Farnam SimpliFly with LarvaStop

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3 3/4lb


Oversold. Est. In Stock by 07/30/2019.



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Product Summary:

Farnam® SimpliFly® With LarvaStop™

SimpliFly® with LarvaStop™ is a highly palatable feed additive that prevents formation of fly larvae in treated manure. LarvaStop™ breaks the fly lifecycle by preventing the formation of fly larvae’s exoskeletons when they molt, resulting in their death. The alfalfa-scented pellets are easily fed and economical to use, and only need to be administered during fly season. Because the dosage is designated by weight, it can be given to any horses from minis to draft. A reduced risk pesticide, it contains no organophosphates and can be used as part of an integrated pest management program.


  • Prevents the development of stable flies and house flies in the manure of treated horses
  • Feed-thru fly control
  • Highly palatable feed additive
  • Contains no organophosphates
  • Pellets with an Alfalfa scent
  • Reduces fly populations by 97-100%
Item Specifications:

Active Ingredient:
Diflubenzuron (Dimilin) CAS# 35367-38-5 0.24%
Other Ingredients: 99.76%

Directions for Use:
Feed the recommended dosage each horse separately to make certain full portion is received. This product should be fed top dressed on grain or mixed with the horse's total ration to provide 6.8mg of diflubenzuron per 100 lb. of body weight. For an occasional finicky eater who does not accept new feeds readily, mix this product with sweet feed or grain ration.
Start feeding early in the spring before flies begin to appear and continue feeding throughout the summer and into the fall until cold weather restricts fly activity. This product contains an insect growth regulator that prevents the development of house flies and stable flies in the manure of treated horses, but is not effective against existing adult flies.
In some cases, supplemental fly control measures may be needed in and around paddocks and buildings to control adult house and stable flies that can breed in other decaying vegetable matter or silage on premises, or that migrate in from other areas.
SimpliFly™ with LarvaStop™ should be used as part of an integrated pest management program aimed at reducing fly populations in the horse's environment. Consult your retailer for program recommendations. In order to achieve optimum fly control, this product should be used in conjunction with other premise and on-animal products as well as good management and sanitation practices.

Daily Dosage:
300-500 lb. horse, pony or miniature horse: Feed 2/5 oz. per horse per day (one measuring cup filled to the blue line)
500-700 lb. horse or pony: Feed 3/5 oz. per horse per day (one measuring cup filled to the red line)
700-900 lb. horse: Feed 4/5 oz. per horse per day (one measuring cup filled to the green line)
900-1100 lb. horse: Feed 1 oz. per horse per day (one full measuring cup)
1100-1300 lb. horse: Feed 1 1/5 oz. per horse per day (one full measuring cup plus one measuring cup filled to the black line)
For larger horses over 1,300 lb. of body weight or draft horses, feed an additional 1/5 oz. for each additional 200 lb. of body weight.

It is a violation of Federal law to use this product in a manner inconsistent with its labeling.

Do not contaminate water, food or feed by storage or disposal. Store in original container in a cool dry place inaccessible to children and pets.

If empty: Do not reuse this container. Place in trash or offer for recycling if available.
If partially filled: Call your local solid waste agency or call 1-800-CLEANUP for disposal instructions. Never place unused product down any indoor or outdoor drain.

Downloadable Resources
Product LabelManufacturer Information
MSDS SheetManufacturer Information
Dosage and Feed InstructionsManufacturer Information
Style Item Number Model Number UPC
10lb SLT101621 010 100515883 086621001657
20LB SLT101621 020 100515884 086621001664
50lb SLT101621 050 100515885 086621001671
3 3/4lb SLT101621 375 100515881 086621047921

