UPDATE: Post 9: Mosquito Dunks & flies...help me remember

A year or two ago there was a thread about flies and someone mentioned using mosquito dunks, maybe in a sprayer? Can’t remember. Seems to me it was an accidental fly-repellant discovery.

Anyone remember the details? Or does anyone have any anecdotes about using mosquito dunks as premise fly control?

Black flies are the worst they’ve been here in several years. My normal fly control methods of the Country Vet misters in each stall and the aisleway and fly traps don’t seem to be putting as much of a dent in the fly population inside the barn as they normally do.


I remember someone putting them in a sprayer but I don’t remember if it worked on flies or gnats. I’ve thought about using it on the horses but have resisted the urge, for now. :smiley:

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Up front disclosure, I am a Master Gardener so not necessarily the best resource. Please do your own research.

Usually mosquito dunks contain a bacteria (Bacillus thuringiensis sap israelensis (Bti)) specific to mosquito larvae.

You could try using mosquito dunks for other insect species but they may not be effective unless their larvae can also be impacted by Bit.

I suspect using dunks for anything other than mosquito larvae control would be considered off-label and effective may be anecdotal or accidental.

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HAHAHA, that was me!

It’s not a repellent. It works where they breed, like your manure pile, and prevents them from developing. Yeah, I find it pretty effective! Started with spraying typical “fly breeding” places with mosquito dunk water every day, but now I just put a dunk in all water sources instead. I found a paper that evaluated treating the water with Bacillus thuringiensis serotype israelensis (aka mosquito dunks) in chicken houses to reduce fly load, and it was found effective. Yeah, chickens aren’t horses–but I have chickens, so started there.

If you have a lot of flies, sure, spray down your manure pile and any other areas where flies are breeding, and see if that helps! And drop a dunk in the water :smiley:

Don’t use it on the horses, though! Won’t hurt them, but it sure won’t actually DO anything.

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Ah-ha! Here are some of the poultry articles I ran across:

Bti sprayed on chicken manure significantly reduces house flies: https://pubmed.ncbi.nlm.nih.gov/19834080/

Another one that states “Adding Bti to chicken feed is potentially an efficient measure for the management and control of house flies in caged-poultry facilities.”: https://pubmed.ncbi.nlm.nih.gov/22182611/

(In case it was missed above, yes, I realize horses aren’t chickens, but I also have chickens, so started there. Spraying manure is universal across species :lol: and mosquito dunks have a looooong history of being used safely in livestock water.)

Flies and mosquitos are both dipterans, which is why this works. So yeah, it’s a pretty cheap and (kinda) easy way to make a dent in your flies. :slight_smile:

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@Simkie Thanks so much! That all makes sense. I will spray my manure cart and around the perimeter of my barn. I’m not tempted to spray the horses…lol. I’ll report back and let everyone know if I see a difference.


Bti will work for some fly larvae such as mosquitos, crane flies and fungus gnats.

Bti won’t impact the flying insects, only the larvae.



UCANR, University of California Agriculture and Natural Resources is one of my favorite resources.

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As the papers I linked above show, it’s not just mosquitoes, crane flies and fungus gnats. Other dipterans are also impacted.

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Update: I put half of a Mosquito Dunk in a 1.5 gallon sprayer full of water and let it sit for 2-3 hours Thursday midday. I sprayed Thursday afternoon, Thursday evening, Friday morning and evening, Saturday morning, and Sunday morning. I am spraying the floors of my three stalls, the feed room, and aisleway, and I’m spraying the doorway area at each end of the barn. I’m also spraying the manure cart, which is about 70’ from the barn. I skipped spraying the manure cart on Saturday. On Friday, I also brought the sprayer back to my house and sprayed around my back deck. The flies have been so annoying out there that you can’t even sit out there peacefully. I sprayed the barn area again this morning, Monday, and I’ll need to refill the sprayer tomorrow morning, so it looks like I’ll get about a week out of the mix if I’m spraying once a day.

