June 2006
From the State Vet's Office

Fly Control Will Pay for Its Investment

Fly Control Will Pay for Its Investment

With the blooming of flowers, warm weather and green grass comes a pest that is very costly to the cattle industry. External parasites such as flies and mosquitoes cost the cattle industry billions of dollars each year in lost performance.

Flies can reduce weaning weights in calves by as much as 5% when compared to calves on farms that have an external parasite control program in place. Also, flies can reduce brood cow weight, reduce grazing time, reduce milk production and be the cause of/or help spread disease such as mastitis and pinkeye.

There are several products available to use as a control for flies. While sprays, back rubbers, and fly tags are all available and will assist in your management program, I would like to discuss two options available in a mineral program as a means of effective fly control. These products are available in mineral supplements and blocks with larvicides and insect growth regulators. Let’s look at each product and its mode of action to assist you in making a good decision for fly control this summer.

A larvicide (such as Rabon), as the name implies, affects the fly larvae in the manure of cattle and horses. When fed this product, it passes through the digestive system into the animal’s manure where it kills fly larvae on contact shortly after fly eggs hatch. This product is not effective against existing adult flies and should be fed early in the spring and continue to be fed throughout the summer and into the fall until cold weather restricts fly activity. It has been shown to be effective in the prevention of horn flies, face flies, houseflies, and stable flies. When used in conjunction with other management practices, it will assist in achieving optimum fly control. This product is available in both a loose mineral and a mineral block and can be purchased at special pricing through your local Co-op. It is safe for all stages of cattle and horse production.

Another product available to you is an insect growth regulator (IGR), such as S-methoprene. An insect growth regulator affects the development of the fly itself, which will lead to sterile flies that cannot reproduce. This product is to be fed continuously during the fly season to prevent the breeding of horn flies only in the manure of treated cattle. It is also available in a loose mineral or supplement block and is completely safe to feed to all classes of cattle. As with a larvacide, it may take from three to five weeks for an effect on the adult horn fly population to be observed. An IGR also has no effect on adult horn flies.

I visited with several farms that utilize one of these two methods as a fly control program. While not 100% effective, producers comment that both products work well as a control program and it is up to the individual producer to decide the product that will work best for their operation. Also, remember that the most effective results come from a program that has implemented other manage-ment practices as well as providing these products on a consistent free choice basis.

We have both a larvacide and insect growth regulator available to you at your local Co-op. We also have a wide range of other products available to assist you in a total management program. While these products will add initial cost to your program, the additional weight gain, disease reduction, and added performance will more than pay for your initial investment, plus you can ride around the pasture with the window down without fear of being overrun by flies.

If I can help you in any way, please feel free to contact me at This email address is being protected from spambots. You need JavaScript enabled to view it..

Jimmy Hughes is AFC’s animal nutritionist.