Farnam SimpliFly with LarvaStop

Regularly: $25.99

promotional discount applied.  Cart total will reflect savings.


Sometimes, manufacturers require that products be advertised only at their suggested prices. When we choose to sell these items for less, we display the sale price only in the cart. To see the price, click Add to Cart.

3 3/4lb
Less than $0.33/DAY
(60 day supply)


In Stock. Usually Ships within 24 hours.

Less than $0.31/DAY
(160 day supply)


In Stock. Usually Ships within 24 hours.

Less than $0.29/DAY
(320 day supply)


In Stock. Usually Ships within 24 hours.

Less than $0.22/DAY
(800 day supply)


In Stock. Usually Ships within 24 hours.

Shipping weight = 4.15 lbs.


Product Summary:

Farnam® SimpliFly® With LarvaStop™
Feed-thru fly control

SimpliFly® with LarvaStop™ is a highly palatable feed additive to prevent the development of stable flies and house flies in the manure of treated horses. LarvaStop™ breaks the fly lifecycle by preventing the formation of fly larvae’s exoskeletons when they molt, resulting in their death. This product contains no organophosphates and can be used as part of an integrated pest management program. SimpliFly™ with LarvaStop™ is a reduced risk pesticide.


  • Prevents the development of stable flies and house flies in the manure of treated horses
  • 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:
It is a violation of Federal law to use this product in a manner inconsistent with its labeling.

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.

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
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

