Fungus Gnats

User avatar
GoDawgs
Reactions:
Posts: 3742
Joined: Thu Dec 12, 2019 6:38 am
Location: Zone 8a, Augusta GA

Fungus Gnats

#1

Post: # 34471Unread post GoDawgs
Mon Nov 23, 2020 6:59 am

I'm playing indoors with micro cherry tomatoes this winter. These three were started Oct 30 and when I checked yesterday the roots weren't quite to the bottom of the pots yet. They will eventually be transferred to a one gallon pot. Lille Lisa and Red Robin are red and Jochelos is a deep yellow.

Image

There have been fungus gnats out and about on these and the two broccoli plants I have coming along. The plants probably had not been allowed to dry out enough between waterings. My bad. I thought I remembered reading about hydrogen peroxide spray as a treatment so I looked it up. Yep. One part regular 3% peroxide to three parts water so that's what I mixed up and put in a little spritzer bottle. I know it's probably been discussed before but I'm posting this in case there are new folks who have joined who might have missed any previous posts.

Image

Peroxide won't hurt the plants at all. The pot's soil surface and the plants themselves need to be sprayed daily for ten days, as that's the fungus gnat life cycle. By the end of 10 days any eggs in the soil will have hatched with newly hatched gnats having come to the surface to meet their doom. The treatment worked like a charm. They're gone.

There was also one tip on telling the difference between fungus gnats and fruit flies: fungus gnats are slow and easy to grab but fruit flies are a whole lot quicker. Quicker than I am! That's got me wondering if peroxide spray will also work on fruit flies that, from time to time in warmer weather, may invade the small compost bucket I keep by the sink. We'll see.

User avatar
Labradors
Reactions:
Posts: 676
Joined: Tue Dec 10, 2019 3:38 pm
Location: Ontario, Canada

Re: Fungus Gnats

#2

Post: # 34472Unread post Labradors
Mon Nov 23, 2020 7:05 am

Interesting to know!

I read somewhere quite recently that pouring boiling water over the sterilized potting mix will kill any fungus gnat eggs. That could be a handy thing to try if you know you have some infected potting mix! Not only that, but boiling water also makes it absorb the water much faster than cold (except that you have to wait for it to cool down before planting anything).

Linda

User avatar
brownrexx
Reactions:
Posts: 2079
Joined: Thu Dec 12, 2019 1:05 pm
Location: Southeast PA, zone 6b

Re: Fungus Gnats

#3

Post: # 34473Unread post brownrexx
Mon Nov 23, 2020 7:58 am

I put my potting soil / soiless mix outside in the freezing temperature for a couple of days before I use it in the spring and I very rarely see fungus gnats. I use the freezer if it is not cold enough outside.

If I get fungus gnats, I put part of a Mosquito Dunk in my watering can and water with that.

User avatar
pepperhead212
Reactions:
Posts: 3106
Joined: Mon Jan 20, 2020 12:07 am
Location: Woodbury, NJ

Re: Fungus Gnats

#4

Post: # 34474Unread post pepperhead212
Mon Nov 23, 2020 8:00 am

I always put some Bt israelensis in both my soil, and hydroponics setups, to prevent fungus gnats.
Woodbury, NJ zone 7a/7b

User avatar
AZGardener
Reactions:
Posts: 761
Joined: Wed Dec 11, 2019 9:12 am
Location: Arizona, USA

Re: Fungus Gnats

#5

Post: # 34475Unread post AZGardener
Mon Nov 23, 2020 8:38 am

I also use boiling water with my seed mix and have no issues until the seedlings start going outside to harden off. When the gnats show up, I treat with gnatrol (active ingredient Bt israelensis). I've tried other methods (apple cider vinegar, cinnamon, sand) and have had the best results with boiling water and Bt. HTH
USDA Zone 9b, Sunset Zone 13
Average Rainfall 9.5 inches
Climate: Sonoran Desert

User avatar
brownrexx
Reactions:
Posts: 2079
Joined: Thu Dec 12, 2019 1:05 pm
Location: Southeast PA, zone 6b

Re: Fungus Gnats

#6

Post: # 34479Unread post brownrexx
Mon Nov 23, 2020 9:50 am

Bt israelensis is what Mosquito Dunks and Mosquito Bits are composed of. They kill the larvae not the adults.

