As the fly season begins, the Iowa Beef Center offers tips for how producers can minimize the stress and health problems flies can cause your cattle. Ken Holscher, associate professor in the Entomology Department at Iowa State University and cooperator with the Iowa Beef Center, says producers have several options available for fly control. "Fly control measures depend on two criteria: Whether the producer has pasture or feedlot animals and what types of facilities and equipment are available. All fly control options have limitations, so producers need to evaluate their secific needs and choose wisely."

Pasture Control – Chemical
Horn flies and face flies are the two main species that affect pastured cattle. Although the most effective means of controlling them are primarily chemical, there is a variety of application methods. Equipment and facilities will dictate which measures are best.

  • Sprays. "Fly sprays are effective and fairly inexpensive," Dr. Holscher says. "However, the effectiveness wears off after about 30 days, so the cows must be treated once a month throughout the fly season. Then the question becomes can and do producers want to continue treatments?" Dr. Holscher adds that treating cattle during the hottest parts of the summer may cause stress.
  • Pour-Ons, Spot-Ons and Squirt-Ons. Pour-ons are ladled across a cow's back, spot-ons are applied to one spot on the cow's back and squirt-ons are applied to the backs of cattle using a squirt gun mechanism. All three are equally effective, however, they still must be applied once per month.
  • Forced-Use. Forced-use methods include back rubbers and dust bags and are relatively inexpensive and effective. "Using self treatment takes a little more preplanning by the producer," Dr. Holscher points out. "Cattle have to use these daily for them to work, so placing them directly in front of food or water is the best bet."
  • Feed Additives. Feed additives control fly larvae developing in cattle manure. "This approach takes a lot more management than the others," Dr. Holscher says. "The cattle must ingest the right amount daily - not too much and not too little. Obviously, cattle don't know a whole lot about their rations, so producers need to be proactive when using this method."
  • Ear Tags. Even though there is speculation about resistance to ear tags, Dr. Holscher says they are still a viable option for many producers. "For ear tags to work, producers absolutely cannot use pyrethroid tags for more than one year. They should alternate with organophosphate tags every other year," he says.

Pasture Control – Nonchemical

  • Bruce Fly Trap. The Bruce Fly Trap became popular in the 1920s and 1930s and is experiencing a rebirth of sorts. Named for its inventor, the fly trap is usually built from wood or polyvinyl chloride pipe and fine screens. When the animal walks through the framework, the screens scrape the horn flies off. It has no effect on face flies, and cattle must be forced to use the fly trap every day.
  • Mechanical Controls. "Flies lay their eggs in fresh, undisturbed manure. The manure must remain intact for the larvae to hatch," Dr. Holscher explains. "Harrowing pastures regularly would break up the manure and kill the eggs and larvae."

Feedlot Control
Stable and house flies are the main pests found in beef feedlots. House flies are usually only a nuisance, but stable flies feed on blood and attack the animals' legs and ankles with painful bites.

"The best method of controlling flies in feedlots is sanitation and manure management," Dr. Holscher says. "Flies need manure and other materials for laying their eggs. By trampling and scraping manure, eliminating standing water and cleaning up spilled feed and silage, much of the fly problem can be eradicated."

There are several products available to supplement sanitation practices. Residual wall sprays last three to four weeks and are applied to areas where flies rest. Knock-down sprays supply a quick but temporary removal of flies from lots - they must be used daily. Feed additives can be an option, however the active ingredients are deposited in manure, thus, they won't control flies developing in other breeding materials.

"Some producers have tried parasitic wasps in their feedlots," Dr. Holscher says. "These wasps attack and destroy flies. They've been useful in poultry confinement buildings, however, their use in feedlots is somewhat limited. Studies are underway to determine why they don't work as well in feedlots. Using this method requires a lot of management, because a person needs to know where,
when, how many and how often to release the wasps. It's probably not the most feasible choice for feedlots."

None of the techniques listed have changed much over the past 20 years. "There's really nothing new on the horizon as far as fly control," Dr. Holscher notes. "But the current technology is effective; we have to make good use of what we already have."