Product Reviews by Customers

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Browse 33 questions Browse 33 questions and 210 answers
Why did you choose this?
Statelinetack.com Store
The horses like it.
ELIZABETH P on Jul 9, 2019
it works
Chris B on May 10, 2019
The horses like it.
ELIZABETH P on Jul 9, 2019
Works great.
Audrey S on Jun 6, 2019
it works
Chris B on May 10, 2019
I chose this because it absolutely works! I've been feeding this to my gelding for the last 5 years now and am completely satisified with the results.
Tara S on Apr 28, 2019
This works well to curb the fly population during the spring/summer months.
Jennifer R on Apr 19, 2019
Great price and it reduces flys in barn.
Angie B on Apr 17, 2019
I've used this for several years and it really makes a difference in the presence of flies. The 20 lb size will last for my two horses most of the summer and the pricing was the best I could find online, including free shipping.
NIKKI L on Mar 17, 2019
Comments from others were positive.
Patricia C on Mar 15, 2019
really helps keep flies under control at my barn. I'm in the Houston area and I start it in March and continue through November with Simplifly. I have no equines/bovines boardering the property, so it works. Remember, all horses need to get it for it to work effectively. Easy to add to their feed. Been using it for years.
Roseann B on Mar 6, 2019
I use it every year! :)
Cindy C on Feb 18, 2019
After using this product for a couple of months we noticed a drastic decrease in our fly population and being in South Florida thats saying alot. I love it!
Stacey C on Dec 4, 2018
It works very well.
debbie c on Nov 24, 2018
Hoping this product stops the flies at the larval stage. Flies are a real aggravation.
Karen K on Oct 27, 2018
I've been using this year-round for about 20 years. It really works!
Mary T on Sep 22, 2018
because it really works
Jacquelyn P on Sep 5, 2018
Been using this for several years. We have hardly any flies at our barn.
Rusty H on Aug 22, 2018
works great to reduce flies.
Mariah M on Aug 19, 2018
Been using it for years! Keeps the flies at bay!
Susan L on Aug 19, 2018
It works
Amy E on Aug 17, 2018
This is awesome!!! Had a really bad fly problem on my two donkeys. They would not let me spray them with anything and their feet and legs were raw where the flies had been eating on them. Started feeding this and withing 3 weeks could tell a significant difference and hair is growing back on their lets.
Edna S on Aug 14, 2018
Great value for a great product
reginald m on Jul 28, 2018
I have never tried it before and my horses are miserable, fly spray doesn't seem to keep up so trying an internal solution.
Anne S on Jul 26, 2018
been using forever with great results
Judith M on Jul 18, 2018
Keeps flies from barn and pasture
Charlotte W on Jul 16, 2018
I heard this was an excellent product that worked well for removal and relief of flies. Have yet to try it but am looking forward to seeing if this product can help our big guy, as he gets eaten alive by the flying bugs.
Teresa B on Jul 11, 2018
This is the second year that I have used this product and it seems to be very effective around my barn. Although I still have a few flies, the number of flies is greatly reduced. There are cattle that border my fences which will add to the fly problem, however, this product seems to help greatly in my pastures. I also have chickens that free range and I see no problem using this product on my farm. The taste of the product is palatable to my horses, also. Great Product!
Teresa B on Jul 10, 2018
hoping to address the problem from both ends
Dedie S on Jul 9, 2018
Works as advertised !!! Keeps the flies at a minimum.
Cindy J on Jul 8, 2018
it works
crea b on Jun 30, 2018
Works well to help reduce flies
Pamela P on Jun 26, 2018
I have used this for years and it works, we use it year round due to our warm weather
Cindy L on Jun 26, 2018
It's been effective in keeping the flies at bay. I started late this year and they still aren't nearly as bad as I'd expected.
Angela M on Jun 25, 2018
I have a horse who always attracts flies but for some reason, this helped stop it.
Stephanie R on Jun 24, 2018
it works and was on sale
belinda p on Jun 24, 2018
Used successfully before.
Ronald K on Jun 23, 2018
I've been using Simplifly for several years and see a noticeable difference in the fly population.
Linda E on Jun 15, 2018
We recently moved our two horses to the house and we are starting to have fly problems on property. I need something that will help to keep the population from getting out of control.
Mary Beth P on Jun 13, 2018
greatly reduces fly population. Remember, only works if all horses on or adjacent to property get it.
Roseann B on May 29, 2018
Good reviews
Caroline L on May 29, 2018
so for i can see improvement in less flies
H Thomas B on May 25, 2018
I've been using SimpliFly for years. It really does hold down the fly population!
Mary T on May 21, 2018
It works!!! Keeps fly population down .
Cindy L on May 19, 2018
This is our go too product for flies
Patrick C on May 19, 2018
This product has REDUCED the amount of flies in our stables, not completely removed them but it is doing an 'okay' job.
Isaias A on May 8, 2018
I have horses and fight flies ever year. I'm hoping this will help with the problem.
