The Horn Fly Threat: How to Identify, Control, and Prevent Infestations

The Horn Fly Threat: How to Identify, Control, and Prevent Infestations

Article and photo courtesy of Central Life Sciences

Did you know that the horn fly is one of the most economically damaging pests of pasture cattle in the United States? Horn flies cost cattle producers approximately $1 billion every year. But how can you fix this problem if you don’t even know what to look for?

Horn flies are the most prevalent and costly external parasites of cattle in North America. The stress caused by horn flies can result in interrupted grazing patterns, leading to impacted milk production and reduced weight gains in cattle. Implementing a horn fly management program with your cattle will help promote overall herd health.

To better help you identify and control horn fly infestations on your operation, Central Life Sciences is here to help keep your cattle comfortable and your profits high.

What is a Horn Fly?

Horn flies are small biting flies with piercing-type mouthparts, which take up to 40 blood meals per day. They are grayish with two stripes on their thorax and are usually found congregating on the backs and sides of cattle.

Horn flies typically only leave the backs of cattle to lay their eggs in fresh manure. These eggs hatch and develop into larvae in the manure and pupate underneath or in the surrounding soil around the manure. After the pupae molt, the adult horn flies emerge to reproduce and feed for up to 4 weeks. While the total life span of horn flies is slightly longer than one month, their populations build quickly, causing explosive infestations in the warmer months.

Signs of Horn Fly Infestations

  • Flies on the backs of cattle
  • Twitching
  • Tail swishing

The economic threshold for horn flies is 200 per cow or 100 per side. When left untreated, fly infestations can rapidly increase to thousands of flies per animal, leading to increased cattle stress that impacts performance. This causes cattle to burn excess energy to combat the flies, reducing grazing time, feed intake and daily gain. These stress behaviors impact weight gain, decreases milk production, milk quality and reproductivity such as conception and breed back timing. 

Disease from Horn Flies

Horn flies can also impact cattle health by spreading disease. Horn flies constantly are feeding from the cattle, allowing them to easily transfer disease agents. Horn flies are implicated in transferring heifer mastitis. As they feed on the teats and udders, they are able to transmit the bacteria. The bacteria enter the teat and moves through the quarter, destroying milk-producing tissues. If left untreated, heifer mastitis can affect the heifers’ milk production and life-long productivity before she has her first calf.

How Can Altosid® IGR Help?

Given the role horn flies play in cow health and conception, implementing preventative fly control strategies are key to protecting your herd and profit from horn flies.

The easiest way to use a preventative control for horn flies is to use a feed-through larvicide or insect growth regulator (IGR), like Altosid® IGR, which allows the cattle to treat themselves by simply adding it to your current feed or mineral program, reducing both time and labor. Altosid® IGR is a feed-through larvicide that breaks the life cycle of horn flies by targeting the immature stage before they are able to emerge as adults. The active ingredient, (S)-methoprene, is unique to insects, interrupting the transition into biting adults.

Effective Horn Fly Control with Altosid® IGR

To ensure success with Altosid® IGR, implement and follow the tips below. By following the tips outlined, you can help limit the number of horn flies produced on your pastures and impacting your cattle.

For Success:

  • Begin feeding product with Altosid® IGR 30 days before the average last frost in the spring
  • If feeding in free choice feeds such as mineral supplements:
    • Put out a 5- to 7-day supply and allow one feeder per 15 to 20 cattle.
    • Place near watering or loafing areas. 
  • Monitor feed consumption for a few days. Increase or decrease the number of feeders or move them if necessary to adjust for proper consumption. Ensuring appropriate consumption is key to product effectiveness.
  • Continue feeding product with Altosid® IGR for 30 days after the first frost to limit the number of horn flies overwintering and jumpstarting the population in the following spring.

In most years, Altosid® IGR alone provides excellent season-long control when used as directed. If fly populations exceed acceptable levels or an Altosid® IGR supplement is started after horn flies are present, use Starbar® Prolate/Lintox-HD™ Insecticidal Spray & Backrubber for Livestock, Cattle Armor™ 1% Synergized Pour-On, or Inhibidor™ Insecticidal Pour-On to knock back the adult fly population.

While you will never eliminate all flies on cattle, maintaining a fly control program will help keep the horn fly population under the economic threshold, and protect your herd’s health and bottom line. Altosid® IGR is available in mineral blocks, tubs, liquid feed supplements and as a premix that can be top dressed or mixed into feed. Visit AltosidIGR.com to learn more. 

Altosid, Inhibidor, Prolate/Lintox-HD and Starbar are trademarks of Wellmark International.

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