Start typing your question and we'll check if it was already asked and answered. Learn More
Browse 27 questions Browse 27 questions and 182 answers
Why did you choose this?
Horse.com Store
Saw an Ad on RFD TV and thought it was a product to try.
Trish N on Jun 25, 2018
First time trying will let you know but read reviews and thought give it a try...
SUSAN W on May 1, 2018
Saw an Ad on RFD TV and thought it was a product to try.
Trish N on Jun 25, 2018
Have used before, they have a good price at Horse dot com
PAULA R on May 8, 2018
First time trying will let you know but read reviews and thought give it a try...
SUSAN W on May 1, 2018
Really helps with the fly control!
MELISSA T on Apr 22, 2018
I read the reviews, I feel I needed to try it. I am hoping for the best the summer.
LINDA C on Mar 13, 2018
Fly problem
Wanda C on Sep 20, 2017
Use this and love it. Works great.
Vickie O on Jun 26, 2017
Intrigued by the idea of using less fly spray. Ours are pasture kept, so I will treat all in our pasture. Hoping it helps!
Holly M on Jun 21, 2017
Prevents flys
WILLIAM R on Jun 2, 2017
"Simpli" put, It works!
Scott S on May 26, 2017
Thought I would try it for my pasture ornaments.
JULEE D on May 26, 2017
Good way to combat flies. My 2nd tub of this for the season. 3 horses fed 2 times a day, now will go to once a day
KELLY S on May 19, 2017
Best stuff ever! Simplifly has drastically decreased the number of flies we see on our horses, and in the barn. I begin feeding it in April after I begin seeing a few flies, and continue through late September. It even helps control the huge horseflies that come around in summer. I would recommend it to anyone who is interested in fly control.
Leslie C on May 5, 2017
Last year I battled with swarms of flies at the barn, in the pastures, and even at my house. This year, I found Simplifly and started using it in late February and the results are 'simplifly' amazing! Virtually no flies anywhere!! Love this product, and the horses love it too! Highly recommend it!
Donna B on May 4, 2017
GREG G on May 3, 2017
Continue to utilize this product with great results.
KATHY C on Apr 18, 2017
Great product, I worked at an Equine vet office and recommended this to a lot of people. It helped cut down the fly population at least 50% (I don't have a true stat but it felt like there wasn't half the flies compared to years without this product). Now, it didn't get RID of the flies, but I choose this product because it helps cut them back.
Speckowind on Apr 4, 2017
I'm going to give this a try. Haven't had any luck with other fly control except for sprays.
Judy K on Mar 31, 2017
does a great job keeping the flys away .. notice a huge difference.
NAN P on Mar 27, 2017
To decrease flies. Price is affordable.
Joyce P on Mar 23, 2017
It works great at keeping the flies down which is always a great help.
Debbie B on Mar 11, 2017
PATTY B on Feb 13, 2017
great product
ROSE G on Jan 23, 2017
I have a pony who is very sensitive to bug bites. I have had her on this feedthrough control to help keep the bugs off of her.
Angie B on Sep 4, 2016
It seems to be working, I noticed less flies on their body's and on me as well when cleaning up the manure piles. I will keep buying!
Valerie S on Jun 26, 2016
been using it for years
WILLIAM G on Jun 24, 2016
It works!
MARGO M on May 29, 2016
I am currently using this product and I like it. I see no flies on their manure when I pick up in the field everyday.
Christie C on May 23, 2016
My folks use this for their horses and seem to have better control than we do with fly predators
WENDY M on May 4, 2016
Want to try a feed-through fly control - fingers crossed that it really works!
JACQUELINE P on Apr 26, 2016
It is working. I have less flies around the barn, than at my house!
JENNIFER Z on Apr 25, 2016
It works.
Lori K on Apr 20, 2016
We have tried fly predators, but this product really works. we have 3 horses and people remark that there are no flies when they come. Our horses are in the back yard so its especially important not to have flies get into the house
ROSLAND L S on Mar 31, 2016
Simplifly has been amazing in the reduction of flies. We are well pleased with the results!
SHIRLEY J on Oct 30, 2015
Work's great to have a jump on the fly's. That's why I use this product and the horses like it. I can not say enough good things about this product.
teresa on Sep 17, 2015
I've been using Simplifly for about 8 or 9 years now with great results. Not only does it help around the barn, but it helps greatly in reducing the fly population in the pastures!
K I on Aug 14, 2015
have no flies in barns due to this product have been using it for five yrs.Not a fly repellant but deterrent.
H L on Aug 10, 2015
We just feel that it helps w/the reduction of flies at our barn.
TAMMY M on Jul 19, 2015
It works Fantastic!!!!
Shalette D on Jun 26, 2015
I buy it every summer for fly control. It works really good and also kills the larvae. It is an awesome product.
PATRICIA G on Jun 24, 2015
Keeps fly population down, horses like the taste.
DEBORAH B on Jun 21, 2015
Good stuff
Bill O on Jun 16, 2015
CATHERINE G on Jun 12, 2015
We live in the country, surrounded by thousands of acres of fields, forests, swamps, wetlands, etc, and have had periods of time where flies can be a problem. This stuff works.
DEANNE M on Jun 12, 2015
used it last year. seems to work.
sam l on Jun 9, 2015
I think this product is the best for my horses.
CAROLE B on Apr 29, 2015
Because of the promotional 3.75 lb with purchase of 20 lbs.
Teri Li T on Apr 24, 2015
Used last year and it worked well...also like the option for the large quantity to avoid having to reorder.
CONNIE S on Apr 21, 2015
I have one horse, and live near water. The flies are horrible here. This will be my first foray into feed-through fly control program. I hope it works.
rocky mom on Apr 1, 2015
This seems to work better for me than fly predators.
S G on Mar 12, 2015
Have used before, they have a good price at Horse dot com
PAULA R on May 8, 2018
Really helps with the fly control!
MELISSA T on Apr 22, 2018
Is this safe for dogs that may eat the horse manure?
A shopper on Jul 3, 2014
BEST ANSWER: Your best bet would be to ask a small animal vet. The active ingredient is an insect growth regulator and as such is probably specific to insects and not harmful to birds or mammals. On the other hand, it does say to keep it out of reach of children, so one could surmise that it might not be 100% harmless. Ask your vet and also contact a poison control center to be be safe.
can manure from horses fed simplifly be used in the vegetable garden?
A shopper on Feb 3, 2016
BEST ANSWER: I don't know if there is a scientific basis for not using it in the garden, but I have for years and it does not appear to cause us any problems. No one has gotten sick, but of course their could be a long term issue, but I have been using it and Equitrol in my horses and on my garden for 15 plus years.
Will this work if you have four horses but only two are being fed simplifly?
A shopper on Apr 4, 2016
BEST ANSWER: I have used SimpliFly for the past couple of years and it has reduced the flies some 85% or more. I have always given it to all my horses and I am not sure it would work properly if you only fed it to part of the herd. It is my understanding that the way it works is that SimpliFly ends up in the manure, the flies lay their eggs in the manure, and the little flies are born without an exoskeleton. It would seem to me that all the manure put down by horses not fed SimpliFly would help produce flies. And you know how fast they multiply, right?
Personally, I wouldn't take the chance. I love not having the flies and I think the horses do too. I have told several of my horse friends about our success and they like it too. Also, start early and don't stop when you get that first cold snap. When it warms up a couple of weeks later you'll have more flies than you did all summer put together.
Can miniature horses use this product? If so, how many would I feed?
Denise A on Jul 23, 2015
BEST ANSWER: We use it daily for our 4 miniature horses. Usually use about a tablespoon each.
is unused Simplifly good f

