Forced-use back rubbers can be used to help control horn flies in dairies. (Photo by Dr. Phillip Kaufman, University of Florida IFAS Extension)
Forced-use back rubbers can be used to help control horn flies in dairies. (Photo by Dr. Phillip Kaufman, University of Florida IFAS Extension)

Horn flies are one of the livestock pests with the greatest impact on the health and productivity of cattle. In the U.S., annual losses to horn fly damage total between $700 million and $1 billion.

Horn fly damage is caused by blood feeding. The flies feed frequently and exclusively on blood, piercing the skin of cattle with their proboscis and taking around 20 small blood meals each day. Pain and irritation due to the constant presence of the flies and their bites cause defensive behavior in cattle, which prevents adequate food consumption and rest.

Observing cattle behavior should give a warning of horn fly or other biting-fly activity. Cattle being bothered by horn flies will lick and twitch their skin, switch their tails and kick at their bellies.

The number of horn flies per animal may be easily estimated in both sunlit or shade conditions. Animals should be selected randomly, and estimates should be made for 10 animals per herd. Experimental results indicate that 50 flies per side on a dairy cow or 100 flies per side on a beef animal is the economic threshold.

The close association of horn flies with cattle (the flies leave the host only to lay eggs or to relocate to a new animal) makes horn flies particularly suitable for on-animal chemical-control measures.

In a number of states, however, the flies have developed resistance to some of the insecticides found in ear-tag formulations. Check with your local Extension educator, veterinarian or animal-health supplier to determine which treatments should be used for horn fly control in your area.

Several different methods can be used to apply insecticide to cattle for horn fly control, but ear tags and forced-use dust bags provide the best control. Self-treatment methods such as dust bags and back rubbers will provide control, although back rubbers are usually less successful on horn flies.

For self-treatment devices to be effective, cattle must be “forced” to use them. For example, dust bags may be hung in exit alleyways from barns or placed between pasture and water or feed sources.

Sprays and dips also may be used successfully for horn fly control. Application of residual sprays must reach 1 to 2 qt. per animal at 150 to 200 psi to ensure complete coverage of the animal and penetration to the skin.

Animals should be treated in small groups to ensure that all animals receive an even application of the treatment.

The immature stages of the fly may be controlled in the manure by the application of feed-through additives. The effect of immature fly control, however, may not result in a decline in the adult population because flies emigrate from neighboring areas.

A walk-through trap is a non-chemical method of control that collects and kills horn flies directly from cattle. The animals must be “forced” to pass through the trap regularly as with the other self-treatment options described above.

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