Losses Associated with Flies
Flies annoy and irritate animals, transmit disease, reduce weight
gains, and reduce milk production.
Horn flies can cause significant economic losses. They are biting,
blood-sucking flies that feed 20 to 40 times per day, reducing
milk production up to 20% and decreasing gains in growing cattle
by 0.25 to 0.5 lb per head daily (USDA) if not controlled. Five
hundred horn flies per animal will consume about 1 gallon of blood
in a 30-day period.
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Stable flies can do as much if not more damage than horn flies.
Stable flies feed with a piercing-sucking mouth. According to the
University of Illinois, as few as 40 flies per animal can cause
significant reduction in milk production. The USDA estimates milk
production losses at up to 20% without good control.
Economic losses may occur when the fly population reaches 100
flies per animal. Over 200 flies per animal can cause significant
economic losses. A good fly control program using an oral
larvacide, backrubber at peak season, and time-released
insecticide provides a favorable cost:benefit ratio.
Fly Control Management Recommendations
Practice good sanitation management.
Keep fly populations under control.
Elimination is not the goal. Treat fly levels over 100 flies per
animal. Keep the population below 200 flies per animal.
Use periodic treatments, rotating
insecticide methods (sprays, dust, backrubbers).
Use an oral larvicide with periodic
treatments for cattle on pasture.
To reduce over-winter fly phase, treat
late in the fly season.
If using insecticide tags as part of
the pest control program, follow usage recommendations throughout
Use a pyrethrin for quick kill and
reduction of all fly populations.
Insecticide ear tags were introduced
in the early 1980s. Originally, they were very effective; however,
favorable results lasted only a few years. Due to management
practices and other factors, resistance to the insecticides used
in ear tags quickly developed.
Resistance to man-made pesticide
compounds (pyrethroids, organophosphates, etc.) can occur in a
specific fly population.
Resistance can be widespread, but not
The flies' resistance mechanisms are
different for different compounds.
Insecticide resistance is often
perceived rather than actual due to inadequate application, poor
timing, inadequate total control program, and/or sudden resurgence
of flies if conditions are ideal.
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