ST. CLOUD, Minn. — Horn flies are the number one economic ectoparasite in North American cattle production, it is estimated that $1 billion is loss annually. (Byford, R.L., Craig, M.E., Crosby, B.L., A review of Ectoparasites and Their Effect on Cattle Production, J. Anim. Sci., 1992, 70:597-602) So how do you know if you have a fly problem? Take a look at your herd the next time you are out checking them, are they bunched up, do they have more than 200 flies on their backs? These can be triggers that can warn you that there may be a problem. There are many ways to come at this issue and many products out there to help combat the horn fly.
One of my favorite ways to deal with this problem is to feed a fly control product through the mineral or feed. IGR is ingested by the cattle through the mineral or feed and as they graze cattle disperse the IGR through their manure. Adult horn flies live for 2-4 weeks taking 20-40 blood meals per day. The female flies leave the animal for a few seconds to lay eggs in fresh manure (must be less than 5 minutes old). In 1-2 days the eggs hatch into larvae, 3-5 days the larvae molt into pupae and then the pupae molt into adults in 6-8 days. This is where IGR breaks that life cycle, preventing the adults from emerging. Methoprene (Altosid) is the product that is used on pastures that can be in mineral, tubs or blocks. If your cattle are in a confined situation you can use the product diflubenzuron (Clarify). One of the main questions we get is when do you start feeding IGR and when do you stop? What is recommended is 30 days before pasture and 30 days after the first frost.
The other effective ways at controlling flies are dust bags, back-rubbers (oilers), animal sprays, pour-ons, and insecticide impregnated ear tags.
* For dusts some that are recommended are tetrachlorovinphos (Rabon) and permethrin (many brand names).
* Back-rubbers control products recommended are permethrin (many brand names) and phosmet (Prolate). These two methods have been shown to work best in force used situations.
* Animal sprays can be effective, but the drawback is increased cattle handling, cost and added stress to the cattle during the fly season.
* Pour-on insecticides are ready to use formulations applied along the back line of cattle. Although they will control flies it is for only short periods. Products recommended are permethrin and macrocyclic lactones (ivermectin and related compounds).
* Insecticide ear tags contain one or more insecticides embedded in a plastic matrix. They came out in the early 1980s and worked very well but after a few years horn flies started to develop a resistance. To maintain efficacy a couple steps should be followed, rotate the insecticide classes, do not use the same one year after year, withhold tagging until fly numbers reach 200 per animal, tag all adult cattle in the herd, use other methods of fly control, and last remove the fly tags in the fall.
What is the result if we don’t get it under control? The result may be decreased milk production, reduced weight gains, changes in grazing patterns and bunching of animals. Significant reduction in calf weaning weights is well documented. There are studies out of Nebraska that show weaning weights were 10-20 pounds higher when horn flies were controlled on cows. Horn flies can also be implicated in the spread of mastitis and this can also lead to blind quarters in replacement heifers.
Please contact Stacey Caughey, Interim Extension Educator for Stearns, Benton and Morrison counties with any questions at 218-330-5737 or butle269@umn.edu
— Stacey Caughey, Interim Extension Educator-Agriculture, University of Minnesota Extension, Stearns, Benton, & Morrison Counties
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