Pasture Flies and Ear Tags for Cattle

Horn and face flies are two of the more problematic insect pests to manage in pastures. Without proper management, they can reduce cattle weight gain. Insecticide-impregnated cattle ear tags are practical, easy to apply, and can provide long term control of horn flies and some reduction in face fly numbers when used properly.

Figure 1. Try to keep horn fly numbers below 100 per side of animal (Photo: Craig Sheppard, University of Georgia,

It is important to not apply the ear tags too early in the season as the insecticide levels provided by the tags will slowly diminish during the season. Tagging too early in the season can mean that the tags are not providing good control in the fall that will help to control the overwintering population. Poor fly control late in the season can increase the risk of resistance development to the insecticide group used in the tags.  For fly control, it is best to tag animals after horn fly numbers reach 100 or more per side. This reduces the chances of developing resistance to the active ingredients that are being used. Normally, tags provide 12 to 15 weeks of fly control. Ear tags do not control face flies as well, but help to reduce their numbers.

Pastures flies will develop resistance to the active ingredient in ear tags if tags with the same mode of action are used year after year. Keep in mind that each insecticide belongs to a specific mode of action group that attack at a specific site in the pest. Continual use of products in the same mode of action group can lead to insecticide resistance in horn fly populations. Rotation among these groups is an important part of an insecticide resistance program, with a three-rotation among modes of action recommended.

Besides era tags, there are several other systems that can be put in place so that cattle can treat themselves with insecticides for horn fly and face fly control, generally in an effective and economical manner. Dust bags and oilers/back rubbers can be made or purchased. In addition, there are spray systems that can be incorporated into mineral stations or triggered as animals pass through gaps in fences between pastures. One advantage of ear tags is that the control system moves with the animals. This may be an advantage with rotational grazing where dust bags or back rubbers are not in place in every pasture or grazing area.

Protect yourself by wearing nonpermeable gloves when tagging animals. The concentration of insecticide in the tags varies from 8% to 36%. The tags are manufactured so that the insecticide is rubbed off the surface and onto the animal. Any handling of the tags leaves some insecticide on the hands. The insecticide then can be transferred easily to the mouth, eyes, face, or other areas of the body. Some individuals may be very sensitive to the active ingredients in the tags and several products carry statements about the potential for allergic reaction. Many are easily absorbed through the skin or eyes, and some have irritation vapors. Signal words on the label range from CAUTION to WARNING. So, wear protective gloves and wash hands thoroughly with soap and water after tagging or when taking a break.

Ric Bessin, Extension Entomologist

Posted in Livestock Pests
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