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The horn fly is one of the most damaging external parasites of cattle in Nebraska, causing reduced weight gain and milk production once numbers exceed 200 flies per animal. In northeast Nebraska, fly emergence typically begins in late May and continues into fall. Now is the time to evaluate your fly control management for the upcoming grazing season. Was control adequate in 2024? If not, consider changing products or methods. Extension Entomologist Dave Boxler outlines several control options: Pour-ons Applied along the back, these insecticides provide control for several weeks but require reapplication throughout the fly season.
Animal Sprays Sprays o#er 714 days of control, so again regular reapplication will be needed. Low- and high-pressure sprayers require cattle to be corralled for adequate coverage. Mist blower applications in pasture reduce stress compared to corralling cattle.
Oral Larvicides (IGRs) Mixed into mineral or feed, these prevent larvae from maturing in manure. Begin 30 days before fly season for good control. The catch: they don't kill adult flies.
Insecticide Ear Tags Apply late May to early June. Be sure to read the label and use the correct number of tags per animal for season-long protection. If applied to early, e#ectiveness declines while fly numbers are still high. Tagging only the calf or cow, not both will not provide the desired level of control.
Compressed Air (Vet Gun) VetCaps deliver insecticide from a distance using compressed air and provide 1035 days of control. Use on cattle 600 lbs and over.
Garlic Mixed into salt or mianeral at 2%. Research results are mixed-some show reductions, others no e#ect, so use at your discretion. UNL studies in Nebraska have shown no e#ect.
Dust Bags, Backrubbers, Oilers Best used in a "forced-use" setup (e.g., near water) where animals have to be treated. One location can treat 50-60 cows. Oilers should use No. 2 diesel fuel or mineral oil and be recharged weekly. Do not use motor oil.
Traps (e.g., Bruce Trap) Physically remove flies as cattle walk through. Field studies show up to 41% fly reduction with repeated use.
Always remember to follow all withdrawal periods before marketing animals. Be aware that flies from neighboring herds can repopulate treated animals, masking the e#ectiveness of your control measures. Finally, rotate insecticides to avoid resistance-many horn fly populations in Nebraska are showing resistance to pyrethroids.
E#ective fly control is critical for a productive and healthy herd. Consider your options and pick one that meets your operational goals and is e#ective to ensure a fly free summer for your animals.
—Ben Beckman is a beef systems Extension Educator serving northeast Nebraska. He is based out of the Cedar County Extension oce in Hartington. You can reach him by phone: (402) 254-6821 or email: [email protected]
