Gaining Ground: Managing On-Farm Fly Populations


The persistent buzz and tickle of tiny feet on my face early this morning as the sun rose reminded me that fly season has reached our part of the country once again. Hopefully, most of you will have started your fly management activities months ago, but for those a little slow off the bat, or everyone looking for extra tips and information, let’s look at where to prioritize your investments of time and money.

Clean and Dry!

This has been said and written so often, it’s practically a cliché. But there are still some farmers spending precious time and money seeking magic bullet solutions while ignoring the fundamental fact that flies require moist organic matter in order to reproduce and multiply: the less habitat available, the lower the fly population.

Of course, it is practically impossible to eliminate all possible breeding areas, but targeting expenditures on this area will provide the greatest return on investment, especially over the long term. Generally speaking, farmers who report success using other control methods are those who have first invested in keeping the environment as clean and dry as possible.

  • Clean up spilled feed and rotting piles of waste hay or bedding
  • Mow vegetation around the barn to reduce resting and breeding areas
  • Clean out box stalls and bedding packs well in advance of fly season (spreading this manure or windrowing it in a field away from the barn will help further, as will spreading lime in the empty stalls)
  • Relocate and clean dairy calf hutches onto a smooth, level surface
  • Empty manure pits and spreading stacker piles in the spring
  • Grade barnyards and corrals for proper drainage
  • Keep livestock clean and dry: flies are attracted to dirty, sweaty animals
  • Provide good air flow, a cow brush, shade; trim long tails
  • Consider dusting cows with field-grade limestone (adds calcium to your pastures, too!)

Environmental Modification

Obviously, keeping things clean and dry is the primary environmental modification, but other measures can make the farm less attractive or less conducive to fly populations.

  • Sprinkle hydrated lime in wet areas will kill fly larva
  • Lime, rock phosphate, or diatomaceous earth in bedding can alter the pH and help keep things drier; anecdotal reports suggest that rock phosphate reduces the odours which attract flies to manure; switching away from straw as bedding can also reduce fly populations
  • Include some dry hay in the ration (or “grazing tall”) can reduce protein levels in the manure; farmers observe that this makes the manure less attractive to flies, and firmer manure obviously makes it easier to keep everything cleaner
  • Increase air flow in the barn and/or around calf housing makes the environment less friendly to flies
  • Turn or disturb manure/compost piles to interrupt the larval stage of development (this usually takes 7 to 10 days for house flies, and up to 21 days for stable flies)
  • Harrow pastures to spread and dry out manure pats (especially important for horn fly control, as they only lay eggs in manure less than 10 minutes old)
  • Rotating pastures to keep cows away from old manure pats which are hatching new flies

Direct Attack

Once you’ve done everything possible to keep flies from breeding and loitering in the barn and pastures, it’s time to go after the remaining (and hopefully much reduced) population. Predators, traps, repellents, and killing sprays are all options.

  • Predators can include poultry like chickens and ducks (Muscovy ducks are the breed of choice); in addition to eating flies and larva, they will also break apart and spread out manure pats on pastures (if you’re a dairy farmer, just be sure not to run “a-fowl” of your milk inspector!).
  • Parasitic wasps are tiny predators that attack fly larva. Start using them early in the year (April) to build up their populations in advance of the flies. Experience indicates that they perform best in relatively confined areas like calf-raising areas, and their effectiveness increases over the first few years of use – don’t give up after just one year.
  • Traps vary depending on the type of fly you want to control. Sticky traps (paper or tapes) in the barn offer one of the most popular methods of fly control. Research conducted by the Alfred Campus of University of Guelph demonstrated that the sticky roll offered the most cost effective method of controlling flies in the barn. For best results, farmers suggest stringing the tape above the pipeline (often the warmest spot in the barn and therefore where flies will congregate), and replacing it with a fresh length often – as often as once or even twice a day during peak fly season and in dusty conditions.

Variety of Traps

Attractant traps utilizing a scented liquid and some type of bottle or bag are effective at trapping house flies, but not other species. The “Epps” and “Horse Pal” traps are designed to trap stable, house, deer, and horse flies by mimicking the size and shape of an animal: these traps are effective, but they are also relatively expensive and require routine maintenance. Alsynite traps are cylinders of clear fiberglass covered in a clear sticky paper that refract light in a way that is attractive to stable flies; they are cheap and easy to install and move but require regular monitoring to replace the sticky paper.

Walk-through traps are the only mechanical option for the control of horn flies. They have been shown to reduce horn fly populations by 40 to 70% over time, and although the initial investment is high, they are durable, moveable, and reusable. Detailed plans for one can be found on the University of Missouri website at for those interested in building their own.

  • Repellents are becoming more popular. Some farmers report that using Ecoscent (formerly Ecophyte) in a backpack sprayer is effective at ridding cows, heifers, and calves of flies in the barn. In the summer of 2012, the Alfred Campus did an experiment that showed significant benefits (fewer flies, less defensive behaviour, more grazing, less walking) using a mixture of essential oils of lemongrass and geranium as a repellent while the cows were on pasture. (A 50/50 mixture of the essential oils was sprayed on the cows at a 5% concentration).
  • Sprays can offer “mechanical” control. Dairy farmers report that spraying the cows with soy or mineral oil as they enter the barn will knock down flies. In addition to synthetic fly sprays, there are also natural insecticidal sprays commercially available. One farmer reported very good results with “Safer’s End All II” concentrate (at a 2% concentration), cautioning that the product had to contact the flies directly, and that it was used later in the season, in conjunction with good sanitation and parasitic wasps. This product is a mix of natural pyrethrins and insecticidal soap. “Pyganic” is another pyrethrin-based product that is approved for organic use. Before resorting to these sprays, keep in mind that they are broad-spectrum sprays – resistance and impact on non-target insects (like mature parasitic wasps) must be considered (organic farmers must also seek approval from their certification bodies).
  • Clever applications. One producer has even purchased a battery-operated paint sprayer that he can carry to the pasture to spray his dry cows and heifers. The recommended model is the “Graco Truecoat Plus Cordless Sprayer” because it looks like a cordless drill with an added paint can and runs off the same type of 18V rechargeable battery.

Flies are not a “Fact of Life”

High fly populations and the stress and annoyance they cause to humans and livestock alike don’t need to be accepted as a “fact of life” during summer on farms. Good management and a multi-pronged approach can make a big difference – a difference that will show up in happier people and happier, more productive animals!

Essential oil repellent used by researchers at the Alfred Campus organic dairy research centre:

  • 25 ml lemongrass essential oil
  • 25 ml geranium essential oil
  • 950 ml sunflower oil

This will make enough spray to cover about 10 cows (Alfred used 120ml/cow). The sunflower oil could be replaced with either soybean oil or white mineral oil.

Essential oils can be purchased at health food stores or online. A list of Ontario-based companies selling wholesale essential oils can be found at

Producers have noted that mineral oil tends to collect less dust and dirt than soybean oil, leaving the cows cleaner and perhaps cooler.

Wake up with RealAgriculture

Subscribe to our daily newsletters to keep you up-to-date with our latest coverage every morning.

Wake up with RealAgriculture

Please register to read and comment.


Register for a RealAgriculture account to manage your Shortcut menu instead of the default.