No fly zone: Managing for flies may require a combination of chemical, biological and physical methods |

No fly zone: Managing for flies may require a combination of chemical, biological and physical methods

THE PROBLEM OF RESISTANT FLIES - Nancy Hinkle, PhD, Professor of Veterinary Entomology, University of Georgia says that unfortunately the cattle industry has become very dependent on insecticides and now we are faced with new generations of flies that have become resistant to these weapons.

“Chemical companies can’t spend as much money developing new pesticides for the cattle market as they can for corn or other crops with huge acreages where they will be able to sell millions of dollars’ worth of products. The cattle industry is at least a generation behind the crop farmers. The farm market has also developed alternatives such as biological control,” she says.

“We need some new methodology for cattle, especially to control horn flies, since they are still the number one pest bothering our cattle.” Any chemical control program for horn flies must alternate/rotate different chemical classes as the flies become resistant to whatever is being used.

BREEDING RESISTANT CATTLE - A few people are developing lines of cattle that are less attractive to horn flies; there are some breeds and some individuals within breeds that are resistant to flies. With selective breeding a person can utilize those genetically resistant animals and select for that trait along with the other desirable traits we want in our cattle. Most producers are more interested in other traits, however, in their selection process. Fly resistance may be low on their list of priorities.

“It takes a lot longer to produce a line of cattle than to produce a new soybean!” says Hinkle. “It is doable, but something a person has to commit to. Today, with more knowledge of genetics, and genetic engineering, we can probably cut down the time it would actually take to produce more fly-resistant cattle,” says Hinkle.

Flies are a continual problem during warm weather, but there are several ways to reduce these pests. Different flies have different habits and behaviors, so a combination of tactics is most effective if you are trying to reduce several types of flies. Houseflies and stable flies breed in rotting organic matter such as old hay, silage and other feeds, and bedding. Horn flies breed in fresh cattle manure but spend all their adult life on cattle. Horseflies and deerflies breed in swampy areas, and black flies breed in flowing water — often many miles away — so it’s impossible to control them at their breeding sites. Cattle producers need many different weapons and options for fly control.


Stable flies can be controlled effectively by cleaning up old organic debris that serves as breeding sites, like wasted hay around big bale feeders, old bedding, etc. About 95 percent of the stable flies develop in less than 5 percent of the area where cattle are located. If you can clean up those areas, you can make a big difference. A Texas research project found more than a million stable flies in the debris from each round bale site (that didn’t get cleaned up off the pasture in the spring). Residual debris from wasted feed, or even a heap of leaves along the edge of a creek or ditch that washes them up into a pile, can create breeding ground for stable flies. If producers can clean up rotting material before fly season starts, spreading out the piles so they can dry out, or piling them in a correctly built compost area, this debris won’t be propagating flies. Black plastic over the top of those big compost piles can bake the maggots.


These tactics include use of other insects or animals to feed on the fly eggs, larvae or adults.

• Parasitic wasps: These tiny wasps lay their eggs in fly pupae in manure and debris, and the developing wasp eats the fly pupae before they hatch into flies. These wasps can be ordered from mail order farm supply catalogs or directly from Spalding Laboratories (5,000 for $19.95, 10,000 for $29.95, 20,000 wasps for $51.95). The key is to start using them early in the season before the fly population grows large, sprinkling them in manure areas around the barnyard and adding additional wasps every 4 weeks. These can help control manure-breeding flies in a small area like a barnyard or feedlot but won’t work in a large area like a big pasture.

• Dung beetles: These beetles reduce horn fly numbers dramatically by disrupting the manure pat. There are several species of dung beetle native to North America and some that have been imported and released, but there are none commercially available. These insects spend their lives in manure. Adults use liquid components as nourishment and lay eggs in the manure pat. Hatching larvae consume manure. Some species remove and bury balls of manure containing their eggs. An active population of dung beetles can bury or destroy 95 percent of horn fly eggs and larvae and about 90 percent of other cattle parasites that are passed in or depend on manure. Even if fly eggs hatch, they can’t get back up to ground surface after dung beetles bury the manure. Birds are attracted to manure containing dung beetles, and tear the pats apart to eat them—which helps spread manure and disrupt fly larvae development. A single manure pat without dung beetles can generate 60 to 80 adult horn flies.

The best way to have lots of dung beetles is go easy on chemicals. Avermectin dewormers and pesticides destroy dung beetles. Long-term control of flies is often better achieved by dung beetles (to degrade the manure) than by sporadic application of pesticides.

• Chickens or ducks: Some stockmen with small herds augment their control of flies with free-range chickens. Pastured chickens used in conjunction with intensive rotational grazing, following the cattle, scratch through manure pats to eat the “bugs” and basically destroy these breeding sites for horn flies.

The same benefit can be obtained using Muscovy ducks. This breed is not a water duck; it eats insects and doesn’t need commercial feed. The ducks range freely in pens and pastures and are prolific breeders. They follow cattle around, searching through manure and scattering the piles so thinly that no fly larvae survive. It takes about 4 ducks per cow to adequately control the fly population. The ducks also eat adult flies and pick flies off cattle when they are lying down chewing their cuds. Cattle become accustomed to the ducks and stretch their heads and necks lower to the ground (while lying there resting) so the ducks can reach more flies.