Daniel G on May 7, 2018
We have used SimpliFly for years at our barn. It is great. I never realize that we don't have many flies until I go to another barn.
Laura W on May 7, 2018
I don't like flies
Tammi T on May 2, 2018
Because it's fly season, and this stuff works!
LISA G on Apr 30, 2018
I have a fly problem
Stacey D on Apr 27, 2018
First try on this product. Have used other Farnam products with good results.
Linda C on Apr 27, 2018
Works great.
Audrey S on Jun 6, 2019
I chose this because it absolutely works! I've been feeding this to my gelding for the last 5 years now and am completely satisified with the results.
Tara S on Apr 28, 2019
Can you feed this to a pregnant and nursing mare?
Brandi S on Jun 23, 2016
BEST ANSWER: Yes, it simply goes all the way thru without metabolizing , just makes the manure unfriendly to fly larva, so doesn’t affect the pregnancy or the milk. That’s per the label, I fed to several pregnant mares, and babies and mares are fine, this is the fourth year I’m using it
My dogs love to eat horse poop. Will will the Symplifly harm them?
Susan C on May 7, 2017
BEST ANSWER: I have been told by my dogs vet that they would have to eat quite a bit of the raw product in order for it to cause an issue. Even tho my dogs have never shown an interest in the container, I make sure to latch my feed room door when I'm not at the barn
I have 5 miniature horses.How many of my horses will I be able to feed for a month with 10 pounds of this product?
Charlie P on Jan 15, 2014
BEST ANSWER: Charlie, miniature horses should be fed 2/5 ounce once a day (I have Arabians).....not sure how many ounces are in 10 pounds of SimpliFly (I purchase the product in much larger amounts) but it should be listed on the container. Divide .40 into the total ounces, then divide that by 5 (number of horses) and you'll have the number you need. As an aside, it works great....I've used it for the past several years, along with a spray that's dispensed with an automatic sprayer (mainly for the mosquitoes) and am virtually fly and mosquito free.
How much of it do you give each horse? I am using it on donkeys. 1-2 Tbs?
A shopper on Apr 26, 2017
BEST ANSWER: Daily Dosage:
300-500 lb. horse, pony or miniature horse: Feed 2/5 oz. per horse per day (one measuring cup filled to the blue line)
500-700 lb. horse or pony: Feed 3/5 oz. per horse per day (one measuring cup filled to the red line)
700-900 lb. horse: Feed 4/5 oz. per horse per day (one measuring cup filled to the green line)
900-1100 lb. horse: Feed 1 oz. per horse per day (one full measuring cup)
1100-1300 lb. horse: Feed 1 1/5 oz. per horse per day (one full measuring cup plus one measuring cup filled to the black line)
For larger horses over 1,300 lb. of body weight or draft horses, feed an additional 1/5 oz. for each additional 200 lb. of body weight.
Is there ANY toxicity for horses from this product? What are the negative side effects?
Connie S on Jan 28, 2015
BEST ANSWER: I've been using it for years and never had a side effect. (I did not use if with pregnant mares). A HUGE difference in the fly population while using it. Much better results that fly predators.
Is this safe for goats?
Christine B on Jun 2, 2018
BEST ANSWER: I bought it for my horse. Did not use it on my goats
Will this work if other horses in the same barn aren't on it?
A shopper on May 27, 2017
BEST ANSWER: There are 8 other horses in my barn who do not use this product. We all pick up our droppings once a day, put them in buckets and wait for the workers to pick up and spread in the field. I feel that my 2 who are using this product are helping keep down the population, but it is really hard to tell. I feel like there are less flies in my stalls but that could just be a perceived thing.
I have a picky eater.. does anyone else have a picky eater that had a problem finishing their food with this product in it or did they eat without issues?
Whitney V on Feb 11, 2017
BEST ANSWER: we also have a picky eater, adding this product does not seem to matter......he is still picky but no more so. I give it to him with grain, giving him only a half serving of grain at first with the Simplifly, feed the other animals, then back to him with remaining normal portion of grain, mixing it again with any Simplifly he did not eat initially, in hopes his initial hunger has caused him to eat most of not all of both grain and Simplifly. Works more often than not. He does not seem to care that the Simplifly is there or not, he just picks no matter what.
Has anyone ever purchased the large container and used leftover product the following year? I was just wondering if the product remained stable and effective.
Katie on Mar 2, 2014
BEST ANSWER: When we were in Oklahoma, I did carry it over to the next summer, and it seemed to be just as potent. Now that we are in Texas, we have very warm periods throughout the winter so the flies are not completely dormant. Therefore, I now use it year-round. It really does work!
Does it also work on the gnats?
Janet M on Jun 2, 2014
BEST ANSWER: Janet M: I really do not know if it breaks the growth cycle of gnats as it does for flies. Simplifly travels through the gut and exits in the manure. It is my understanding that flies will still lay eggs on the manure but that the hatchlings don't mature to make more flies.

