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Are flies bugging your cows?Are flies bugging your cows?

Flies come around every year, and so must fly control.

April 7, 2020

3 Min Read
Fly control
Fly season means annoyance and irritation for even the toughest-hided bull — or rancher, for that matter. For your cows and calves, flies can become more than an annoyance and irritation, however. Flies can transmit diseases like pinkeye and can cause decreased production potential for your cattle. Courtesy of Noble Research Institute

Every spring, our thoughts turn from calving to the breeding season, green grass, rainy days and warmer temperatures. However, with the green grass and pleasant temperatures come some disadvantages as well — fly season is upon us. If you have not already started planning your fly control program for this year, you are probably already behind the curve.

Flies are not only a nuisance for humans, but also an even greater nuisance for livestock. Additionally, flies can spread disease, from anaplasmosis to pinkeye. They are responsible for a tremendous amount of lost production in the form of decreased weight gain or lower milk yields. Rather than eating, cattle will spend time stomping and tail swishing, lying down, and standing in groups or in the middle of a stock pond. 

It doesn’t take a large number of flies to have an effect on your cattle’s production. As few as 100 to 200 flies per side is enough to impact calf or stocker gains by 25 to 50 pounds during the summer. This is greater than or comparable to the weight gain achieved through a growth implant program. If you can see more than a hand-sized patch of flies on each side — typically behind the shoulders of your cattle — there are enough there to be a problem.

Fly control methods

Related:It’s summer, and the fly wars are on

There are many control methods out there. Some of the more common methods are pour-ons, sprays, rubs or dusters, ear tags, feed-through additives and biological controls. Some methods work better than others, and each has its place. Using a combination of methods will afford you the most effective control. Additionally, remember to change the chemical class or family you use periodically to reduce resistance.

Pour-ons and sprays provide a good initial kill with two to four weeks of residual activity. Sprays will typically wear off faster. Rainfall, excess sweating or the cattle lingering in stock tanks reduces the duration of protection.

Rubs and dusters are an effective method of control once the cattle associate the use of the applicator apparatus to a reduced insect load. It is best to place the applicator next to mineral feeders, water sources or an area that will force the cattle to rub up against it. Additionally, the chemical will need to be recharged once every one to two weeks, or after it rains.


Ear tags are a very effective season-long treatment, but remember to cut the tags out at the end of the season. Leaving the tags in builds resistance to the chemical. Change the active ingredient from year to year. If you used a synthetic pyrethroid this year, change to an organophosphate or organochlorine tag next year.

Related:Remember these keys for successful fly control

Feed additives are an effective means of stopping the life cycle of the fly. One of the biggest obstacles, however, is ensuring consistent and adequate intake of the product to have effective control.

Biological control in the form of fly wasps, sometimes called fly predators, is also an effective method. Some dairies and feedlots have started using this method, as the fly wasps are considered a natural, non-chemical control method. Since they are weak flyers, the wasps must be placed in areas of high manure concentration, such as drylots, feedlots or horse stables. They are sterile, so they have to be replenished monthly during the fly season. 

Always remember to follow label indications and applicable withdrawal times prior to slaughter. Getting in control of your fly problem will make your cows more comfortable and your wallet happier.

Wells, Ph.D, Professional Animal Scientist, is a Noble Research Institute livestock consultant. Contact him at [email protected].

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