Friday morning, I was surprised to find the fly population noticeably reduced when I went into the barn for morning chores. I thought it had to be a coincidence, a fluke. By Friday afternoon, after it had really warmed up and the sun was shining brightly and there were still no real flies to speak of, I became convinced it wasn’t a fluke after all.

When I did chores Saturday morning, I decided I’d try to count the flies. Yes, count them…as in there were so few I could count them. I counted five. This morning I counted four while doing chores. My barn is virtually fly free. It is amazing.

I didn’t tell my mom (who lives with me) that I had sprayed around the deck and around the house. I sat out there for about ten minutes Saturday evening and saw exactly one fly. I asked Mom how the flies were when she was out there. She thought a minute and replied that, come to think of it, she didn’t see any.

@Simkie Thanks for the info. I declare the Mosquito Dunk tea a great success!


Well, I posted an update and went back to edit it to add a thanks to Simkie, at which point it was flagged as potential spam. Anyway, thanks, Simkie! My barn is now a fly-free zone!

Wow, that worked fast! :eek: Awesome, so glad it helped!

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In my original update that is flagged, I explained the whole process. Basically, after spraying twice on Thursday, by Friday morning, I noticed a marked difference. By Saturday morning I was practically fly free. It’s like a Christmas miracle in June! I was skeptical on Friday because I couldn’t believe I’d see results so quickly (if I understood the article, it works on larvae, not adult flies). But something affected the fly population. Not a single fly in or around my manure cart—usually it’s covered. No flies—not one—on the fence rails where my fly traps hang. They’re usually covered in the vicinity of the traps as flies swarm to get in the trap. That cannot be a coincidence. Practically no flies at all in the barn. It’s crazy. I’ll take that kind of crazy.

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I wanted to reply earlier and kept forgetting to figure out where this post was.

I will confess I didn’t read your link ( :o ). I was researching a very similar question in a different context which I why I posted what I did. I “assumed” (which, I know, isn’t a good thing to do) that Bti would affect more than just the species I listed and would probably be useful against any species in the same genus.

I do hope you’ve had the chance to read the studies at the links :slight_smile: They are not long. It’s really pretty cool, and does seem to be a cheap and easy tool to add to the fly control arsenal.

Both links point to papers published in peer-reviewed journals. Pubmed is a great resource!

After 6 wk of application, house fly larvae decreased by 11% as a result of B. bassiana treatment alone, 41% for 250 mg.kg(-1) Bti alone, and 42% for 500 mg.kg(-1) Bti alone.

In the field, a concentration of 10 g Bti/kg of feed resulted in 90% reduction of larvae at 4 wk after treatment.

@Simkie as a big believer of IPM, I’m overall a big fan of biological controls as long as the user understands their use and impact :slight_smile:

Using Bti against say, caterpillars, that aren’t impacted by it isn’t ‘bad’ but not effective either :slight_smile:

Using liquid Bti wouldn’t be effective against everyone’s favorite hornworms (which can be controlled by Btk (Bacillus thuringiensis v kurstaki)). Btk will control many caterpillars, worms and borers. But those ‘caterpillars’ will grow into beneficial pollinators like butterflies and moths :slight_smile:

Well, yes, of course. The point is that bti is not limited in effectiveness to mosquitoes, crane flies and fungus gnats. There is literature demonstrating effect on flies. No one here has suggested using bti on caterpillars.

Hope you enjoy the papers! :slight_smile:

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I have never heard of them. I just googled them and sold in my local hardware.

It seems to come in a round solid form and another thing in liquid form.

I presume I want the liquid one?

I use the dunks. Fill up your sprayer, drop in the dunk, let it steep overnight, spray the next day. A dunk will last a long time (a month) before crumbling to nothing.

I also put a dunk in all water sources (troughs, chicken waterers, etc.)

Report back on how it works for you :smiley:

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Just went out there. 2:00 in the afternoon, mid-80’s, humid. Still not a single fly around the manure cart or the fly trap. One or two buzzing around the barn aisleway on the sunlit side, not even worth mentioning. I keep waiting to see if it’s a fluke and I’m going to be overrun (overbuzzed?) with flies again. It seems too good to be true!


What about gnats or biting midges?