I use FlyRid every other week on my horses to keep the flies, ticks, gnats, etc off them. It is amazing to watch a horse fly zoom in and take off again without ever landing -- gotta be the FlyRid working!

Hope this helps.
I board my horse will it help him if other horse's are not on this product?
A shopper on Mar 2, 2017
BEST ANSWER: While SimpliFly is the most effective feedthrough fly control I've used, I'm not sure of its effectiveness when pasture mates/barn mates are not using it. Keep in mind there will still be flies where you're boarding, as you'd only be treating your horse. Maybe you can get the other boarders to share in the cost of buying the 50lb tub!
Does this work for Ceratopogonidae, aka no see-ums or biting midges? They breed in waterways,not manure. My horse has severe allergies.
L.K. M on Jan 11, 2019
BEST ANSWER: Nope, the only thing we've found that helps with the biting midges is spraying the horses. We put a granulated pesticide down in the pasture near the house and spray the yard and house with a pesticide and that helps with no-seeums mostly, but not the biting midges. My wife mixes an all natural bug repellent for our colts, but the only ingredient I can remember is peppermint oil. Maybe you can google if you need something like that. As for the Simplifly, it works great if you'll start a week or so before the flies come out and then use it til they're gone (that's about 9 months here). Cut the number of flies probably in half the first year we used it, and after a few years consistently using it & fly traps we have very few flies now. Last year we started Simplifly in March and put out fly traps and didn't fill those traps. The first year we did both we were changing the fly traps at least every week.
What size dose is the # of days supply based on?
Susan on Sep 21, 2018
BEST ANSWER: I have never actually out it on the calendar to see how many days I get, but I give a full scoop (that comes in the tub) each day. I think the directions call for one scoop = one dose.

I can tell you, I really believe this product cuts down on the fly population. I have been using it year round for almost 20 years. I scoop up the poop frequently and in the warmer months I can see a swarm of little flies come up from the poop -- those flies won't mature because their exo-skeletons can't grow (that's how the product works). It is safe for other pets that might eat horse poop (yes, I had a dog that did and I called Farnam -- it's safe).
Does this work against Horse Flies too?
A shopper on May 9, 2018
BEST ANSWER: I have been using this for years and was never really sure just how effective it was until we moved our herd of 12 horses out to our family farm. Even before we had any livestock out there the horseflies would swarm our vehicles as we drove in through the gate. 2017 was our horses first summer there and the horse fly problem has gone! Even our neighbors have commented on how it is safe to be outside in the summer. I’ve recently read that horse flies lay their eggs in water rather than manure, but maybe they lay eggs in the puddles around the manure pile. All I know is the thousands of horse flies that plagued us humans have simply disappeared.
Would this work for dogs the flies are bad? I have tried everything
Heather F on Aug 14, 2016
BEST ANSWER: Heather I'm not sure it would be effective (& might be unsafe) if used in a dog. I looked on the bucket & there wasn't a warning about it. There is a product info # you can call. This site won't let me include the phone number so try googling Farnham Product info. Sorry.
are there concerns if a horse were to eat the entire 5gal bucket?
A shopper on May 23, 2016
BEST ANSWER: I would be concerned if a horse ate 5lbs at one time. It is a pesticide, and while technically it is a "feed through" and supposedly not absorbed I would worry about large amounts being ingested. If you have an issue with an insecure feed room and it is a real concern maybe keep the large bucket elsewhere (at home? in tack room?). I premeasure mine into ziplock bags mixed with the senior feed, so if my horse WERE to get into it it would be diluted already.
It is only a simple alfalfa base, rather than tasty grain/molasses base, so anything else in the area is likely to be more appealing to a loose horse or mice.
how many green cups in a 50 pound container?
jerry t on Apr 7, 2014
BEST ANSWER: Each of the small cups that are contained in the bucket holds 1 oz. That is the correct dosage for a 900-1000 lb horse. I buy the 20 lb container and it lasts me about 5 months for my two 1000 lb horses.

