Horn flies, ticks, and internal worms don’t care if it’s hot, dry, or the tail-end of summer. In fact, August is prime time for some of these pests to ramp up their damage—especially if your earlier control efforts are wearing off. That pour-on you applied in June? It may no longer be holding. And if your deworming strategy didn’t account for reinfection cycles, your herd could be quietly losing weight, milk production, and overall health. This reduction could translate to significant economic losses for your operation.
This season is the perfect time for a late-summer parasite check—a simple reassessment that could save you pounds, performance, and money come weaning. In this article, we’ll walk through how to evaluate if your herd is still protected, what warning signs to watch for, and the best options for correcting any gaps. Remember, early assessment can prevent performance loss, putting you in control of your herd’s health and productivity.
Don’t let parasites get the last word this season. Let’s make sure your herd finishes strong.
Parasites in August: Why They’re Still a Problem
When most producers think of parasite season, they think spring flush or early summer. But August still poses real risk, especially in warm, humid areas or places that get late-summer rain. Here’s why:
- Fly populations can spike again after a dip in mid-summer heat.
- Ticks remain active in brushy, shady areas or along creek beds.
- Internal parasites thrive when pastures are grazed down and cattle are forced to graze closer to manure.
Unlike a broken fence or a downed water line, parasites don’t announce themselves with drama. They rob performance quietly—lowering gains, dragging down body condition, and increasing stress that leaves your cattle more vulnerable to other issues.
Signs Your Cattle Might Be Losing the Parasite Battle
Even if they were treated earlier this summer, don’t assume you’re in the clear. Parasite resistance, reinfestation from untreated neighbors, or a product that wore off too soon can all open the door for trouble. This situation reiterates the need for vigilance and continuous monitoring even after initial treatment.
Watch for these signs:
- Increased fly pressure: More tail swishing, head shaking, or cattle bunched up mid-day.
- Weight loss or stalled gains: Especially in weaned calves or first-calf heifers.
- Dull coats and loose stool: Possible signs of internal parasites.
- Visible ticks, often around the ears, tailhead, or udder.
- Limping or swollen joints: Potential indicators of tick-borne disease.
Even one or two signs should prompt a closer look. Parasites rarely show up in isolation.
Horn Flies: Small Pest, Big Problem
If you’re seeing more flies buzzing around your cattle than usual—especially clustering on backs, shoulders, or around the midline—it might be time to do a horn fly check. Horn flies are tiny, but they pack a punch. These bloodsucking pests feed up to 40 times a day and rarely leave the animal, which means constant irritation and stress for your herd. You might notice cattle flicking their tails more often, bunching up, or standing in the wind trying to escape the pressure.
But the real problem isn’t just the nuisance—it’s the weight loss. Unchecked horn fly infestations can cost you up to 30 pounds of gain per calf over the course of the summer. That’s a big hit to your bottom line, especially when fly control options are relatively affordable and easy to apply. If it’s been over a month since your last fly treatment or your control method isn’t working as well as it used to, now’s the time to reassess and get ahead of the problem before it steals more performance.
How to spot them:
- Look for clusters of small black flies on the backs, shoulders, and sides.
- If you can count more than 200 per animal without squinting, it’s time to act.
Management options:
- Insecticide ear tags: Still useful if rotated yearly and applied correctly.
- Pour-ons or sprays: Offer quick knockdown but may not have long residual.
- Backrubbers/dust bags: Ideal for loafing areas, especially when combined with attractants like minerals or molasses.
- Feed-through larvicides: Can help reduce the next generation, but won’t control adult flies.
💡 Pro tip: Don’t rely on just one method. Rotating fly control strategies is key to staying ahead of resistance. Resistance refers to the ability of parasites to survive exposure to a particular control method. By rotating methods, you can prevent parasites from developing resistance and ensure the continued effectiveness of your control efforts.
Ticks: The Hidden Hitchhikers
Ticks often fly under the radar in summer parasite control, but ignoring them can be a costly mistake. Unlike horn flies that are easy to spot swarming backs and shoulders, ticks tend to hide out in the ears, under the tail, and in other hard-to-see places. But just because you don’t see them doesn’t mean they’re not doing damage. Ticks feed on blood, irritate cattle, and weaken their immune systems—especially in calves and stressed cows.