User avatar
GoDawgs
Reactions:
Posts: 3742
Joined: Thu Dec 12, 2019 6:38 am
Location: Zone 8a, Augusta GA

Re: Fungus Gnats

#7

Post: # 34481Unread post GoDawgs
Mon Nov 23, 2020 10:05 am

Fortunately I've not had fungus gnat problems before but it's good to know about the boiling water and bT Is., etc for infected potting soil mix.

User avatar
pepperhead212
Reactions:
Posts: 3106
Joined: Mon Jan 20, 2020 12:07 am
Location: Woodbury, NJ

Re: Fungus Gnats

#8

Post: # 34495Unread post pepperhead212
Mon Nov 23, 2020 3:56 pm

brownrexx wrote: Mon Nov 23, 2020 9:50 am Bt israelensis is what Mosquito Dunks and Mosquito Bits are composed of. They kill the larvae not the adults.
That's where you have to attack them - a preventative measure like that. I do this with my large plants I bring inside, about 2 weeks before bringing them in - one of the major sources of indoor fungus gnats. There are always some larvae in the upper 2" or so of the plants outside, unless treated on a regular basis.
Woodbury, NJ zone 7a/7b

User avatar
bower
Reactions:
Posts: 5475
Joined: Thu Dec 12, 2019 12:44 pm
Location: Newfoundland, Canada

Re: Fungus Gnats

#9

Post: # 34504Unread post bower
Mon Nov 23, 2020 6:59 pm

I had a plague of fungus gnats on the indoor plants until I discovered Bt-i (mosquito dunks or bits). Yes it is tricky to deal with adults, and perhaps the peroxide is best for that. We tried a combo of yellow sticky traps near the soil for adults along with mosquito dunk in the watering can for the larvae, but it was not a 100% solution in that season. The year after, a pre-emptive strike with the mosquito dunk watering has completely prevented any gnats from emerging. I would do that again for any plan like, growing peppers to maturity in the house. They are such magnets for trouble anyway (aphids!), but the fungus gnats ate their little roots and really caused them a sad time.
AgCan Zone 5a/USDA zone 4
temperate marine climate
yearly precip 61 inches/1550 mm

User avatar
pepperhead212
Reactions:
Posts: 3106
Joined: Mon Jan 20, 2020 12:07 am
Location: Woodbury, NJ

Re: Fungus Gnats

#10

Post: # 34514Unread post pepperhead212
Mon Nov 23, 2020 9:35 pm

Here is the Bt israelensis that I use. It is a liquid, which only takes 8 drops per gallon of water (I use filtered water, since Cl might kill the bacteria), to either moisten the seeding mix I use, or to moisten the pots, before bringing them in. The mosquito dunks I use small pieces of, in my hydroponics, and SUVs. I never see a fungus gnat indoors any more! The liquid stays active for 2 year at room temp, according to the company, but I keep it on the door of my fridge, anyway.
Woodbury, NJ zone 7a/7b

User avatar
MissS
Reactions:
Posts: 5599
Joined: Fri Dec 13, 2019 4:55 am
Location: SE Wisconsin Zone 5b

Re: Fungus Gnats

#11

Post: # 34515Unread post MissS
Mon Nov 23, 2020 9:39 pm

Granular diatomaceous earth placed as a topping on the soil will also control fungus gnats. If you use mycorizae in your soil then avoid using the hydrogen peroxide. It will kill them.
~ Patti ~

User avatar
Nan6b
Reactions:
Posts: 1545
Joined: Tue Dec 10, 2019 2:58 pm
Location: Pittsburgh, PA

Re: Fungus Gnats

#12

Post: # 34569Unread post Nan6b
Tue Nov 24, 2020 6:55 pm

The DE helped where everything else failed, for me.

