Fungus Gnats Like It Spicy!

shllnzl Posts: 1,810 ✭✭✭✭✭

Well, it is fungus gnat hatching time again and this indoor gardener is at war again for the second year. I will flag the time of year in my calendar so I get a head start next year.

I had changed my purchased organic potting soil brand and my method for starting and nurturing seedlings. (At this point I have only 3 seedlings left.)

Both hatching years they seem to be launched from my largest pot that was not over watered. I did notice small flying insects buzzing my windows and doors plus flying into my face outside. I don't know if any overwintered in other plants or were sourced through open doors; I suppose it is possible that there were some eggs on purchased fruits or vegetables.

Last year the gnats emerged from and destroyed my onion plants. This year they are coming from my just established ginger plant -- so far the plant is alive and the precautionary sticky trap caught a lot of them. Seems like the buggers like spicy food.

Last year I lost several plants through the stress of fungus gnat treatment. I hope to do better this year.

Sticky traps are worth the nuisance IF you can keep plant leaves and cat parts from sticking to them. I have been using a small number of them since last year. Right now, I have very many of them in every plant location in my house. I hope I noticed the first trap right after the bugs launched.

The fungus gnats appear to take flight at night: I put new sticky traps in the ginger late yesterday afternoon and the trap was well populated this morning.

Note that the gnats are drawn to computer screens and grow lights. I have great hopes for the huge sticky trap located with my grow light and seedlings.

I will be watering all plants except orchids with Bt treated water until things are under control again (if that ever happens in the gardening world.)

My calendar already has a reminder for next year and I will start water treatments then.

And I am doing indoor gardening because I have yet to get a good plan to protect from the outside pests...


  • annbeck62
    annbeck62 Posts: 980 ✭✭✭✭

    @shllnzl What is Bt? I also have a problem with fungus gnats. If I bait the yellow sticky traps they work but if there is something else I can do I'll try it.

  • soeasytocraft
    soeasytocraft Posts: 237 ✭✭✭
    edited May 2021

    @shllnzl Good luck! And I feel your pain! I'm so frustrated because these pesky gnats came in the potting soil I purchased! I had no idea what to do about them! Your discussion here is helpful.

    @annbeck62 I had no idea what BT is either. Here is a link I found on Mother Earth News how-to-use-bt-pesticide-zw0z1304zkin But I still don't know how it works for our problem.

  • karenjanicki
    karenjanicki Posts: 947 ✭✭✭✭

    Oh my. That sounds dreadful :(. I only had a patio garden last year but it battled constant problems. I have never heard of these though....

  • shllnzl
    shllnzl Posts: 1,810 ✭✭✭✭✭

    @soeasytocraft @annbeck62 Bt will eventually put enough bacteria in the soil to poison the bellies of fungus gnat larvae and is also used for other caterpillar problems.

    Sticky traps are about the only way to control the adult gnats. I miss most of the ones I try to kill by clapping. Don't forget to place the traps near computer monitors and grow lights. Gnats are probably the small flying creatures spinning in a circle in the air that you can see in sunny spots in the yard.

    My sticky traps had lots more victims this morning, so it appears that the adult gnats take to wing overnight and/or in early morning.

    This is a difficult battle that I had hoped to avoid this year. I am stubborn enough to want plants in my house. Hopefully the gnats won't infest sink drains this year, as they will seek out possible fungus and mold anywhere.

  • annbeck62
    annbeck62 Posts: 980 ✭✭✭✭

    @shllnzl thanks for the link and explanation. Mine also seemed to start with some soil medium I got to use for growing microgreens indoors. It was a huge problem last summer. I used the sticky traps and somewhere read that pouring hydrogen peroxide on the soil killed the eggs so I did that too. I think the hydrogen peroxide helped but can't be certain. Over the winter the problem disappeared and I thought I was in the clear. Now that the weather is warming, they're coming back....uggh. So I'm open to other solutions.

  • shllnzl
    shllnzl Posts: 1,810 ✭✭✭✭✭

    @annbeck62 I would be afraid that hydrogen peroxide would kill soil bacteria and maybe sensitive plants.

    The eggs are in the potting soil most likely, yet I don't see hatching anywhere else. I will continue to monitor things and contemplate why my large pots with spicy contents are the source of my problems.

    Why are onions, and now ginger root some of their favorite foods?

    Why would deeper pots encourage them when the roots they are eating are within maybe 4 inches from soil surface? The soil around the ginger seemed to dry out fairly often and you are supposed to keep the soil moist, or so I have read. (This is my first attempt to grow ginger from a store root.)

    Can I keep the @#%^ bugs from laying eggs in other pots?

    I feel like a hunter/trapper as I patrol my traps several times per day.

  • shllnzl
    shllnzl Posts: 1,810 ✭✭✭✭✭

    I decided to try the hydrogen peroxide treatment on the ginger plant as it is the source of the gnats. I used one half cup of hydrogen peroxide (OTC strength) to a half gallon of water and have been using that to water the ginger. I was willing to sacrifice that one plant to save the rest.

    Knock on wood, I may have detected the beginnings of the invasion as I am not seeing too many now. I will continue to use the sticky traps and water with the Bt mix for at least another month. Hopefully things are getting under control. I will have to research the predicted hatching weather for the gnats.

  • Monek Marie
    Monek Marie Posts: 3,535 ✭✭✭✭✭

    If you can keep your soil drier it will help control gnats.

    None of these articles suggested it but I was wondering if something that covered the soil like small pebbles would help as gnats like to get in the soil. If it were harder to get in to the soil that might deter them.

    Also make sure your pots are very clean. When I worked in a greenhouse we had really bad gnat issues. We replaced some of the soil that was old in the greenhouse and also really washed and sterilized any pots and tools.