Successful Horn Fly Control Using IGR


Horn flies are one of the most economically important pests of domestic cattle and cause billions of dollars of damage and loss to the cattle industry each year.

Horn flies are small (3/16 inch long), dark gray flies that feed on cattle and occasionally horses.  Both sexes are blood feeders, taking 20 or more blood meals each day with their stiff needle-like mouthparts.  Irritations from the bites annoy animals and occasionally, the wounds may become infected.

Studies have shown that horn flies have their greatest effect on growing animals. They can be involved in causing “blind quarters” and reducing milk intake by beef calves because horn flies may carry S. aureus, a major cause of mastitis. The irritation and reduced milk intake from horn fly infestation can cause 20-25 pounds lower weaning weights as compared to cows treated with Altosid® IGR Feed-Thru. With calf prices at $300/cwt. the lost weight can dramatically decrease the income of cow/calf producers.

The key to a successful horn fly control program is starting early. It is important to start implementing your horn fly control program before you see an adult emergence. Below are answers to some common questions about horn flies and horn fly control using Altosid® IGR Feed-Thru.

Q: How can I tell if I have a horn fly problem?
A. Horn flies are an ectoparasite of cattle and tend to stay on the backs and sides of animals throughout the day. Despite their name, horn flies do not congregate on the horn and head area. Horn flies are about half the size of the common housefly and lay eggs exclusively in fresh manure.

Q: What’s the best way to control horn flies?
A. Most horn fly control strategies require you to either gather cattle on a regular basis for treatment or replenish the various systems that dispense products for horn fly control (dust bags, backrubbers, etc.). While these methods are labor-intensive, an insect growth regulator (IGR) allows you to provide horn fly control right in your feed or minerals, letting cattle do the work.

Q: When should I begin using an IGR product and when will I see results?
A. It depends on where you live, but 30 days prior to the last frost is the standard recommendation. You can start later, but you will definitely need to incorporate a knock down spray to kill adults that will be present if you choose to start later in the fly season. To effectively break the horn fly life cycle, a feed-through program using Altosid® IGR Feed-Thru requires three to four weeks for significant reduction in adult horn fly numbers.

Q: I use the product but I still see a lot of flies, why?
A. What you may be seeing are fly species other than the horn fly. The horn fly will only lay its eggs in fresh manure patties. Other fly species such as the common house fly, face fly and stable fly will lay eggs in any damp, decaying material such as sewage, near stagnant water or in old silage. Another reason might be lack of (mineral) consumption. Don’t let your mineral feeders run out! It only takes a few days without Altosid® for the level in the manure to drop below effective levels.

Q. How does Altosid® IGR Feed-Thru work?
A. Horn flies lay eggs in manure. After the eggs hatch, larvae (maggots) must molt as they grow. During this insects produce biochemicals to aid in the growth process. As the final growth stage, the pupal stage, occurs, the IGR provides a jolt of extra biochemical that interrupts the growth process. As a result, adult flies never come out of the pupal stage.

Q. If I’m using Altosid® and my neighbor isn’t, will I still get fly control?
A. The horn fly will not migrate. The female only leaves the host animal to travel a very short distance to the fresh cow patty, lay her eggs, and immediately return to the animal. Therefore, there is little opportunity for your neighbor’s horn fly population to cross over to your herd. Obviously, if there is shared shade or water along the fence line, there will be some slight cross over, but not significant.

Q. Can I use an IGR with other horn fly control products?
A. Yes. A complete program should include face fly control, along with adulticide products, depending on the level of initial infestation.

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