Why Fly Control Matters
Flies are more than a nuisance , they cost you money. Horn flies alone cause an estimated $1 billion in annual losses to the US cattle industry through reduced weight gain, lower milk production, and decreased feed efficiency.
A horn fly population of 200+ per animal can reduce weight gains by 10-15% in calves and decrease milk production in cows. That's real money walking away every day you don't control them.
Know Your Flies
Horn Flies
The most economically damaging fly for cattle. Small (half the size of a house fly), dark-colored, and they bite. They feed on blood , 10-40 times per day per fly. They cluster on the back, shoulders, and sides of cattle.
Identification: Small, dark, and they bite. Cattle bunch together,甩 their tails, and rub against objects when horn fly pressure is high.
Face Flies
Larger than horn flies, they feed on secretions around the eyes, nose, and mouth. They don't bite but cause irritation and can transmit pinkeye-causing bacteria.
Stable Flies
Look like house flies but bite. They feed on blood from the legs and lower body. Severe infestations cause cattle to bunch, stomp, and reduce grazing time. Stable flies develop in decaying organic matter , old hay, manure, and wet bedding.
House Flies
The common house fly doesn't bite cattle, but they're annoying and can transmit disease. They breed in fresh manure.
Prevention: Reduce Breeding Sites
The best fly control starts with eliminating breeding habitat:
- Manure management: Spread or compost manure regularly. Horn flies breed in fresh cow pats , spreading manure breaks the breeding cycle.
- Remove old feed: Decaying hay, silage, and feed waste are breeding grounds for stable flies. Clean up around feed bunks and hay rings.
- Rotational grazing: Moving cattle frequently reduces manure concentration in any one area.
- Shade management: Fly populations concentrate under shade structures. Rotate shade areas or clean them regularly.
Treatment Options
Pour-On Insecticides
Applied to the back of the animal, pour-ons are the most common treatment. Products containing cyfluthrin, permethrin, or doramectin provide 2-4 weeks of control. Easy to apply, but can be affected by rain shortly after application.
Ear Tags
Insecticide-impregnated ear tags release chemicals slowly over 3-5 months. Effective for horn flies and face flies. The downside: resistance develops quickly if you use the same chemical class every year. Rotate tag chemistry annually.
Feed-Through Products
Insect growth regulators (IGRs) like cyromazine and diflubenzuron are fed to cattle and pass through into the manure. They prevent fly larvae from developing in the manure. Effective for horn flies, but doesn't kill adult flies already on the animal.
Sprays and Backrubbers
Hand sprays, spray-rubs, and oiler/backrubber devices provide contact insecticide to cattle as they use them. Good for operations where individual treatment is impractical.
Biological Control
Parasitic wasps (e.g., Spalangia spp.) lay their eggs in fly pupae, killing the developing flies. This works best as part of an integrated program, not as a standalone solution.
Integrated Fly Control: The Best Approach
No single method works best alone. The most effective programs combine multiple approaches:
- Reduce breeding habitat (manure management, clean feed areas)
- Treat cattle (pour-on, tag, or feed-through)
- Use biological control (parasitic wasps in confined areas)
- Monitor populations (count flies regularly to know when treatment is needed)
When to Treat
The economic threshold for horn flies is about 200 per animal. Below that, the cost of treatment may exceed the economic damage. Above that, treatment pays for itself.
How to count: Walk through the herd and count flies on 10-15 animals. Average the count. If the average is 200+, treat. Count at least once a week during fly season.
Managing Insecticide Resistance
Fly populations develop resistance to insecticides over time. To slow resistance:
- Rotate chemical classes every year. If you used a pyrethroid tag this year, use an organophosphate next year.
- Use refugia. Leave 10-20% of the herd untreated. This maintains a population of susceptible flies that dilute resistant genes.
- Combine methods. Using multiple control methods reduces selection pressure on any one chemical.
- Treat only when needed. Don't treat prophylactically if fly populations are below threshold.
Seasonal Fly Control Calendar
| Month | Action |
|---|---|
| March | Clean up winter manure buildup, remove old feed, prepare fly control supplies |
| April | Install ear tags or start feed-through products. Begin weekly fly counts. |
| May-June | Peak fly pressure begins. Apply pour-on treatments as needed. Release parasitic wasps in confined areas. |
| July-August | Peak season. Monitor weekly. Treat when counts exceed 200 horn flies. Clean up manure around water and shade areas. |
| September | Begin removing ear tags. Fly pressure declining. Continue monitoring. |
| October-November | Fly season ends. Final manure cleanup. Plan next year's program. Rotate chemical classes. |
Fly Control by Species
Beef Cattle on Pasture
Beef cattle on pasture face the highest horn fly pressure. Pour-ons, ear tags, and feed-through products are the primary tools. Rotational grazing helps reduce breeding sites. Start treatment before fly season begins.
Dairy Cattle
Dairy cows face additional stable fly pressure due to barn environments. Focus on manure management in barns, use fly traps, and maintain clean bedding. Avoid chemical residues near milking areas.
Calves
Calves are more susceptible to fly irritation than adults. Use calf-friendly ear tags or fly bags near calf hutches. Keep bedding clean and dry.
Product Comparison Table
| Method | Target Flies | Duration | Pros | Cons |
|---|---|---|---|---|
| Pour-On | Horn, face, stable | 2-4 weeks | Easy to apply | Rain affected |
| Ear Tags | Horn, face | 3-5 months | Long-lasting | Resistance develops |
| Feed-Through (IGR) | Horn (larvae) | Continuous | Prevents larvae | Doesn't kill adults |
| Sprays | All species | 1-2 weeks | Targeted | Labor intensive |
| Biological (Wasps) | Horn (larvae) | Ongoing | Natural, no chemicals | Slow acting |
Track Fly Pressure
Recording fly counts, treatment dates, and products used helps you build a year-over-year record of fly pressure and control effectiveness. Over time, you'll see patterns , which pastures have the worst fly problems, which products work best, and when fly season peaks.
QualityHerd lets you log pest control events and track treatment effectiveness. This data helps you optimize your fly control program and reduce costs.
Get Ahead of Fly Season
Fly control is easier to prevent than to treat. Start your program before fly populations explode , clean up breeding habitat, install ear tags or start feed-through products early, and monitor regularly. It's much easier to keep fly populations low than to bring them down after they're out of control.
Frequently Asked Questions
What is the best way to control flies on cattle?
The best fly control combines multiple methods: eliminate breeding sites by spreading manure and cleaning up old feed, use pour-on insecticides, ear tags, or feed-through products, deploy parasitic wasps for biological control, and monitor fly populations weekly to treat only when needed (200+ horn flies per animal).
How to keep flies off cattle naturally?
Natural methods include rotational grazing to spread manure, installing fans in barns, using fly traps (bag traps, sticky traps), deploying parasitic wasps (Spalangia spp.), planting fly-repelling plants near holding areas, and maintaining clean water troughs and feed areas.
What time of year do flies become a problem?
Fly season runs April through October in most of the US, peaking June-August when temperatures are warmest. Start your fly control program in March/April before populations explode.
How much weight loss do flies cause?
Horn flies at 200+ per animal reduce weight gains by 10-15% in calves and decrease milk production by 1-2 lbs/day in cows. For a 500-lb calf gaining 2 lbs/day, that's $50-100 per head at weaning.
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