Insecticide impregnated cattle ear tags have been a popular means of pasture fly (horn fly and face fly) control for over 20 years. The insecticide in them is transferred to the animal’s hair coat as it grooms and rubs. Insecticide protection lasts for 12 to 16 weeks and the fly control program travels with the animal as it goes from pasture to pasture.

Rotation of insecticides from year to year is recommended to reduce the chance of a problem with insecticide resistance, especially in horn fly populations. This shows up in the form of a shorter than normal period of fly control. Changing tag brands is not enough; insecticides used in a rotation strategy must have a different mode of action than the previous product. Tags containing insecticides representing four different modes of action are available now and there are some combination tags that contain two different types in the same product.  

However, reduced fly control can be caused by several different factors.

Some examples:

1) Tagging too early. The 12-16-week fly control clock starts when tags are inserted. Tagging very early in the spring can mean protection runs out before fly season is over.

2) Horn flies moving in from untreated nearby herds can keep pressure high and make control seem less effective.

3) Above normal rainfall can keep manure wetter longer, and more suitable for horn fly breeding than during hot, dry summers when manure dries quickly and may less hospitable for the maggots.

Here are some ways to get the most out of your ear tag-based pasture fly control program in 2010.

1) Rotate insecticide classes annually. Check the active ingredient in the tag to be sure you know what you are using and record the choice each year. The Insecticide Recommendations for Beef (ENT 11) lists the tags by insecticide class. This makes it easier to establish a rotation.

2) Apply tags after horn fly numbers reach about 100 per side per animal. This will keep them from being applied too early. It takes more than 100 flies per side to have an impact on weight gain.

3) Supplement fly control with dust bags, oilers, sprays or pour-ons, if needed. Staying on a pro-active program will keep resistance problems at bay.

Feed additive insecticides for cattle fly control

Horn flies and face flies breed in cattle droppings in pastures. This is a weak link in the life cycle of these pests because the maggots are concentrated in the manure before they emerge as adults and attack animals. Manure piles are scattered over pastures; elimination of them or treatment of individual piles is impractical. However, manure can be made toxic if the animals consume an oral larvicide.

Mineral blocks or loose supplements are available which contain either the organophosphate insecticide or an insect growth regulator. Organophosphate insecticides work upon the nervous system of an insect, killing it quickly. An insect growth regulator interferes with the development of the insect, specifically the molting process. Every animal in the herd must consume at least a minimum effective dose for the manure to be toxic to the flies.

These larvicides are labeled for horn fly control so other measures must be taken if face flies are a problem, too. Feed-thrus are only a part of a total pasture fly control program because horn flies and face flies will move in from nearby herds. Supplemental control though the use of dust bags or backrubbers is needed to deal with these fly-ins. (Source: Lee Townsend, University of Kentucky)

Educational programs of the University of Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.

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