Beyond just being a nuisance, ticks can seriously impact your herd’s health and performance. They spread diseases like anaplasmosis, which can lead to hidden damage and reduced grazing time as cattle spend more energy scratching and swatting than eating. That’s a direct hit to weight gain and efficiency. August is a good time to check high-risk areas on your animals, especially if they’ve been in brushy pastures. If you find ticks, it may be time to rotate pour-ons, add back rubs, or consider other control options before fall hits.
August is prime time for:
- Lone star ticks
- Gulf Coast ticks
- American dog ticks
- Spinose ear ticks (especially in dry brushy areas)
What to do:
- Physical inspection is key. Check ears, neck, under the tail, and between the legs.
- Pour-on dewormers with added ectoparasite control (like ivermectin) can knock ticks down.
- Fly tags or tick collars may help in high-risk areas.
- Pasture management: Keep brush trimmed back and avoid forcing cattle into high-tick areas without protection.
Internal Parasites: The Invisible Performance Drain
You can’t see worms with your eyes, but you can see their impact if you know what to look for.
Late summer worm loads often rise due to:
- Overgrazed pastures
- Drier grass is forcing cattle to graze closer to the manure
- Calves picking up larvae while nosing around
- Prior dewormers are wearing off or underperforming due to resistance
Common culprits:
- Barber pole worm (Haemonchus contortus) – can cause anemia and death in severe cases.
- Brown stomach worm (Ostertagia) – decreases appetite and feed efficiency.
- Liver flukes – thrive in wet areas and swampy pastures.
Spotting trouble:
- Unthrifty appearance
- Poor weaning weights
- Bottle jaw (swelling under the jaw)
- Loose manure or dirty tails
If you’ve seen these signs—or want to be sure—you can run a fecal egg count (FEC) with your vet. It’s not overly expensive and can help you avoid wasting money on the wrong dewormer.
Treatment Timing: Is It Time to Deworm Again?
For many operations, a strategic fall deworming is already on the calendar. But August might call for an earlier move—especially if:
- Cattle look rough despite decent pasture
- You’re preparing calves for weaning
- You’ve had a wetter-than-usual summer
- You didn’t treat for parasites earlier in the year
Don’t just guess. A quick conversation with your vet or nutritionist can help fine-tune the timing. Merck has an excellent guide on creating a deworming schedule.
👉 Related Post: How To Really Control Summer Parasites Without Chemicals– this one dives deeper into natural and alternative options that might still be part of your program.
How to Prevent Reinfestation in Late Summer
Even if you get parasites under control, the key is keeping pressure low heading into fall. Here’s how:
- Keep minerals stocked—especially with fly-control options like IGR.
- Clean loafing areas to reduce breeding sites.
- Rotate pastures if possible, especially with cow/calf pairs.
- Control parasite hotspots, such as low spots, shade lines, or feeding areas.
- Treat the whole herd if one group is struggling. Spot-treating doesn’t help if they all share the same pasture.
And don’t forget to monitor performance—your cattle are the best gauge you’ve got. If they look and act healthy, that’s a good sign your parasite control is on track.
August Checklist: Quick Questions to Ask Yourself
Final Thoughts: Don’t Let Parasites Steal Your Gains
Parasites don’t always cause a dramatic crash—but they sure know how to chip away at your profits quietly. One missed dose, an expired tag, or a stretch of hot weather can be all it takes for flies, ticks, or internal worms to slip past your defenses. And when they do, they don’t just cause stress to your cattle—they slow down weight gain, drag down reproduction, and eat into your margins a little more each day.
That’s why August is the perfect time for a parasite reset. The worst of the summer heat might be behind us, but horn flies and ticks are still active, and internal parasite pressure often spikes as pastures get grazed down. So hit pause for a moment and ask yourself: “Is what I’m doing for parasite control still working?” If fly tags have lost their punch, dewormers aren’t holding like they used to, or cattle are showing signs of rubbing, tail flicking, or slower gains, now’s the time to reassess.
The good news? You don’t have to overhaul your entire plan—sometimes it’s just a matter of rotating products, reapplying what’s worn off, or adding a protein tub with fly control. Taking a few small steps now can save you from a full-blown mess in the fall. Your cattle—and your bottom line—will thank you.