I'm having a hard time with fungus gnats again this year. Not as bad as winter 2018/2019, cause I still use the mosquito bits and yellow sticky traps. But I have a bunch of them and they are KILLING my seedlings!

Found out about this - Hot Shot 100046114 No-Pest Strip, Pack of 1 Price: $5.96 FREE One-Day. I'm glad I got it on Amazon, cause I was in my local hardware store later and saw the exact same item for 8.99!

Here is where I was reading about it. And even tho it's about aphids, it gave me the best ideas about how to use the product safely.
https://northernhomestead.com/...

And here.
http://insectsinthecity.blogsp...

Here is what I actually did. I popped the plastic covering open, cut the strip in half, put one piece each in small kitchen garbage bags with one seedling tray, twist tied them shut. Will this kill my seedlings? I don't know, but they're dying one by one anyway! And I don't even have half of them potted up yet! My precious (some of them expensive) seedlings!



I did this yesterday at noon. I'm leaving it for 24 hours. This is supposed to kill everything, except I don't think it will bother the eggs. So I gotta do it again in like 3 or 4 days!

Meanwhile, I'm researching this.
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Now I'm gonna go down there and see what happened.

The concern I would have, other than that dichlorvos is nasty stuff, is that it could be damping off disease that is killing the seedlings rather than the fungus gnats. Both damping off and fungus gnats thrive when plants are kept too damp, and enclosing the seedlings in plastic bags will increase the dampness. So if they are dying because of damping off then it would likely make it worse.

Since fungus gnats do their damage below the soil surface as larvae I don't know if the dichlorvos will reach them there as opposed to the flying adults, have you found some information on that?

We had fungus gnats on a plumeria plant that we overwintered in the kitchen. My husband put glue boards on top of the soil and then fitted a piece of styrofoam over the stem of the plant. They couldn't escape and eventually got stuck on the glue boards.

GardensAlive has a product called Knock-out Gnats. It works! It's some sort of BT and you use it as a soil drench so it kills the larvae. It won't kill the adults so definitely also use yellow sticky traps and you will most likely have to repeat it a couple of times before they all die. It costs about $25 for a bag of the stuff but unless you have a huge greenhouse it should last you a lifetime. I bought some years ago (maybe 10?) and still use it when I get an outbreak.

First, the bad news. I didn't smell anything when I took the bags off, and then I saw a tiny spider crawling along the soil. Then I saw a Box Elder bug and then I spotted an adult fungus gnat going about its business on the soil surface. So I don't think I accomplished a single thing.

But, the good news is, the seedlings look like they enjoyed the treatment!

Elena, I'm already using BT. I know it's helping, but not solving my problem.

Sooby there's no way it could be damping off disease. I always let the soil get dry. Most of these are big, robust seedlings and I'm only watering them once a week right now.

But, I'm catching adult fungus gnats on the yellow traps. What I have found some information on is that there is no correlation between damp soil and the proliferation of fungus gnats. They don't care about that - they'll eat your cactus roots too.

josieskid said:

But, I'm catching adult fungus gnats on the yellow traps. What I have found some information on is that there is no correlation between damp soil and the proliferation of fungus gnats. They don't care about that - they'll eat your cactus roots too.

Can you tell me where you found information that there's no correlation between damp soil and fungus gnat proliferation? It's a general recommendation that managing moisture levels can influence their population, including this in an article by an entomologist who specializes in fungus gnats:

"Moisture management and sanitation are important in reducing problems with fungus gnats in greenhouse production systems. The use of well-drained growing media and not over-watering plants may avoid issues with soil-borne plant pathogenic fungi, thus diminishing the possibility of disease transmission by the larvae and adult. The accumulation of water and presence of algae may lead to abundant populations of fungus gnats and thus damage to greenhouse-grown crops"

https://www.mdpi.com/2075-4450...

If you read further down the article there's an interesting comment about Bounce dryer sheets!

There's also this: "Substrate Water-Holding Capacity
We noticed that some substrates in our trial held more water than others with consistent watering. The soil moisture of the organic mixes was generally higher than in the conventional mixes, perhaps due to the use of compost and fewer aggregates (such as perlite) in some of them. In general, substrates that held more water produced more fungus gnats (Figure 4); however, this was not a hard and fast correlation with every substrate. Our assumption is that wetter substrates encourage the growth of the microbes on which the larvae feed."

https://www.greenhousegrower.c...