or the next summer?
clarence n on Sep 6, 2015
BEST ANSWER: I purchased a 50 lb bucket and used it for two summers and it was still effective. In fact, I believe it was more effective the second year for some reason. I am planning on purchasing another 50 lb bucket this winter for the next two summers.
The "other ingredients" are not listed. Does it contain alfalfa or just have an alfalfa odor? I have two horses sensitive to alfalfa.
A shopper on Jun 14, 2016
BEST ANSWER: No alfalfa, I have a horse that is allergic to alfalfa and she does fine with this
We are loosely affiliated with Save the Horses in Lathemtown, GA. 16 horses/2 donkeys. Is this product worth buying? Will it harm seniors?
A shopper on Mar 6, 2018
BEST ANSWER: We have used this product for 7 or 8 years now and love it. It is definitely worth it. We have an 80 - 85 % reduction of flies throughout the season. We have had a 28 yr. old, 20 yr. old and 17 yr. old horse on it and noticed no difference whatsoever when we start them on it in the spring nor when we take them off.
The key is start early and don't stop when you get that cold snap in the fall. It'll warm up again and you'll wish you hadn't stopped.
Hope that helps.
About how long does it take to notice results? I want to test it out, and I don't want to give in too soon, but the flies are very picky up here so I don't want to waste my time on something that doesn't work for me. Thanks!
Alley P on May 13, 2017
BEST ANSWER: For best results it's good to start feeding it to your horse(s) in early spring, depending on the climate you live in. It's not a matter of whether the flies are "picky" or not. The way the product is designed it's fed to the horse and pooped out. The ingredients are already in the manure so when the flies go to lay their eggs in it, it kills the eggs. The product stops the cycle of flies, leading to a smaller fly population. I stand behing this product and feel it definitely helps cut the flies down. I always pair it with the use of Fly predators and have had great results. If you wait roo long to start using the product, it will be hard to catch up and see a noticeable difference in the amount of flies. At least that's what happened to me in SC. I would go through one whole container to evaluate how well the product works for you. So. I would give it a couple weeks to work
I would only be using it on my horse there are other horses next to him in a in and out stalls. Will this still work on my horse?. The flies are awful this year. I can't be going everyday to spray him and when I do it very costly THANKYOU. Cindy
Cindy p on Jun 24, 2016
BEST ANSWER: Before feeding this to my mare and gelding I was pulling ticks off of them every day. After a couple of weeks I am no longer finding ticks on them (I've been feeding this since early May). As far as the flies...they are DREADFUL this year and I am having to put a fly sheet on my tender-skinned boy because he comes in from pasture with welts all over his belly and sides. Honestly...I truly can't answer your question...I keep my loves at a self-care facility with other horses and the bugs are insane. Nothing seems to be working other than fly masks and fly sheets. I continue feeding this because I DO know it helps with ticks.
Product description says to feed with your horses grain ration. My horse doesn't get grain. Can I still use this product?
J H on Jul 9, 2017
BEST ANSWER: Absolutely, I toss a scoop over their hay. It is in a pellet form so make sure you are feeding out of a bucket or you will lose it on the ground.
What is the difference between Equitroll II and Simplify, both Farnam products? I don't know which one to purchase.
Karla M on Jun 5, 2015
BEST ANSWER: I've never used Equitrol, so I'm sorry I can't really say. I've always used Simplify. ...works great at my barn! My horses are stalled 1/2 the time, turned out 1/2 the time, so it even prevents flies out in the pasture! Good luck!
Is SimpliFly safe for Pregnant mares?
Roy on Aug 21, 2014
BEST ANSWER: Hi Loren - Sorry I can't answer your question. I'm sure the folks at Farnam would gladly help you out. I can tell you this stuff really works so if they give you the green light you'll be very pleased with the results. It's just amazing how few flies there are around my barn. I tried Fly Predators and this stuff is so much more effective.
what is shelf life?
Jeanne F on Sep 18, 2018
