Those old-time Chinese warriors had some pretty sage wisdom — know your enemy. To that, modern combatants in the annual Fly Wars add that it's a good idea to know your weapons, as well.
So, as you're girding your loins for another battle with the winged enemy that torments cattle and drains profits in pastures nationwide, consider the species you will face and the options you have for control.
First, the flies
There are a variety of flies that use cattle as a host — horn flies, stable flies, face flies, and horse and deer flies. The two of greatest interest are horn flies and stable flies. And of these, the only one you can really do anything about is horn flies.
Horn flies are those bugs that stay on cattle all the time, usually bunched up in a mass along the withers and down the back to the tailhead. In the heat of the summer sun, horn flies will also mass on the shady underside of the animal. These flies will only leave the animal to fly down to a fresh cow patty and lay eggs. However, before they find an animal host, they can travel quite a distance, meaning you and your neighbors can swap flies throughout the fly season.
Stable flies, on the other hand, congregate on the legs. Unlike horn flies, stable flies will only land on an animal when seeking a blood meal. Once satiated, they fly off to complete their life cycle. Horse and deer flies are similar, dive-bombing an animal, taking a blood meal, then leaving. Face flies, which are more of a problem in the upper Midwest and Northeast, feed on the secretions from the eye and nose.
Control
Now that you know your enemy, or at least know where to find it on the animal, you can choose your weapons. Trouble is, the armament available today only works with any prolonged effectiveness on horn flies.
That's because horn flies are the only ones that hang around long enough for the insecticide to do any good. The other types of flies don't stay in contact with the animal long enough for any current control method to be effective.
“I don't try to encourage much optimism in being able to control face flies,” says Roger Moon, a University of Minnesota veterinary entomologist. The same holds true for horse flies and stable flies.
However, all is not completely lost, at least with stable flies. While chemical control doesn't work, there are some management options that can be effective.
According to Justin Talley, Oklahoma State University Extension livestock entomologist, stable flies used to be considered a problem only in confinement situations, such as feedyards, dairies or swine operations. But as cattlemen adopted round bales for winter feed, the stable fly took advantage of the situation and prospered.
The hay residue left from round bales, combined with manure from the cattle, makes ideal habitat for the fly larvae.
“And they're really productive sites,” Moon says. “You can find dozens of maggots in an area the size of a teacup. And if you're is feeding multiple rings, all those places are producing a wave of stable flies late spring and into summer.”
Talley's research shows several ways cattlemen can make life much more inhospitable for stable flies and their larvae. The first is to unroll the round bale when you're feeding, rather than put it inside a hay ring and let the cattle feed free-choice. This spreads out the cattle, which spreads out the residue and the manure.
However, proving there are no perfect trade-offs, feeding off the ground can encourage the spread of internal parasites such as the brown stomach worm. Rotating your feed grounds, just as moving hay rings to keep stable flies off balance, can help.
The second, if using hay rings makes more sense in your management system, is to clean up the feed grounds before fly season. “Disturb the habitat in some way,” Talley suggests. “Even if you go in there and scrape through it or scrape it into a pile, it will help.” Moon suggests, in addition to that, consider moving your hay rings between bales as you're feeding in the winter. That way, you don't get an accumulation of residue from multiple bales.
It's worth the effort, Talley says, because reducing the number of stable flies will help your cattle tolerate their existence.
“Research shows that 72% of the weight loss from stable flies is caused by the animal's behavior — bunching — and 28% of weight loss is attributed to the stable fly feeding.”
Good housekeeping won't completely cure your stable fly problem, because they move around quite a bit. So if you have neighbors who don't clean up their feed grounds, or you live in an area where suburban encroachment is a problem, stable flies, like face flies, may simply be a pest you just have to live with.
Horn flies
That leaves us with horn flies. Traditionally, and yet today, the main ways to control horn flies are with ear tags, pour-ons, and oilers or dust bags in the pasture.
Insecticidal ear tags came out more than 25 years ago and are still among the top choices for horn-fly control, says Phil Kaufman, University of Florida veterinary entomologist. “When they [ear tags] first came out, they killed everything and they'd last all summer long. Well, it only took horn flies in some parts of the country a couple of years to develop resistance. So we need to be a little smarter about this.”
Which means, the experts agree, only use ear tags, and pour-ons for that matter, when you need them. While that's good advice, the problem is that the life cycle of the fly doesn't coincide very well with the work cycle of a cattleman.
“Say you're in Tennessee and horn flies don't really show up there until April or May, but you worked your cattle back in February,” Kaufman says. “You really need to bring those animals in again and put the insecticide ear tags in April or May when the horn flies become a problem. Not everybody wants to do that.”
So you apply the tags or the pour-on when it's convenient for you. “You're basically putting on this product and it's doing you absolutely no good,” says Bert Stromberg, University of Minnesota professor of parasitology. While there's a cost associated with working your cattle a couple of extra times to apply fly control, there's also a cost associated with using the products incorrectly, not to mention what you're doing to encourage insecticide-resistant flies.
“You might as well keep it in the can and use it for another day,” Stromberg says.
That “other day” will vary by region, of course, but you can gauge when you need to start fly control by watching your cattle. The general threshold is 200 flies/animal. Take a look at 10 or 12 animals and if it looks like they're harboring more than that, get to work.
But just as applying the tag too early can foster resistant flies, leaving the tag in too long has the same effect. You want to pull the tags as soon as possible after fly season or if you notice populations beginning to increase.
“Ear tags release the insecticide at an effective level for quite a while, but then the level drops off fairly quickly,” Kaufman says. “It's when you are in that drop-off period that you are allowing for more of those partially resistant individuals to survive.”
Since cattle on summer pasture often aren't easy to gather and treat, there are a couple of additional options.
“The most primitive, but still effective, is back rubbers and dust bags charged with some sort of topical insecticide, usually pyrethroids, although organophosphates are still used,” Moon says.
Fence off an area where cattle come and go, like a water tank or mineral feeder, and make an entryway. Hang a dust bag or oiler in such a way that the cows are forced to contact it as they walk in and out.
“That ensures pretty good coverage of the herd,” Moon says. “If you just hang an oiler out under a tree, a few of the animals will come play with it every once in a while, but you won't get anywhere near the coverage that is required to get effective horn fly control.”
Another option is feed-through products added to the mineral. These products target horn-fly reproduction by inhibiting the growth of the larvae as it develops in the fresh manure. While these products can be effective in killing the larvae, they don't kill the adult flies. So if your cattle are close to a neighbor who isn't using fly control, you may continue to see adult flies. While it's best to wait until flies become a problem to use topical control like ear tags or pour-ons, start using the feed-through product before flies appear to ensure it starts controlling flies early in the season.
Typically, Moon says, flies pose the greatest problem during the second half of the grazing season. “If you control horn flies well with any kind of insecticide, they sooner than later develop a resistance to the products.”
That process can be slowed by rotating products and using them according to label directions and only when fly populations dictate. “Letting the flies go uncontrolled for a while (early in the grazing season) slows down the development of resistance,” he adds.
Know your enemy and pick your weapon. But remember, fire only when necessary, and then aim to kill.
