Now’s the time for cattle producers to prevent winged pests from taking a bite out of profits. According to University of Missouri Extension regional livestock specialist Bill Doig, if you want to minimize fly problems in the heat of summer, it’s important to get control of them early. “Right now is definitely the peak time,” he said. “As we’re seeing all these weather systems come in, the flies are hatching and starting to take an effect on the animals.”
That means it’s time to apply a preventative measure, like a pour-on, spray or rub, before you turn cattle out onto new pasture; if you see a large number of flies in the field later in the season, he said, “you’re almost too late as far as getting the best effectiveness with your fly control.”
The horn fly is the most economically significant livestock pest of this region; thousands can take up residence on a single animal, and each one can take 10-12 blood meals a day. Other major pests include deerflies and horseflies in the pasture, and houseflies and stable flies in barns and other shelters. Doig said lack of control means lower profits.
“You’ll notice that the animals could potentially not be gaining as much weight; it just gives them more chance for infection of potential disease, if those flies have been exposed to it.
And it just kind of is a hassle to that animal; if that animal is worried more about keeping the flies off of their face, then they are not going to be out there trying to graze.”
Kelly Loftin, professor of entomology with University of Arkansas Extension, said it’s not uncommon for calf weaning weights to be reduced by 15 lbs due to excessive fly infestations, “and then if you look at some of the stocker cattle gain, it can be reduced by maybe 50 lbs.” He recommended farmers do a manual count of flies on cattle every week or two; you don’t have to be precise – unlike researchers, who take digital images of the animals for an exact count – but if counts exceed 150-200 flies per animal (100 for dairy cattle), that’s the threshold for treatment.
There are new tools available to producers who use ear tags for fly control. For many years, the only chemistries on the market were pyrethroids and organophosphates; “There was a tendency to overuse one or the other and not rotate insecticides, so people were starting to see resistance build up in the fly population,” Loftin said.
Three years ago, a new ear tag came out that contained an organochlorine insecticide, and later this year there will be a macrocyclic lactone, comparable to ivermectin. Loftin said the pyrethroids and organochlorines work more quickly, but he still advises farmers to use organophosphates in their rotation; if producers use the same tag continuously, he said, “in two to three years, you’re going to have a buildup in resistance where that tag doesn’t work any more.”
Whether producers use ear tags or other methods of fly control depends on their management strategies. “I know some farmers that actually still spray,” Loftin said. Other methods include the rubs, insecticide dust bags and sprays, which can be automated.
He said, “When fly populations reach a threshold they flip the switch, and the animal will be sprayed automatically as it goes in to get food.”
The problem with manual sprays, he said, and with pour-ons, is the added labor of getting the cattle up and through a chute. Another method is insect growth regulators (IGRs), which can be premixed with mineral or feed; the active ingredient is often methoprene or diflubenzuron, which mimic natural hormones that prevent immatures that are shed in the animal’s feces from developing into mature insects.
Loftin said some producers have used IGRs with success, but others have not, and there are management issues associated with them. “Are the animals consuming the correct amount? If it’s failing, they may not be eating enough. Another reason that method fails is, if you’ve got a herd of cattle that are treated with this IGR surrounded by cattle in adjacent pastures that aren’t treated, there’ll be some immigration from untreated herds.”
Adult horn flies are not affected by the growth regulator, so they’ll just continue to feed on the treated cattle. Doig chimed in with a couple of additional control methods. For operations that involve shelters, particularly nearer to town, glue traps and strips can be an effective and inexpensive way of dealing with indoor pests. And natural control can be achieved with parasitic wasps, tiny creatures that infest the flies themselves.
Doig said, “That method can be a little more expensive. than basically what your typical methods have been. But it’s a new way of looking at it; it’s a new way of trying to control them, and I would encourage at least people to look at that as something that might be an option for them.”