User avatar
GoDawgs
Reactions:
Posts: 3742
Joined: Thu Dec 12, 2019 6:38 am
Location: Zone 8a, Augusta GA

Re: Fungus Gnats

#13

Post: # 34612Unread post GoDawgs
Wed Nov 25, 2020 12:29 pm

I have food grade DE down in the shed so I can try some of that. The feed 'n weed probably has mosquito dunks this time of year. Everybody else has cleared the garden center and stuffed it with Christmas.

User avatar
Amateurinawe
Reactions:
Posts: 1484
Joined: Wed Jul 08, 2020 1:11 am
Location: Emsworth UK

Re: Fungus Gnats

#14

Post: # 34616Unread post Amateurinawe
Wed Nov 25, 2020 1:03 pm

Same here [mention]GoDawgs[/mention] I went last weekend to the local garden centre and it was full of glitter, trees, christmas lights and I couldn't find half the stuff I wanted. So i got some manure quick and got outta there.
The behaviour of light means you observe me as i was then, and not as I am now.
I cannot change history, so I do hope i gave you a good impression of myself

User avatar
brownrexx
Reactions:
Posts: 2079
Joined: Thu Dec 12, 2019 1:05 pm
Location: Southeast PA, zone 6b

Re: Fungus Gnats

#15

Post: # 34646Unread post brownrexx
Wed Nov 25, 2020 6:47 pm

I purchase food grade DE at Tractor Supply because people use it in chicken coops. I actually use it there too as it kills bird mites that get into the cracks and crevices of the coop.

User avatar
Cole_Robbie
Reactions:
Posts: 1432
Joined: Tue Dec 10, 2019 11:58 pm

Re: Fungus Gnats

#16

Post: # 34660Unread post Cole_Robbie
Thu Nov 26, 2020 1:50 am

Skeeter dunks.

User avatar
GoDawgs
Reactions:
Posts: 3742
Joined: Thu Dec 12, 2019 6:38 am
Location: Zone 8a, Augusta GA

Re: Fungus Gnats

#17

Post: # 35359Unread post GoDawgs
Mon Dec 07, 2020 11:01 am

I found the skeeter dunks today at my feed & seed. Now, how big a piece of the dunk to how much water? I just need to make up about a pint of it.

User avatar
pepperhead212
Reactions:
Posts: 3106
Joined: Mon Jan 20, 2020 12:07 am
Location: Woodbury, NJ

Re: Fungus Gnats

#18

Post: # 35360Unread post pepperhead212
Mon Dec 07, 2020 11:22 am

[mention]GoDawgs[/mention] With that, you'd probably have better success with grinding it up, and mixing it in the upper 2" or so of soil in a pot (or, all of the soil mix, if starting a pot, or seed starting pots. It doesn't take much - they sell similar items for a lot more than the dunks, when you figure out cost per ounce, and they don't call for much. I remember many years ago the company that I originally got the liquid Bt is. from switched to the granular, and it was only about 4 oz, for almost $20 (supposedly made 100 gal, to water with), so I found the liquid elsewhere. But the dunks would work fine.
Woodbury, NJ zone 7a/7b

User avatar
AZGardener
Reactions:
Posts: 761
Joined: Wed Dec 11, 2019 9:12 am
Location: Arizona, USA

Re: Fungus Gnats

#19

Post: # 35415Unread post AZGardener
Tue Dec 08, 2020 5:53 am

I just wanted to add that using skeeter dunks or any of the other Bt products kills the larvae, not the adults, eggs, or pupa.
So, it may take 2 or 3 doses to get rid of them. But it works better than anything else I've tried, and I think I've tried
about all of the methods google searches can bring up. :D
USDA Zone 9b, Sunset Zone 13
Average Rainfall 9.5 inches
Climate: Sonoran Desert

User avatar
brownrexx
Reactions:
Posts: 2079
Joined: Thu Dec 12, 2019 1:05 pm
Location: Southeast PA, zone 6b

Re: Fungus Gnats

#20

Post: # 35417Unread post brownrexx
Tue Dec 08, 2020 7:28 am

A whole dunk controls hundreds of gallons of water so I just crumble a small amount into my watering can. Lots of solids will fall to the bottom but those are probably just fillers.

Post Reply

Return to “Diseases, Pests & Cures”