Grazing season is just around the corner. As you prepare pastures by fertilizing, spraying, burning and interseeding—also prepare cattle for spring by controlling parasites early.

Flies and worms can lower cattle health, which can lead to major economic damage, so controlling them with insecticides and other management protocols is important.

“The biggest thing on fly control is how it matches up with your management program,” explains Justin Talley, entomologist with Oklahoma State University.

Fly control measures are often implemented when doing other cattle work, such as pregnancy checks, weaning or branding. Prior to turnout on pasture for the spring-summer grazing season is a prime time to plan for fly control, too.

Horn flies, found nationwide, are the primary external parasite that causes problems for cattlemen.

In the Southern Plains horn flies can start to show up in heavy numbers by April, depending on the weather, and stay until October. “Not only are horn flies a significant pest, they are a long-season parasite compared to other flies,” Talley explains. “Growing cattle gain an extra 1.5 lb. per week when horn flies are controlled.”

Weaning weights can increase 12 lb. to 15 lb. for calves nursing cows that have had fly control, adds Larry Hawkins, Bayer Animal Health senior technical services veterinarian. It can amount to quite a few dollars added to the bottom line.

“Most fly control doesn’t cost half of the gains seen in weight, so I think it is worthwhile,” Hawkins says. Fly tags are a good place to start with fly control because they are simple to use. A producer can tag their calves or cows prior to sending them out to grass in the spring and get several months of fly control.

Talley would like to see producers tagging in mid-May or even June to get the best use out of the tag later in the grazing season. Hawkins recommends tagging cattle when 50 to 100 flies are present per animal.

The only problem is tagging might not coincide with when producers are doing other chute-side processes or when field work or haying requires their attention. Cattlemen might need to put tags in earlier, which means they will wear off before the peak fly season.

July and August are the critical months for horn flies. Unfortunately, those hot summer months are not when people typically work cattle, making it difficult to implement some fly control protocols.

If fly tags do lose potency in the late summer there are plenty of options:

  • Oilers or dusters can be used during peak season. They need to be located at mineral sites or water tanks where a producer is sure every animal will walk underneath the oiler or duster for fly protection. “I usually advocate this for producers who are moving cattle in a rotational system,” Talley says.
  • Spraying cattle periodically while out on pasture is a possibility for some producers. It requires proper spraying equipment, but can be effective when performed every few weeks. Talley says you need to pay attention to the weather so the product won’t be impacted by a significant rain event. Always follow the label requirements.
  • A pour-on fly treatment can be used on cattle that are close to a processing facility and can be run through the chute. “At most you’ll get three months of adequate use,” Talley says. Keep in mind the economic threshold for a second treatment is 200 to 300 flies. 
  • Feed-through products, such as an insect growth regulator (IGR) can be added to mineral during the grazing season.

“The biggest benefit with using IGR feed-through is it controls the immature stage,” Talley says.

The IGR product is consumed from mineral, passed through the animal and deposited in the manure. The IGR prevents the eggs from growing to term.

One downside of the IGR method is if your neighbors aren’t executing similar control methods—there will still be adult flies coming over to bother cattle on your pastures.

“You certainly need to have some treatment on those cattle, such as an ear tag to control adult flies coming from the neighbor,” Talley says.

Still, Hawkins says feed-through IGR products are good at controlling local fly populations. “If you can kill the homegrown flies in a manure pat before they become adults you’re dollars ahead,” Hawkins says.

Horn flies aren’t the only flies cattlemen need to worry about. Stable flies and horseflies also cause irritation to cattle. 

Stable flies are generally present on the legs of cattle. The best prevention is to clean up winter feeding sites such as the area surrounding a hay ring or bunk feeders.

“We see stable flies earlier in the season than horn flies. If you get your spilled hay cleaned up you’re doing a lot to disrupt that stable fly life cycle,” Talley says.

Horseflies are some of the toughest parasites to control because only the females feed and they only do it for short periods of time.

“Even if you just put product on the animal to control horseflies you aren’t really making a dent in the population,” Talley says. 

The larval stage for horseflies usually develops in semiaquatic areas, making it difficult to prevent their growth. Many other flies develop in manure or spoiled feed.

Horseflies are important to control, however, because they are responsible for the transmission of anaplasmosis.

“You want to try and repel horseflies and a pyrethroid can somewhat do that,” Talley says. Spraying every few weeks when horseflies are prevalent is an option, as well as using fly traps.

Early in the grazing season worm control and fly control can go hand-in-hand depending on health programs.

Pour-on dewormers like endectocides are an option to treat cattle for both internal and external parasites.

“My biggest concern with an endectocides is what are you doing with your worm load? Those are the parasites that are unseen, but cause a lot of problems,” Talley says.

There have been cases where worms have become resistant to a class of dewormer because producers were using a pour-on dewormer as a fly control method.

“Ideally we want to avoid using endectocides just for fly control. They are just an added benefit for getting a bit of early season fly control when controlling worms,” Talley says.

Producers know there are several benefits to deworming cattle, says Tony Moravec, veterinarian with Merial Animal Health.

Getting rid of internal parasites helps with immunity, which leads to improved feed consumption and conversion. Because of cattle’s improved immunity, vaccinations overall should work better. Worms are found across much of the country, particularly in high moisture areas. If there are worms present, Moravec says cattle are reinfecting themselves with every bite of grass they eat.

“The focus is treating our cattle, the problem is only 10% of the worm population are in the cattle,” Moravec says. The other 90% are found in the pasture. 

This means the efforts need be on what is happening outside of the cow, along with inside.

“If you can keep your cows clean that will impact the environment around you,” Moravec says.

Dormant worms in the abomasum and overwintering juvenile worms in the ground emerge when conditions are just right.

Moravec recommends treating cows and calves with a dewormer in the spring prior to pasture turnout to help keep the worm infestations down. A long-acting, injectable dewormer is an option to control worms for a longer period of time and cover an entire grazing season. When cows have improved immunity and feed efficiency, this also benefits the calf at her side and the embryo developing internally, Moravec notes.

“Deworming a cow is the best bang for your buck,” Moravec says.

There are many ways to approach fly and worm control this spring. Choose the methods that work best for your management system.