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Reducing Fly Numbers on Pastured Cattle

May 15, 2014

As late spring approaches, livestock producers should evaluate and select pasture fly control options available for their specific management system.
By: Dave Boxler, Extension Educator, University of Nebraska-Lincoln

There are three fly species in Nebraska and much of the United States which could economically impact pastured livestock: the horn fly, face fly and stable fly.

Horn Flies
Horn flies are about 3/16" in length and are normally found on the backs, sides, and poll areas of cattle. During the warm part of the day horn flies can be seen on the belly of cattle. The horn fly feeds on blood with both male and female flies acquiring some 20 to 30 blood meals per day.

horn flies on cow
After mating the female fly will leave the animal to deposit eggs in fresh cattle manure. Eggs hatch within one week, and larvae feed and mature in the manure, pupating in the soil beneath the manure pat. Newly emerged horn flies can travel several miles searching for a host. The entire life cycle can be completed in 10 to 20 days depending on the weather.

Economic losses associated with horn flies are estimated at more than $800 million annually in the United States. Horn fly feeding causes irritation, blood loss, decreased grazing efficiency, reduced weight gains and a decline in milk production. Furthermore, horn flies have been implicated in the spread of mastitis.

Many studies have been conducted in the U.S. and Canada to assess the economic effects of horn flies on cow and calf weaning weights. Nebraska studies have demonstrated calf weaning weights were 10 - 20 pounds higher when horn flies were controlled on mother cows. The economic injury level (EIL) for horn flies is 200 flies per animal. Yearling cattle can also be impacted by the horn fly; other studies have indicated yearling weight can be reduced by as much as 18 percent.

Horn Fly Control
There are many chemical application methods available to reduce horn fly numbers; backrubbers, dust bags, insecticidal ear tags, pour-ons, oral larvicides, and sprays.

Insecticide ear tags are a convenient method of horn fly control. Because many horn fly populations in Nebraska are resistant to pyrethroid insecticides it is important to rotate insecticide classes yearly for ear tags and seasonally for other application methods. To achieve maximum performance from insecticide ear tags, two tags per animal are required. Delaying ear tagging until June 1st will provide the greatest degree of control.

Backrubbers and dust bags are an effective way to reduce horn fly numbers, if cattle are forced to use them.

Sprays and pour-ons will provide 7-21 days of control and will need to be repeated throughout the fly season for effective control.

Oral larvicides prevent fly larvae from developing into adults. An important factor when using an oral larvicide is insuring daily consumption. A complicating issue when using an oral larvicide is horn fly immigration from neighboring untreated herds which can mask the effectiveness of an oral larvicide.

Face Flies
Face fly adults closely resemble house flies except they are slightly larger and darker than the house fly. The face fly is a non-biting fly that feeds on animal secretions, nectar and dung liquids. Adult female face flies typically cluster around animal's eyes, mouth and muzzle, causing extreme annoyance. They are also facultative blood feeders; gathering around wounds caused by mechanical damage or other injury.

face flies

Face flies are present in the field throughout the summer with populations usually peaking in late July and August. Face flies are most numerous along waterways, areas with abundant rainfall, canyons where the canyon floors have trees and shaded vegetation, and on irrigated pastures.

Feeding of the female face fly around the eyes causes eye tissue damage, which creates susceptible tissue for eye pathogens. In addition to annoyance, female face flies vector Moraxella bovis, the causal agent of pinkeye or infectious bovine keratoconjuctivitis. Pinkeye is a highly contagious inflammation of the cornea and conjunctiva of cattle. If coupled with the infectious bovine rhinotrachetis (IBR) virus, M. bovis can cause a much more severe inflammatory condition.

Controlling face flies is a key to reducing most pinkeye problems.

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