Friday, July 19, 2024
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Fly Management to Reduce Pinkeye Problems

It’s July, and as usual, the most popular article at On Pasture right now is “The Easiest Way to Treat Pink Eye.” Why July? Well, that’s when fly populations seem to reach their peak, and one fly in particular, the face fly, is a big part of spreading pink eye through a herd. That means a good way to reduce pink eye in our herd is to understand how these flies contribute to the problem, and what we can do to reduce their populations.

Know the Enemy

It’s hard to tell one fly from another just by looking at them, but their preferred home on a cow is a dead give away. Face flies get their name because they prefer a cow’s face, and in particular, its eyes. Why? A female fly feeds on the mucus and saliva around the eyes and nose to get the protein she needs for egg development. If there’s not enough she’ll poke around the eyes irritating them so they tear and give her what she’s looking for. As you’ve already guessed, this is a perfect way to spread pink eye. In fact, the bacteria that causes pink eye, Moraxella bovis, can survive up to 3 days on external surfaces and 2 days in the gut of face flies. That means one face fly can cause a lot of damage.

Once she’s gotten enough protein for her eggs, the face fly female lays her eggs in fresh manure. From egg to adult takes just 12 to 20 days, depending on the weather. Eggs hatch in one day, larvae develop in 2 to 4 days, and when mature, they leave the manure to pupate in the surrounding soil. Face flies winter over in buildings or other protected spaces spending their time in “diapause,” a kind of suspended or arrested development state.

Managing for Fewer Face Flies

According to the Merck Veterinary Manual:

“Control of face flies is difficult. Much effort has been made using various insecticides and application techniques, such as dust bags, mist sprays, and wipe-on formulations. Also, insecticides and insect growth regulators are used as feed additives. However, results are usually less than satisfactory. The introduction of insecticide-impregnated ear tags has provided somewhat better control, but generally, seasonal face fly reduction of only 70%–80% has been achieved, even with two tags (one in each ear) per animal.”

Other sources point out that fighting face flies with chemicals requires large dosages and chemicals are less and less effective as the flies become resistant to pesticides.

That leaves management as the best tool for reducing face fly populations. Here are some options:

1. Catch and Kill

New York Farmer Fred Forsburg built a better fly trap after watching fly behavior. He noticed that when his cattle dipped their heads into the water trough to drink, the flies lifted off and landed nearby to wait until it was safe to return. Fred realized that if he set up a board with fly paper near the trough, he’d be able to catch the flies. Since most of the flies on his cattle’s faces are female, he’d eliminate her and her potential progeny. It’s inexpensive, easy, and effective. Fred notes that he catches about 2,000 flies a day.

Here’s more from Fred on how you can set up your own face fly trap:

More Ways To Keep Flies Off Your Livestock

2. Minimize the Use of Pesticides and Worming Medications

Yellow dung flies, photo by James Lindsey Wikimedia Commons

Chemicals designed to kill flies also kill insects that are beneficial in reducing fly populations. By reducing the use of these insecticides, we have more dung beetles and dung beetles are helpful in removing manure patties so flies have fewer places to lay eggs and grow their young. You might also get help from Yellow Dung Flies. Male flies spend most of their time on manure piles, waiting for females and feeding on other insects like the flies that come to lay their own eggs. They help reduce fly populations, and their larvae eat manure as they grow.

3. Provide supplements

While different folks prescribe different supplements for keeping flies off cattle, the only one for which there is actual evidence is garlic. A study in Canada showed that trace mineral salt mixed with 2% garlic (by weight) reduced flies on cattle by about 50%. You can read more here:

Garlic for Fly Control?

4. Keep the Herd Moving

Moving herds to new pastures has been prescribed as another tool for keeping flies off cattle. The theory is that when the flies rise up mature out of the ground near their manure pat homes, the cows will already have moved on. The problem with this is that face flies are strong fliers, traveling as much as 5 miles to find the face of a cow. But this in combination with one or more of the other steps listed here is helpful to the overall problem.

Other Flies of Concern

If your cattle have flied on their backs and bellies, those are horn flies. These flies bite their host to obtain blood meals. They begin to reduce production at just 50 flies per side for dairy cows and 100 per side for beef cattle. These flies don’t like dark areas, so some farmers have built traps to capture the flies as they rise off the backs of cattle entering barns.

Like horn flies, stable flies bite and feed on blood. They are found on the legs of animals and just 10 to 15 per animal can cause production problems. To reduce them, you need to reduce the areas where they breed. Remove rotting organic materials near barns and sheds, calf hutches or bale feeders.

We’ve got more information coming up about dung beetles and insect predators to manage fly problems. In the meantime, if all this talk of flies brings you down, here’s something to cheer you up – Peter, Paul and Mary and a group of kids singing “There Was an Old Lady Who Swallowed a Fly.” Enjoy!

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Kathy Voth
Kathy Voth
I am the founder, editor and publisher of On Pasture, now retired. My career spanned 40 years of finding creative solutions to problems, and sharing ideas with people that encouraged them to work together and try new things. From figuring out how to teach livestock to eat weeds, to teaching range management to high schoolers, outdoor ed graduation camping trips with fifty 6th graders at a time, building firebreaks with a 130-goat herd, developing the signs and interpretation for the Storm King Fourteen Memorial trail, receiving the Conservation Service Award for my work building the 150-mile mountain bike trail from Grand Junction, Colorado to Moab, Utah...well, the list is long so I'll stop with, I've had a great time and I'm very grateful.


  1. I have had success using loose sulfur (available from my local Fertrell dealer) at a rate of 1lb per 50lb of kelp. Cheaper than garlic powder for sure.

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