Use more than one approach for fly control.
Flies cause substantial economical losses to cattle producers. For example, biting flies carry diseases such as anaplasmosis and bovine leukosis virus, while face flies can spread pink-eye from animal to animal. Unfortunately, you will never completely eliminate fly problems in your herd. Flies are well-adapted to the environment; they have been around for thousands of years and are doing very well for themselves.
The adaptability of flies means that it is going to be impossible to completely remove them from your operation. However, there are ways to control flies and to lessen their negative impact. These practices each have their benefits and drawbacks. Using a combination of these practices can improve control.
You should evaluate your herd, your environment and your fly pressure to choose which is best for your livestock.
Feed an insect growth regulator or a larvicide
There are a variety of these products available, depending on your needs. They include Altosid for horn flies, or Rabon for horn, face, house and stable flies. ClariFly is product used mainly with confinement cattle. The larvicide or insect growth regulator should be fed starting 30 days before flies typically appear, and should be continued for 30 days after a killing frost. This means feeding the product from about mid-March to mid November. While horn flies don’t travel far, face flies will travel a mile or two. This means that if your neighbors have cattle, you may inherit some of their flies—unless they have joined the fray and are aggressive about knocking down fly populations.
Use fly tags
Newer-generation fly tags are useful in controlling fly populations. To reduce pyrethroid resistance, after using pyrethroid tags for two consecutive years, switch to an organophosphate tag for one year. For optimal fly control, many products require two tags for an adult animal and one tag for a calf. As always, whenever you are using a pesticide, read and follow label directions. The rules governing pesticide and insecticide are federal rules. You really don’t want to run afoul of them.
Applying the tags too early will result in less effective fly control. The ideal time to apply tags is when there are about 200 horn flies per cow. The best time to check this is in the early morning hours. Mornings are cooler, and the wind tends to be calm. Observe livestock while the animals are up and grazing. It is relatively easy to see the flies on their sides.
Pour-ons require labor, but are effective fly deterrents. You can apply a pour-on at the same time you fly-tag your cattle. If you do this during spring turnout, you can use a product that kills internal parasites, as these products are also effective against flies. If you apply a pour-on later in the year, use products that are just labeled for flies and/or lice.
Provide dust bags/cattle rubs
If you place a dust bag or rub at a site where all cattle use it, keep it charged with insecticide. Rubs are an economical means of controlling face and horn flies.
If you use a spray product on your cattle at timely intervals, it can be very effective at reducing the fly population. Though useful, it is time consuming, and control can be sporadic.
When working on controlling flies and lessening their damage to your cattle, it is unlikely that one strategy alone will be sufficient. When you use several methods in conjunction, you are better able to lessen the negative impact of flies.