Emptying leftover water into calf pens is a huge mistake that flies will quickly use to their advantage.

When extension entomologist Phil Kaufman was called in to a 500-cow New York dairy, the fly problem was so bad that the calves had patches of hair missing from their legs because of bites from stable flies. Subsequently, a 20-foot sticky tape trap captured 10,480 stable flies and 5,507 house flies in the calf barn during early September.

The producer employed a pest-control service to spray for flies as his one line of defense. Since the company had a “no-flies guarantee,” it was visiting the farm quite often, but the flies were still winning the battle — especially in the greenhouse calf barn.

Upon further investigation, Kaufman found the calf-care employees were emptying leftover calf water into the straw-bedded pens instead of taking it outside. Adding water to the straw turned the calf barn into a fly resort. Eliminating that one practice brought about quick improvement.

“Sanitation and management are the two keys to successful fly control,” says Kaufman, with Cornell University’s veterinary entomology program. Without them, you can’t spray enough to keep flies under control.  Here’s why you shouldn’t rely on sprays as your first line of defense.

Seeing is not believing
Many producers believe that if they use sprays, they will get better control because they can “see” it getting done. But the truth of the matter is that “chemistry alone is a short-term answer to a long-term chronic problem,” says Jeff Tomberlin, extension livestock entomologist at Texas A & M University. Relying on insecticides alone for long-term fly control is raft with problems. Insecticide resistance tops the list.

The other misconception about spraying is that it doesn’t cost that much. Producers think that the labor cost to implement an IPM program will far outweigh the cost of spray. But research shows that quite the opposite is true.

Develop a long-term plan
When it comes to selecting a fly-control program, you want one that offers a sustainable line of defense, says Tomberlin. Sustainable means the program offers long-term control that will suppress the fly population and take advantage of any naturally occurring beneficial arthropods. When you use good sanitation and management practices to complement Mother Nature, you can actually reduce fly populations to the point that chemical controls are rarely, if ever, needed.

Take, for example, a 2,500-cow dairy just north of Chino, Calif. It relies on sanitation to limit the breeding areas for flies, plus uses bait stations and scatter baits to control the fly population. The dairy does not have to use sprays, says Doug Van Gundy, manager of specialty field development with Wellmark International. Despite having a lot of urban encroachment in the area, the dairy is happy with its fly control — and so are its neighbors. 

Avoid resistance
With sprays, fly resistance can be a big problem. Rotating between different classes of insecticides can help, but it won’t prevent insect resistance from occurring, says Wes Watson, extension entomologist at North Carolina State University. And, if you spray on a calendar basis, such as once a week, instead of on an “as needed” basis, flies can develop resistance rather quickly.

For example, flies can become resistant to pyrethroids in as little as two to three years, says Van Gundy. And with all of the products that have been taken off of the market recently, just two types of spray products remain — pyrethroids and organophosphates.

And some of them could still go away. Under the 1996 Food Quality Protection Act, the Environmental Protection Agency was ordered to re-evaluate all pesticides for worker safety and food safety. Several pesticide products were not re-registered, and the EPA is just now starting to re-evaluate the organophosphate and pyrethroid products.

“When a producer tells me he only uses sprays for fly control, the first question I ask is, ‘Does it still work?’” says Don Rutz, entomology department chair at Cornell University.  And the next question he asks is, “How often do you spray?” If the producer sprays on a regular basis, he probably has a resistance problem, but doesn’t know it.

When you ask a producer how often he sprayed 10 years ago, compared to five years ago and a year ago, most realize that they now spray more often, says Kaufman. Since resistance occurs over time, it’s difficult to spot it unless you’re looking for it. (See a “Quick resistance test” at right.)

Most producers who rely on insecticides say they get “good knock-down.” That’s because flies that have developed resistance still get stunned by the spray, but they also get up and fly away later. And each fly that survives passes the resistant genes onto its offspring.


Baits and sticky traps are important components of an IPM program.

IPM is your best bet
Integrated pest management (IPM) uses a multi-faceted program — including the judicious use of sprays — to deliver fly control. In fact, many dairies that use IPM don’t ever spray, says Watson. But IPM isn’t about eliminating the use of sprays. Quite frankly, sprays are sometimes needed. 

Here’s how IPM works: Identify your target, eliminate its breeding areas, monitor fly populations, use cultural controls such as baits, tapes and traps, and biological controls such as parasitic wasps to suppress the fly population and then, only when necessary, use sprays.

In order to demonstrate that IPM really works, researchers at Cornell University have measured IPM dairies against dairies that rely on spray programs for fly control.

Here’s what they have found:

  • A study of 26 New York and Maryland dairy farms revealed that, on average, the fly population on dairies using IPM was about half that of farms which did not use IPM.
  • Dairies that implemented IPM programs reduced insecticide treatments by 80 percent.
  • Sanitation efforts that target the most prolific fly breeding areas — calf pens, maternity and sick pens — can reduce fly populations by up to 90 percent.
  • IPM is a more cost-effective fly control program on a per-cow basis than the use of sprays. 
  • In the long run, IPM can help reduce or delay insecticide resistance.

IPM isn’t as labor-intensive as many producers think. It doesn’t involve daily cleaning; rather, it’s cleaning as infrequently as every seven days to break the fly life cycle. By focusing their efforts on sanitation, as part of an integrated IPM program, most producers become believers. But the minute you stop following your IPM plan, things change quickly.

Take, for example, the New York dairy that had a stable fly problem. With Kaufman’s help, when it adopted an IPM program and eliminated the use of sprays, it saved about $400 a month. Things improved dramatically until the dairy hired a new calf manager. The new manager re-instituted the practice of dumping calf water in the calf stalls. Within 20 days, the fly population mushroomed, and the farm was back in the same boat it was in a few years earlier. Once the employee stopped dumping the leftover water in the calf pens, the fly population dropped.

For more information: http://www.entomology.cornell.edu/Extension/Vet

Quick resistance test

use this test to determine if you have any resistant flies on your farm. The next time you go out to spray the barn, place a couple of pieces of cardboard on the floor, suggest Phil Kaufman, extension entomologist at Cornell University. Spray and then return one hour later to count the number of flies on each piece of cardboard. Then, return six hours later to count  the number of flies on each piece of cardboard again. If any flies are missing, you have some insecticide resistance.