By Dave Boxler, Nebraska Extension Educator
As we transition into spring and before livestock producers turn cattle in to summer pastures, selecting this year’s fly control program should be considered. A thought to consider, did your fly control program work last year? If it did not, now is the time to consider a different method. There are many fly control options and strategies available to Nebraska livestock producers to help manage the three fly species that economically impact grazing cattle; the horn fly, face fly and stable fly.
Horn flies are small in size, approximately 3/16” in length and are usually found on the backs, sides and poll area of cattle. During a warm summer afternoon they can be found on the belly region of cattle. Horn flies, both male and females flies acquire more than 30 blood meals per day (Figure 1 http://go.unl.edu/ymm7). 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 upon the weather.
Economic losses associated with horn flies are estimated at more than $1 billion dollars annually in the United States. Horn fly feeding causes irritation, blood loss, decreased grazing efficacy, reduced weight gains and diminished milk production in mother cows. Additionally, horn flies have been implicated in the spread of summer mastitis. Studies conducted in the U.S. and Canada have shown that horn flies can cause weight gain loss in cattle, and calf weaning weights can be negatively impacted from 4 – 15 percent. Studies conducted in Nebraska have established 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 affected by the horn fly; other studies have shown yearling weights can be reduced by as much as 18 percent.
There are many insecticide control methods available to manage horn fly numbers; backrubbers, dust bags, insecticidal ear tags and strips, pour-ons, oral larvicides, low pressure sprayers, mist blower sprayers and the Vet Gun™. Backrubbers and dust bags are an effective way to reduce horn fly numbers if cattle are forced to use them. Insecticide ear tags and strips are a convenient method of horn fly control. However, many horn fly populations in Nebraska exhibit a degree resistance to the pyrethroid class of insecticides. The recommended management practice to maintain horn fly control is to rotate insecticide classes. Animal sprays and pour-on products will provide 7-21 days of control and will need to be re-applied throughout the fly season. Oral larvicides prevent fly larvae from developing into adults. An important factor when using an oral lavicide is insuring steady consumption. An additional complicating issue using an oral larvicide is horn fly migration from neighboring untreated herds which can mask the effectiveness of an oral larvicide. The Vet Gun™ applies an individual capsule of insecticide to an animal and can provide control between 21 and 35 days.
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. The adult female face flies clustering around an animal’s eyes, mouth and muzzle, can cause extreme annoyance (Figure 2 http://go.unl.edu/9beh). Face flies will also feed on blood and other secretions around wounds caused my mechanical damage or other injury. Face flies are present throughout the summer but populations usually peak in late July and August. Face flies are most numerous along waterways, areas with abundant rainfall, canyon floors with trees and shaded vegetation, and on irrigated pastures.
Female face fly feeding causes damage to eye tissues, increases susceptibility to eye pathogens, and 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 essential in reducing most pinkeye problems.
Achieving adequate face fly control can be difficult because of their habit of feeding around the face and the significant time they spend off the animal. Control is maximized when the cattle receive daily insecticide applications by either dust bags, oilers, sprays, or an insecticide impregnated ear tag/strip. Ear tags/strips should be applied at the label recommended rate. Both cows and calves must be treated if control is to be achieved. Pinkeye vaccines are available and should be considered if face flies and pinkeye have been a recurring problem. Currently, commercial and autogenous pinkeye vaccines are available; please check with your local veterinarian about the use of these products in your area.
Stable flies are serious pests of feedlots and dairies and of pasture cattle. The stable fly is a blood feeder, mainly feeding on the front legs of cattle, staying on the animal long enough to complete a blood meal (Figure 3 http://go.unl.edu/y0of). Their bites are very painful; cattle will often react by stomping their legs, bunching at pasture corners, or stand in water to avoid being bitten. Stable flies cause similar weight gain losses to both pasture and confinement cattle. University of Nebraska research, recorded a reduction in average daily gain of 0.44 lbs. per head with animals which received no insecticide treatment compared to animals which received a treatment. The economic threshold of 5 flies per leg is often exceeded in Nebraska pastures.
The female stable fly deposits eggs in spoiled or fermenting organic matter mixed with animal manure, soil and moisture. The most common developing sites are in feedlots or dairy lots, usually around feed bunks, along the edges of feeding aprons, under fences and along stacks of hay, alfalfa and straw. Grass clippings and poorly managed compost piles also may be stable fly developing sites. Winter hay feeding sites where hay rings are used can often be a source for larval development through the summer if the proper moisture is present. The life cycle of the stable fly can take 14-24 days in Nebraska, depending on weather conditions. While the source of early season stable flies on pastured cattle it not well understood some probably develop from larvae overwintering locally. Other early season flies may be migrants from southern locations, but evidence is lacking. Nevertheless, we do know that stable flies can move at least 10 miles or more.
The only adult management option available for the control of stable flies on range cattle is use of animal sprays. Sprays can be applied using a low pressure sprayer or can be applied with a mist blower sprayer. Weekly applications of these products will be required to achieve reduction in fly numbers. Sanitation or clean-up of wasted feed at winter feeding sites may reduce localized fly development. If sanitation is not possible these sites may be treated with a larvicide (Neporex®). But, the application of either procedure may not totally reduce the economic impact of stable fly feeding.
For Current Nebraska control recommendations check EC1550, Nebraska Management Guide for Insect Pests of Livestock and Horses at: http://entomology.unl.edu/livestock
When applying any insecticide control products, please read and follow label instructions.
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Managing Pasture Flies
By Dave Boxler, Nebraska Extension Educator