Integrated control strategies and new chemistry can help battle flies and their resistance.
No one's sure what Hell looks like, but it's a safe bet flies are buzzing around.
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.
Various estimates peg the cost of flies to the U.S. cattle industry at upwards of $2 billion annually; more than $1 billion each year for horn flies alone.
A recent study conducted by Iowa State University estimates the value of using fly control at $18/head in the cow-calf pasture, $7/head for stocker cattle.
Exploit the full arsenal
According to John Maas, University of California-Davis Extension veterinarian, most producers utilize fly control, but too many use only one type, which decreases the effectiveness of the method used and allows flies to build resistance quicker.
Maas points out 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. “Then, as the fly populations increase, apply fresh ear tags to achieve maximum benefit,” Maas says. 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 ear tag this year, use an organophosphate spray next year. Alternating the classes of insecticides in this manner will increase the success of your preventive program.”
For the past 20 years, the choice for insecticide tags has revolved around those containing organophosphate, pyrethroid and previously used chemicals offered as a tag application. Tags containing a new compound — abamectin — are now 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.”
“We need all of the tools we can get. It's always been a race to outrun tag resistance,” Maas says. As such, he advises using the newest chemistry available to begin a new rotation.
Moreover, Maas emphasizes effective use of fly-control products requires following the label directions. “If the label says two tags are required, use two tags,” Maas says. If you're using tags to prevent pinkeye in calves, Maas says make sure you tag the calves and not just the cows.
For those using pinkeye vaccines, Maas emphasizes that building protective immunity requires two doses and 45-60 days, so effectiveness demands vaccinating ahead of the season.
Finally, Maas says one of the leading contributors to resistance is leaving tags in the cows, rather than removing them at the end of fly season.