#Livestock Horn Fly Management

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With summer grazing season almost here, now is the time to prepare a horn fly management plan. Developing an effective plan requires some knowledge about the fly’s habits, life cycle, economic impact, and available control strategies.

United States livestock producers lose over $1 billion annually to the horn fly, making it one of the most damaging ectoparasites of pastured cattle. Horn fly feeding cause’s dermal irritation, anemia, decreased feed intake leading to reduced weight gains, and diminished milk production. Horn flies have also been implicated in the spread of summer mastitis. Furthermore, an estimated $60 million is spent annually on insecticidal control. Studies conducted in Nebraska have established calf weaning weights were 10-20 pounds higher when horn flies were controlled on mother cows. The horn fly also affects yearling cattle reducing yearling weights by much as 18 percent. The economic injury level (EIL) for horn flies is 200 flies per animal. An economic injury level is when the economic impact of the pest equals treatment costs. During the summer horn fly numbers on untreated Nebraska cattle can exceed several thousand.

Horn flies are small in size, approximately 3/16” in length and are usually found on 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 female, acquire more than 30 blood meals per day. 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. read more…

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