I had problems with this for varying degrees until I bought Gnatrol. My local garden place sells it in small bags for $20. It worked beautifully and was a very effective and natural control of them. You will see a big difference in your plants as the roots won't be chewed up and your plants will thrive.

magnolialover said:I had problems with this for varying degrees until I bought Gnatrol. My local garden place sells it in small bags for $20. It worked beautifully and was a very effective and natural control of them. You will see a big difference in your plants as the roots won't be chewed up and your plants will thrive.

Can you tell me what concentration you used, at what stage you applied it (at planting, when gnats appeared, etc) and how often? Trying to determine how much to buy. Thx so much. Also for those using Mosquito Bits.... i believe the strain of BTI is different for Gnatrol and so it may be more effective for fungas gnats (or perhaps its marketing.. who knows)

goedric said:

Also for those using Mosquito Bits.... i believe the strain of BTI is different for Gnatrol and so it may be more effective for fungas gnats (or perhaps its marketing.. who knows)

Gnatrol and Mosquito Drunks are both Bti, Bacillus thuringiensis suspecies israelensis.

with Tracey! My seedlings started to to grow beautifully after I applied Gnatrol. I used to get it from Amazon. Here is a pic of the packet of powder. You can see the instruction on it.

sooby said:

Gnatrol and Mosquito Drunks are both Bti, Bacillus thuringiensis suspecies israelensis.

Yes, but the strain and toxicity (to pests) are quite different:

Gnatrol for Fungas Gnats: Bacillus thuringiensis subspecies israelensis strain AM 65-52 solids, spores and insecticidal toxins 37.4%

Mosquito Dunks/Bits: Bacillus thuringiensis subspecies israelensis Strain BMP 144 solids, spores and insecticidal toxins 10.31%

kousa said: with Tracey! My seedlings started to to grow beautifully after I applied Gnatrol. I used to get it from Amazon. Here is a pic of the packet of powder. You can see the instruction on it.

Yes, but did you apply prior to seeing an infestation as a preventative of only after you had a problem? And do you have to repeat the treatment a month later or anything?

Thx!

Ok, I may have spoken too soon. I've gone down there twice this morning to look and not a creature is stirring! Maybe this product doesn't instantly kill? I am going to try the potato trick. The only potatoes I have are frozen french frys (crinkle cut), so we'll see!

I applied the solution to my seedlings after I saw infestation. I used the maximum as directed on the package because my seedlings were in distress. I applied every 4 days the first 2 weeks. After that, I only applied if I saw an infestation again. By that time, the seedlings were much stronger from being able to grow during the 2 weeks of treatment and after that most gnats were eliminated to continue to do anymore damage. One packet like above was more than enough to handle 200 seedlings. I might have overdone it with the application though. You may get even more use out of the packet.

I used mosquito dunks first with little to no response.

Because my infestation was out of control, I started with just under a tablespoon per gallon per week. Within the month I was able to decrease to a teaspoon or so and as I saw next to none. I use that amount now as a maintenance dose to keep them gone.

Do you have to use the gallon mixture immediately, or will it keep for future use?

I 90% of the time use it all at once. If you use the half gallon, just half the dose. Better to use immediately as I understand it.

Mary thanks for starting this subject. I got proactive and purchased a four ounce pack of Gnatrol. My plan is to use it before any signs of infestation.
Mary or anyone that want to chime in, what type of soil do you start your seeds in ?

I have also ordered gnatrol, off Ebay. I feel that this will work, but the plants must be isolated as much as possible, to avoid gnats coming from other parts of the house to re-infest. I am going to get zip-able covers for my shelving.

I was also advised by Runningfox on the LA that SCAN MASK nematodes will work on an active infestation. I think this is more difficult because the nematodes are expensive and have a short shelf life. But I might do it if I have to.

Last year I had a terrible time with the gnats.

I tried Mosquito Bits, used them consistently, and they did not work, though they supposedly contain BTI. I tried that glass-based sharp sand to top off the pots, it did not work and cut up my hands. I ended up repotting all the ones I used it on. I tried sprays, which did not work. I finally ended up dusting regularly with diatomaceous earth, which worked somewhat, but coated everything in the room with white, gritty dust.

I am also considering baking the seedling mix before use, to eliminate soil-borne gnats. Seems like a lot of bother, but the gnats last year were insane!