Every spring, our thoughts turn from calving season to breeding season, green grass, rainy days and warmer temperatures. But with the growing pastures and pleasant temperatures come some disadvantages as well - fly season is upon us.

Are flies bugging your cattle?Flies will be abundant by the time this News and Views article hits your mailbox. At the time of writing this article in late March, I already have noticed a large number of flies on livestock. If you have not already started a fly control program for this year, you are probably already behind the curve. With the early spring rains, 2008 promises to be favorable for insects.

Flies are a nuisance for humans, but an even greater nuisance for livestock. Additionally, flies can spread disease, from anaplasmosis to pink eye. They are also 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, standing in groups or in the middle of a stock pond.

It doesn't take a large number of flies to have an impact on your cattle's production. As few as 100 to 200 flies per side is enough to impact stocker gains by 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 to be a problem.

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

The following are a few thoughts on the various control methods:

  • Pour-ons and sprays provide a good initial kill with two to six weeks' residual. Sprays will typically wear off faster. Rainfall or 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-two weeks or after a rain.
  • 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.
  • Feed additives are effective in stopping the fly life cycle. But one of the biggest obstacles 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 effective. Some feedlots have started using this method as the fly wasps are considered a natural, nonchemical method of control. Since they are weak fliers, the wasps must be placed in areas of high manure concentration, i.e., feedlots or horse stables. They do not reproduce so they have to be replenished monthly during the fly season.


Remember to follow label directions and applicable withdrawal times prior to slaughter. Getting in control of your fly problem will make your cattle more comfortable and your wallet happier.

Source: Robert Wells