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Herd Health & Disease Management

Fly Control on Dairy Farms

Flies bother cows, spread disease and annoy neighbors. The best control begins with removing the places they breed, and then adds other tools only as needed.

Key points

  • Remove moist breeding sites first, since that does the most.
  • Keep barns, calf areas and manure piles clean and dry.
  • Use traps and other non-chemical tools where they help.
  • Use only products labeled for dairy cattle and follow the label exactly.
  • Keep records and ask your extension office or vet for advice.

Why flies matter

Flies irritate cows, which then eat less, lie less and make less milk. Some species bite and cause painful sores. Flies can also carry disease-causing organisms from manure to teats and calf feed.

Complaints from neighbors can also follow a fly problem. Good fly control protects cow comfort, herd health and farm relations.

Start with breeding sites

Flies need moist organic matter to breed. Wet bedding, spilled feed, manure piles, calf hutch bedding and leaking waterers are common sites. Cutting off these sites does more than any spray.

Walk the farm and look at corners, drains and the back of buildings. Where you see wet material, fix the cause.

Barn and housing practices

Good ventilation and clean, dry resting areas keep flies down. Keep gutters, alleys and under-feeder areas clean. Space manure piles away from the barn and calf areas, and think about the wind direction.

Calf areas need special attention because wet bedding stays warm and young calves are hit hard by biting flies.

Trapping and non-chemical tools

Traps, sticky tapes and baited stations can lower adult numbers when used alongside cleanup. Place them where flies gather, away from feed and milk areas, and follow manufacturer directions. Some farms use biological controls such as natural predators of fly pupae. Ask your extension office what works in your area.

Check and replace traps regularly, since a full trap does little.

Insecticides and product safety

Insecticides and animal treatments are tools of last resort in a good program, not the first step. Use only products labeled for dairy cattle and for the intended use, and follow the label exactly. Labels set rules for animal use, milk and slaughter, handling and storage.

Do not guess at mixing or rates and do not use products intended for other animals or crops. Talk to your veterinarian, extension specialist or licensed applicator before choosing a product, and follow milk buyer and certification program rules. Insecticides can harm people, bees and the environment, so wear protective gear and keep records.

Resistance and rotating strategies

Flies can develop resistance to products that are overused. Rotating methods and relying on sanitation reduces that risk. Your extension office or an applicator can advise on rotation plans that suit your farm.

Watch for the places where a product no longer seems to work and report that to your advisor.

Common mistakes

Spraying without cleaning up breeding sites, using products against label directions, overlooking calf areas and manure piles and failing to keep records are common. Another is putting traps in the wrong place. Follow label and vet-set withdrawal times for milk and meat, and keep treated-animal rules in mind.

When to get help: Contact your extension office or a licensed applicator for help choosing products and planning rotation. Call your veterinarian if cows show sores, heavy irritation or sudden milk drop. Follow all label, milk buyer and certification program rules.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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