Shoo fly: Now is the time to think fly control

horse fly

“Shoo fly!” is a what many grazing livestock, especially beef cattle are likely thinking during the summer months. 

As we think about options for fly control on pasture, we have several options and combinations to choose from. 

We can minimize the impact of flies on the herd by managing the fly population in spring and early summer. In order to do so, timeliness is key to having season-long success. 

Fly impacts

Blood loss, irritation, annoyance, insect transfer of disease are direct losses caused by flies. Among many other bovine diseases, flies are able to transfer pathogens that cause mastitis, pinkeye and anaplasmosis. 

Indirect losses due to heavy fly pressure include decreased weight gain and lost performance. It’s estimated that insect pressure on beef cattle causes several billion dollars in losses annually. 

Types of flies

On pasture the two species of fly that are of greatest concern are the horn fly and the face fly, while the house fly is the most abundant pest in confinement livestock operations.

While all flies are pests and a nuisance to livestock there are several differences between the two main pasture fly species. 

  Horn fly: The horn fly is an aggressive fly that will take 20-30 piercing blood meals a day from the host animal. Ninety-five percent of horn flies will be on the host animal at a given time and require fresh manure to pupate and become adults. Horn lies can be found in rather large numbers on the backs and side of the livestock. The economic threshold and an acceptable goal is to have less than 100 horn flies per side per head of cattle. 

  Face fly: Face flies tend to be less aggressive than horn flies and are often found near the face of the animal. At any given time, only 5% of a fly population may be active in an animal attempting to get a blood meal. Often the adult face fly will take shelter in a barn or other shelter near the livestock. A management goal is to have less than 10 face flies per head. 

Methods for control

For the two main pasture flies, fresh manure piles are key to reproduction and developing the next generation. One reason to think about fly control in March/April is that we can potentially reduce the reproductive success of the earlier generations of flies. 

This can be done by feeding mineral additives that pass through the cattle and regulate insect growth within the manure piles. 

For these insect growth regulator products to be effective they need to be fed 30 days prior to and 30 days after fly season, hence why we are discussing flies in late March. 

These products, while effective at managing fly populations do have some pitfalls. For maximum efficacy, required intake of the IGR product must be met by each animal in the herd. Some conflicting research shows that feed-through insect growth regulators may or may not damage dung beetles. 

Also, adult horn or face flies are not affected by feeding IGR products to livestock, only larvae in fresh manure. 

Fly season is right around the corner, use previously mentioned thresholds for fly management and control them when necessary. Oilers, dust bags, rubbers and insecticide ear tags can also be used in a fly management program. Discuss control options with your veterinarian or local OSU extension educator.


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