In a 20 lb container there should be about 320 of the small cups. In a 50 lb container there should be about 800.

There are graduation lines on the cup to adjust the dosage for smaller or larger horses.

I find this to be very effective in reducing the fly population in my barn.
Does it harm chickens who eat horse manure?
Alice L on Jul 1, 2019
BEST ANSWER: Doubtful, but you can call the manufacturer to verify. They are helpful. I had a horse get into it and ate 3 pounds. I called vet and manufacturer..nothing to worry about with overdosing, so pretty safe all around.
Can you give it to pregnant nursing mares?
Nina B on Jun 15, 2018
BEST ANSWER: Yes, Simplify is safe for pregnant mares. The active ingredient is not absorbed. It's passed unchanged in the manure where it prevents flies from breeding.
Is this safe for cats?
Donna B on May 20, 2018
BEST ANSWER: I don't know about cats. We had a small dog that loved to eat horse poop. I was concerned about the SimpliFly in the poop being harmful. I called the Farnam headquarters (phone number was listed on the label back in 2003) and was assured that our dog was safe. My advice to you is to call and ask about the safety for cats as their digestive systems seem to be different from those of dogs.
what is the shelf life of simplifly?
A shopper on Apr 30, 2018
BEST ANSWER: I don't know the exact shelf life but I do know that I buy it by the 50 lb tub and it lasts our three horses for several months. Also, our farrier does comment on how few flys we have compared to other farms he visits. We've been using it for about two years with noted results.
Will this product harm dogs that eat the product that the horses drop on the ground as they eat it?
A shopper on Apr 3, 2018
BEST ANSWER: I would suggest that you ask this question to Farnam. This is the best product I've used to maintain the fly population, but I'm not sure how to answer this question. SImpliFly is mixed with my horses grain and they're fed this in their stalls, so my dogs don't have the opportunity to eat it. Good luck with finding a response to your question!
If my dogs eat the droppings from the horses with this fly control product in it, will it hurt the dogs?
Ann M on Feb 22, 2018
BEST ANSWER: No, SimpliFly is safe for dogs and wildlife. My dogs have munched on horse manure with no ill effects except for bad breath. This is a very effective product.
Does anyone know of a product i could use for ticks?
Chantle S on May 1, 2017
BEST ANSWER: Simplifly is a feed-through product that prevents fly babies from growing and making more flies. I use it in TX year-round. Depending on where you are and the how long your deep-freezes last, you might be able to stop during the bitter freezing weather months. In Dallas area, Texas, we might get only a few days.

But Simplifly won't do anything for ticks. I use Fly-Rid, a top-spot product (like you might put on your dog or cat), to control flies (many varieties) and ticks from attaching/biting my horses. It is quite amazing to watch a horsefly zoom in, hover about one inch above the rump and then take off again. Fly-Rid is the only product I use for that purpose, and I've tried them all!
Does this is good to feed cows ?to keep them free of flies thus cows are been milked everyday please pay attention to it!
La chula on Mar 21, 2017
BEST ANSWER: Probably not. This product is formulated for use with horses, and specifically cautions not to use on horses intended for slaughter. Please also check with your cows' veterinarian.
Is this product safe for donkeys?
David S on Mar 10, 2017
BEST ANSWER: I don't know for sure, but it most likely is. I'd recommend checking with your vet. :-)
Can i give this to shetland ponies?
Sarah C on Oct 22, 2016
BEST ANSWER: Yes you can they have different measurements on the scoop for pounds per horse.
We give it to our miniature donkeys.
They get up to the black line on the scoop!
Is is safe to use horse manure for gardening that has Simplify in it?
A shopper on Oct 24, 2015
BEST ANSWER: When I checked the Simplifly website, it said not to feed pregnant mares Simplifly. It was okay for everything else. I wouldn't think it would harm garden, as it only keeps flies exoskeleton from hardening. I also contacted the website to find out if it would harm the fly predators that I put out. They said it would not affect the fly predators. Check their website and ask them the question, if it still concerns you.