by: Dr. Brandi Bourg Karisch
Ext. Beef Cattle Specialist, Mississippi State University

As temperatures start to rise, and we enter the heat of the summer months, it is important to have a strategy in place to control and limit the negative effects of flies on the herd. Although the horn fly is a relatively small pest, it can eat a big hole in an operation's profits. Considering just one pest, the horn fly, previous estimates have production losses estimated over $730 million for the beef industry. These production losses come from a variety of factors, such as blood loss, toxicity, and diseases. These will ultimately result in production losses seen in the form of reduced performance, reduced feed efficiency, and reduced milk production. Average daily gains in stocker cattle have been estimated to be reduced by over 13 percent with high infestations of horn flies. Ultimately, these losses add up to reduced profits for beef producers, and with the large losses in mind prevention strategies become very valuable.

There are many options available for fly control, and the best method may vary from one producer to the next. Many factors should be considered when choosing which method will work best for an operation. While price is often the first factor considered, effectiveness, ease of use, and reapplication rates must also be considered. When considering the value of control, it is important to consider threshold fly levels. There are two threshold levels to consider, the threshold where treatment is required and the economic threshold, or the number of horn flies per animal at which value of damage is equal to the cost of control. These two thresholds differ greatly. Fifty flies are typically the level where treatment is considered required, whereas the economic threshold is 200 flies per cow.

The life cycle of the horn fly is important to understand. The horn fly is a blood feeder that lives on back, belly, and legs of the host. The life cycle begins when the female fly leaves the host animal for only a few seconds to lay eggs in fresh manure. The eggs then hatch in one to two days into larvae. The larvae will feed and grow in the manure for three to five days, before change into pupae In the manure or soil for six to eight days. The adult fly will then emerge and begin feeding on the nearest host animal. Although the life of the female fly is only two to four weeks, she spends day and night feeding on blood from the host animal. Flies feed for 10 to 25 minutes at a time, and may feed up to 40 times per day. Fly control methods target the life cycle of the fly at various stages.

Fly control options take on a variety of forms, including self-application devices, pour-ons, ear tags, and feed through. Within each of these classes, there are a wide range of choices available with differing insecticides, costs, and effectiveness associated with each. It is first important to understand the major differences associated with each form.

Self-application devices are typically either back rubs or dust bags. Each device is treated, or “charged” with an insecticide diluted in oil, and placed n a high traffic area of the pasture. There are several benefits to these types of systems. The majority of these benefits are associated with self-treatment, in that cattle experience little stress and there are minimal labor inputs involved in the application process. However, the disadvantages associated with these devices are also associated with their self-treatment nature. A non-uniform treatment may be observed, and some animals may refuse to pass through these devices and would therefore be untreated. Also there is the question of when to recharge these devices.

Fly tags, or ear tags impregnated with an insecticide, are another option for fly control. The tags are typically recommended to be placed two per animal, with the recommendation to re-tag when fly counts begin to rise at a rapid rate. Benefits of this option include a relative ease of use, and low labor and stress when incorporated into routine working times. One major disadvantage is that resistance can develop with improper use, which occurs when the type of insecticide in the tags are not rotated. For producers without access to a good set of working facilities, this method may not be an option.

Pour-on or spray-on insecticides are another option for fly control. These products require direct application, and many are labeled to treat both internal and external parasites. There are several benefits to using this application technique. First, the direct application assures that every animal is treated. When used properly, sprays and pour-ons are highly effective, and offer the ability to combine fly control with internal parasite treatment. The disadvantages of using sprays and pour-on treatments are an increased stress on animals due to the application process, and also may not be an option for producers who do not have access to an area to pen and/or work cattle. As also noted with fly tags, resistance may be a problem if insecticides are not properly rotated, and one insecticide is used continuously.

The newest method of fly control involves feed through products. With this method, an insecticide designed to prevent larvae from reaching maturity is mixed into a feed or mineral source for the cattle to consume, and typically works best if it is fed before the adult flies begin to emerge. The major benefits of the feed through option are attributed to its application method. Since the fly control is present in the feed or mineral cattle would already be consuming, there is little extra labor or stress involved for the cattle. Some disadvantages of this option include consumption, the product is not effective if cattle do not consume it in adequate amounts, and fly transfer, if cattle are near other animals not treated for flies, and it is likely that adult flies will transfer to the treated herd. It is important to remember that these feed through products reduce fly counts by interrupting the life cycle of the fly not by killing adult flies.

With so many options available for fly control, and so many different products available within each option, the task of choosing the right method for your operation may seem daunting. It is important to consider the labor involved and inputs needed for each method, and choose the method which best suits your operation. With any method chosen, it is also important to remember to rotate the active ingredients in your chosen method, to prevent flies from developing a resistance to a particular insecticide and decreasing its effectiveness. Lastly, remember that the benefits seen when cattle are treated for horn flies when fly loads have reached a critical level will far outweigh the costs associated with that control.

For more information about beef cattle production, contact an office of the Mississippi State University Extension Service, and visit msu-cares.com/livestock/ beef.

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