is to moisten the soil with a solution of Bt israelensis - this kills the larvae, so it's a preventive measure, and I start watering the plants a few weeks before bringing them inside, or wetting the mix when filling the seedling pots, with some of the solution. Once they are inside, I water them occasionally with the solution.

Since you already have the gnats, you have the larvae for sure, but to get rid of the adults, you can use some sticky traps, though they are fairly short-lived. Killing those larvae will keep them from coming back. The stuff I use is Microbe Lift, which is sold for killing mosquito larvae in ponds, but works for these, as well. Those "Mosquito Dunks" have the same type of Bt in them, and can be ground up and mixed into the soil, though I don't know how long this lasts.

Some people say that cinnamon mixed into the upper layer of soil will keep them away, but that doesn't help if the larvae are there already. And watering with a hydrogen peroxide solution may kill the larvae, but you'll have to find out how much to dilute it - I've never tried that, so I don't know.
Dave

User avatar
TomatoNut95
Greener Thumb
Posts: 929
Joined: Sun May 26, 2019 3:11 pm
Location: Texas Zone 8

Re: How do you kill gnats on houseplants?

Thanks, @Pepperhead! I've heard of bt, but not sure where to get it. Oh, and the houseplants stay inside. I don't move them out during the non-winter months.

pepperhead212
Greener Thumb
Posts: 1434
Joined: Wed Oct 15, 2014 5:52 pm
Location: Woodbury NJ Zone 6B

Re: How do you kill gnats on houseplants?

Here's the stuff that I get.
https://www.amazon.com/Ecological-Labs- ... ljaz10cnVl

It is not the Bt you use for most insects in the garden, like you find in Thuringer. That won't help against these or mosquitos. And as you can see in the Q&A that others use this for fungus gnats - 6 drops/gal. Not necessary to use every time, but in the beginning, until they seem to be gone. I keep that bottle in the fridge, and one bottle lasts me over 2 years. The label says it lasts for 2 years at room temp, but I have a shelf on one door of my fridge that I keep that, and other similar things with.
Dave

User avatar
TomatoNut95
Greener Thumb
Posts: 929
Joined: Sun May 26, 2019 3:11 pm
Location: Texas Zone 8

Re: How do you kill gnats on houseplants?

Awesome; I'll have to get some of that!! Thanks, @Pepperhead!! :) :)

User avatar
applestar
Mod
Posts: 27483
Joined: Thu May 01, 2008 11:21 pm
Location: Zone 6, NJ (3/M)4/E ~ 10/M

Re: How do you kill gnats on houseplants?

Once you get some Bti you might try this as well. Also as described — in the linked thread I think — I find fungus gnats adults will readily drown themselves in shallow containers of soapy water — I use Chinese food takeout containers.

Subject: Fungus Gnats
applestar wrote:I had an epiphany! It’s so simple I can’t believe It hadn’t occurred to me in all the years I’ve been using Bti — mosquito larvae and fungus gnat control — in the water.

The other day, I was watering my indoor plants with Mosquito-bits (Bti) infused water to control the fungus gnats larvae and giving them their daily morning thorough misting of filtered water with the spray bottle. There had been an upsurge in the fungus gnats since weather warmed up, and they were swarming all over the plants and potting mix surfaces. ...I was wishing I had something to get them midair when I could see them so clearly, but I was pouring effective control against them in a stream and spraying totally useless plain water in the air where they were flying....


Then :idea:) :idea: light bulb moment!!! ... I put a small amount of mosquito bits in the spray bottle, made sure the sprayer tube had the filter end on the inside and put it in, shook and let infuse for a while, then proceeded to spray everything with the Bti treated water — I sprayed the gnats in the air, the potting mix surfaces, surface of the plants, especially stems near the bottom, but top surfaces, too... outside surface of containers and rims, shelf surfaces... everywhere that the gnats would come in contact.

You see — Bti is a bacteria specific to mosquitoes and fungus gnats. I just have to infect the gnats — how many times have you watched those anti-bacterial soap and germicidal lotion commercials highlighting the door knobs, elevator buttons, toilet seats where there are germs you don’t want to touch? With some luck, they will pass it on to their eggs and infect the larvae as well. The bacteria needs moisture to stay alive but presumably will live on once inside the organism.

— 2 days later and all those gnats are practically gone. I think the rare ones I see flying are the ones that had been pupae and hatched out. I’ll spray with the Bti infused water a couple more times to break their life cycle and that should be that.
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.

User avatar
TomatoNut95
Greener Thumb
Posts: 929
Joined: Sun May 26, 2019 3:11 pm
Location: Texas Zone 8

Re: How do you kill gnats on houseplants?

Awesome! Wonder if that stuff works on hornworms. Just found two more in my garden today!!! :(

imafan26
Mod
Posts: 11118
Joined: Tue Jan 01, 2013 1:32 pm
Location: hawaii, zone 12a 587 ft elev.

Re: How do you kill gnats on houseplants?

If you have fungus gnats, you probably have rotting roots that the fungus is growing on and that in turn feeds the fungus gnats.
I would repot. Cut out the dead roots if the plant can be salvaged. Repot, and get rid of the saucer. Plant should be watered in the sink or the tub and drip dry. It is best if you have enough air circulation to dry out in 3 days. You may need to use a drier mix to accomplish that. If it takes more than a week for the plant to dry out, then add a fan or take the plant out if you can at night. Make sure you are not over potted.

Otherwise consider something like pothos that you can grow in a vase of water. Just change the water (use distilled water) and wash the vase weekly and you can add some dilute water soluble fertilizer. Dust the leaves. It still likes to have some light from a window. Add a piece of mosquito dunk to the water or BT.
Happy gardening in Hawaii. Gardens are where people grow.

User avatar
rainbowgardener
Super Green Thumb
Posts: 25303
Joined: Sun Feb 15, 2009 11:04 pm
Location: TN/GA 7b

Re: How do you kill gnats on houseplants?

Fungus gnats need water. The easiest way to get rid of them is to let the top few inches of the soil dry out thoroughly. Personally I think most people water house plants way more than they need to. I tend to water mine about every other week and mist the leaves in between and I never see fungus gnats.

When I do indoor seed starting, I have more trouble because the seeds have to be kept moist. I put cinnamon in the water I use to water them with. It doesn't work instantly, because it doesn't really kill the gnats, it kills the fungus in the soil that the gnats eat. That's why it has to be in the water, so it can penetrate the soil layers. Over time it is very effective.
Twitter account I manage for local Sierra Club: https://twitter.com/CherokeeGroupSC Facebook page I manage for them: https://www.facebook.com/groups/65310596576/ Come and find me and lots of great information, inspiration

  • Similar Topics
    Replies
    Views
    Last post

Return to “Organic Insect and Plant Disease Control”