If you could add more than ½ lb. of gain/day for lots less than it costs, chances are you’d do it. That’s the worth of fly control.

A few years back, University of Tennessee researchers compared a group of backgrounding calves with flytags to those without. The tagged calves gained 2.34 lbs./day, compared to 1.90 lbs. for the control group; 88 lbs./head more across 120 days.

Likewise, Jane Parish and Blair McKinley, Mississippi State University (MSU) Extension beef specialists, estimated in 2006 that flies can reduce stocker gains from 30-70 lbs. during a summer stockering season.

Various estimates peg the cost of flies to the U.S. cattle industry at upwards of $2 billion annually; more than $1 billion/year for horn flies alone. Even so, the MSU specialists went on to explain that stocker producers often ignore fly control.

John Maas, University of California-Davis Extension beef cattle veterinarian, says too many producers rely on just one chemistry or kind of application, which reduces overall effectiveness and can build resistance in the flies.

Depending on where you run cattle, face flies or horn flies are often the primary culprits. Face flies feed around the eyes of cattle, causing irritation and transmitting the bacteria that causes pinkeye. Horn flies are blood-sucking critters, each one feeding up to 38 times/day.

“Sprays, back rubbers, face rubbers, pour-ons and dust bags can be helpful in reducing the fly populations early in the season, before ear tag application,” Maas says. “Then, as the fly populations increase, apply fresh eartags to achieve maximum benefit.” He explains waiting to apply tags until later in the season when fly populations are denser helps decrease seasonal resistance.

“For maximum prevention, it’s advisable to switch the class of insecticide you use each year or two. If you used an organophosphate ear tag last year, use a pyrethroid ear tag this year,” Maas says. “Additionally, if you plan to use a pyrethroid eartag this year, use an organophosphate spray this year. Alternating the classes of insecticides in this manner will increase the success of your preventive program.”

For the last 20 years, the choice for insecticide tags has revolved around those containing organophosphate, pyrethroid or previously used insecticide chemistries offered as a tag application. This spring, tags containing a new compound – abamectin – became available.

“This gives us a third chemistry to use in rotation and should help minimize the impact of horn fly resistance,” says Joe Kellerby, vice president of specialty products for Y-Tex Corporation, which manufactures the new tag (XP 820™). Kellerby explains EPA approval of the tag marks the first animal use of abamectin in the U.S.; it’s part of a different family of compounds called macrocyclic lactones.

“In areas where you have resistance building, this chemistry will be more effective,” Kellerby says. “In areas where resistance isn’t a problem, it’s as effective as the other compounds available.”

According to the MSU specialists, some things to keep in mind, depending on the chosen fly control application:

  • Sprays provide quick results and may provide some control for 2-4 weeks, depending on rain which washes off the chemical. Several applications during the fly season are necessary for desired results. Sprays work best when used in combination with other control methods.
  • Pour-ons applied down the backline provide control as an initial treatment but are only effective against blood-feeding flies and for only a few weeks.
  • Rubs treated with an insecticide in an oil base can be used as a stand-alone control measure. The rubs must be recharged every 2-4 weeks or following significant rainfall. Rubs are most effective if placed in gates or around mineral feeders where cattle are forced to use them.
  • Dust bags containing insecticide are similar in effectiveness to rubs if cattle are forced to use them. The powder in dust bags may become caked under conditions of high humidity.
  • Fly-control ear tags are one of the most popular means of fly control because of their convenience. Tags are to be applied in late spring or early summer after flies appear and should be taken out when they become ineffective or at the end of fly season. Fly tags are most effective when the insecticide chemical class is alternated from year to year. To reduce the chance of flies developing resistance to various chemicals in eartags, it’s a good idea to spray at least once during fly season. Leaving fly tags in year-round can lead to increased resistance to insecticides in the fly population.
  • Oral larvicides are compounds fed to cattle via their ration or in mineral to kill fly larvae as they hatch in the manure. These compounds are only effective when animals consume the proper amount of the active ingredient. Oral larvicides don’t control migrating adult flies. Adult flies can still be a problem if a producer is using an oral larvicide, but a neighbor is not practicing any fly control.
More detail is available in “Stocker Growth Expectations”.