Most fly traps work best for horse flies and deer flies. There are also sticky traps for stable flies. Those flies take a blood meal and leave, whereas horn flies never leave the host animal. Traps for house flies don’t work on any of the biting flies because they are attraction baits; they don’t use the same food source.

The only trap that removes horn flies is a cow vacuum. It’s an enclosed area the cows walk through; it blows the flies off the animals and sucks them into a bag. The machines can cost up to $8,000 and are used mainly in dairies since they are more conducive to a confinement situation.

A commercial trap for biting flies (Epps Biting Fly Trap, sold by Horseline) has a dark-colored panel to simulate the silhouette of an animal, with light-colored panels above and below. Horse flies or deer flies tend to fly over and around an animal before biting; they strike the light-colored panels and fall into soapy water in trays under the trap. Soap breaks the surface tension of the water so they can’t float—and drown. This trap works well for horse flies and deer flies but not horn flies.


There are many kinds of sprays, pour-ons, injectables, etc. for killing flies. Here are some of the main ones used by cattlemen:

• Dust bags and oilers: Traditional back rubbers, oilers and dust bags are helpful in situations where cattle have to go through a gate, or learn how to use them in a small area. Cattle enjoy rubbing on these because it gives them some relief from horn flies, but you still have to go out there and recharge the dust bag, oiler or back rubber.

One type of rub (cost—about $30) is a ten foot, large diameter synthetic material that will not rot. A strong polypropylene rope (break strength 2,700 pounds) runs through the center and out each end for hanging (attaching to gate posts or some other structure or between two trees). The rub rope can be charged with 4 gallons of insecticide/diesel fuel mix along its entire length and cattle self-applicate when rubbing their backs on the rope.

There are many types of dust bags on the market including Y-Tex, Durvet, ProZap dust bag kits ($30 to $60). The dusts and liquid products (for oilers/rubbers) work well, as long as the flies have not developed resistance to these chemicals, and the applicators stay full.

• Pour-on products: There are numerous types of pour-ons containing various chemicals including pyrethroids, permethrins, and the newer avermectins (such as Ivomec which is $39.95 for a 250 ml bottle) that target both internal and external parasites. Some of these are affective against horn flies for several weeks.

• Insecticide ear tags: These are probably the most popular control method because ranchers can install the tags in early summer and hope for control of horn flies and face flies through most of the fly season. There are numerous trade names/brands currently marketed, containing pyrethroid, organophospate, and avermectin insecticides. Depending on the product, one or two tags are installed per animal. Horn flies in some regions and on some farms have developed resistance to pyrethroids. Organophosphate tags will control pyrethroid-resistant horn flies. Ear tags release insecticide most efficiently during the first two months after application.

One new ear tag (Tolfenpro, by Bayer) came out last year, using tolfenpyrad as the insecticide. Researchers at University of Georgia received some of these tags in late 2015 to test, and were impressed with it because it kept fly numbers down below 50 per head, for a full two months. The control animals had 200 to 300 flies per animal.

These new tags are not like pyrethroid tags; they don’t completely wipe out the flies, but do suppress them. Flies will eventually become resistant, however; anything that a producer uses consistently will lead to resistant flies. But this gives us one more tool, for now.

• Feed-through products: There are several kinds of feed-through products that are added to feed or mineral mixes. They end up in manure and affect the species of flies that lay eggs in fresh cow manure. Some of these products contain a larvicide that kills the fly larvae, while other products contain insect growth regulators which affect the larvae, and they don’t mature to become flies.

• Injectable parasiticides: These are products containing ivermectin and related avermectins (macrocyclic lactones) that mainly target internal parasites but can also kill external parasites that feed on blood (such as horn flies). One of the newer products, LongRange, is injected subcutaneously and the protective effects last 100 to 150 days. Even though it is not labeled for flies, some stockmen are using for fly control as well as a dewormer.

• Space sprays: These are concentrated products that you add to several gallons of water, for spraying around a barnyard or in a barn. An example is Pyrahha fly space spray (2.5 gallons – $204.95 – added to 55 gallons of water) for use in an automated barn spray system or small amounts added to a gallon or two of water for spot spraying around the premises. It provides quick knockdown and long-lasting control of most biting flies and mosquitoes.

• Vet Gun: This is a new method for applying insecticide to cattle. It works like a paint gun, shooting a ping-pong size ball of insecticide, enabling the producer to “shoot” the product onto the cattle from a safe distance away. It can be deployed from an atv, vehicle or horseback. The gun doesn’t make as much noise as a real gun but sounds similar to a BB gun. The insecticide it “shoots” is not a new chemical. It is lambda cyhalothrin, the same as the active ingredient in Saber pour-on. This is a pyrethroid, so if flies on a certain premise have already become resistant to pyrethroids it won’t be very effective. F

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