BEST ANSWER: I am not sure of the total shelf life, but I had a 1/2 a bucket left in September and kept it through the winter and started up again in April, over 6 months later and it worked just fine. I really like Simplifly, and I was a real skeptic for years. But 2 summers ago I gave it a shot and I felt like a boob for not using it sooner because it worked without a doubt. Definitely over 50% less flies, probably closer to around 70-75% less.
Does this product control deer flies?
Judy E on Jul 30, 2016
BEST ANSWER: Can't say it actually "controls" ANY flies. What it does is stop ANY fly from (successfully) laying eggs in the manure, which helps minimize the number of flies in the field. We still get flies (stable, horse, deer) and I still have to spray my horses for flies. But they DON'T come from the piles of manure all over the pasture. I know that my pasture has a lot less flies than either of my other neighbor's pastures and am sure this is why. Have used it for 3 years now.
Is this safe for donkeys as well?
Jen D on May 27, 2016
BEST ANSWER: Jen, I am not a veterinarian and I am not giving you advice of any kind, I am only conveying my observations. Donkeys are equines, SimpliFly does not harm equines. For further insights or in-depth analysis, it is always preferable to seek the counsel of a veterinarian. Always follow label directions.
what happens if 3 horses eat 3 lb smiplifly container?
A shopper on Jun 29, 2015
BEST ANSWER: You really need to ask your vet. Many insecticides are harmful only to insects and should not harm mammals, at least in recommended doses, but I have no idea what effect it would have on a horse that ate 40 times the recommended dose. You obviously need to keep your supplements and medications in a safer place.
safe for pregnant mares?
A shopper on Sep 1, 2014
BEST ANSWER: I only have geldings so I cannot answer your question. My suggestion is to contact Farnam by phone. I have contacted them on one of their products in the past and they were very helpful. Simplifly is a great product. I start in very early spring and continue just past the first hard freeze. It's well worth the expense.
What about mosquitoes and the large horse flies ?
Penny A on Apr 9, 2018
BEST ANSWER: I find Simplifly works great when fed consistently to ALL of the horses at a facility. It does not, as near as I can tell, have any effect on mosquitoes. I do not know about the large horse flies as we don.t seem to have them. Maybe it is working on them too.
can this be used with horses that cant have sugar?
Abigail T on Jul 19, 2014
BEST ANSWER: I don't have the SimpliFly in front of me, so I can't tell you if there is any added sugar in it. I suggest asking your vet if it would be a safe product for your horse.
My problem is with ticks!!! Will this product help?
JANE K on May 5, 2018
BEST ANSWER: this is a feed through product that effects the larva stage of flys, the theory is the flys lay eggs in the manure that is where the process starts, I do not know if that is the same life cycle as ticks and breeding area, I keep my grass short and that keeps the ticks population down also use Smart Out from Smart Pak spray
Dose for minis ?
A shopper on Mar 25, 2018
BEST ANSWER: 1scoop. But flies are painful to avoid. I also get strips for the barn and a few bags that i put in the paddick abd manur pile area. I still spray because the do nothing for the horse flies. There are options for that, but it’s all ive got to offer
Can i feed it to my calf?
A shopper on Aug 14, 2017
BEST ANSWER: This product is not labeled for beef or dairy. I would suggest that you talk to your local feed man or feed store about a product with clarifly in it. It is the bovine equivalent to simplifly.
How well does this work on pasture horses?
A shopper on May 14, 2018
BEST ANSWER: If there is not a lot of other surrounding properties with horses, I would say this product definitely helps reduce the fly population. It's also highly palatable; I have a very picky eater and my mare ate it no problem mixed into her feed
Can this be fed to foals?
Sandra C on Aug 13, 2018
BEST ANSWER: If foal is in weight range listed below:
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).
Can any of these feed through products be used with pot belly pigs?
Bonnie on Apr 1, 2018
BEST ANSWER: This product is rated for use with horses only. We have to recommend that you check with your veterinarian before use on a different species.
After this season of flies, I would like to try this product next spring. My question is, my dog loves to eat their poop, will this be harmful to her?
Marie G on Sep 2, 2016
BEST ANSWER: I would consult with your Veterinarian