Flies cost the cattle industry more than $500 million each year, causing slowed weight gain, reduced milk production and diseases such as pinkeye and anaplasmosis. Effective fly control may require combined use of products, said a University of Missouri Extension livestock specialist.

The recommended economic threshold for a pesticide program is 200 flies per animal, said David Hoffman.

Face and horn flies are the two most common types that attack cattle, said Hoffman said. Face flies spread bacteria that cause pinkeye, reducing average weight gain in calves by 17 pounds when one eye is infected and 30 pounds to 65 pounds when both eyes are infected. Because these insects spend little time on the animal, they are difficult to control with pesticides.

Horn flies feed up to 30 times per day, primarily on the back and shoulders of cattle. The pest spends its entire life cycle on the animal, leaving only to lay eggs in fresh manure.

Insecticide application methods for controlling flies include ear tags, sprayers, back rubbers, dust bags and pour-on and oral application.

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