While visiting some farms this spring to help work cattle, I have noticed that flies are out in high numbers in some places but not so much in others. Unfortunately, they will come! Usually I get the question, “What is the best thing for flies?” There isn’t really a “best thing” for flies. What works in one herd may not in another. The producer with 20 cows may have more time to devote to the herd than a producer with 200. There are many control programs and all can be effective. Each producer should consider the options and choose the one that is best for his individual situation.
Horn flies are probably the most important economic fly pest on the list. They are called horn flies because they tend to congregate at the base of the horns on horned cattle. In this area we typically find them on the shoulders, down the backs, and on either side of the tail head on cattle. As the population gets larger, they will spread down the sides onto the legs. Horn flies feed on blood and tend to feed continuously while on the animal. Five hundred horn flies will remove a pint of blood each day from the host animal. While a cow is a large animal with a fairly large blood supply, it won’t take many days to become anemic losing this much blood each day. In the middle of summer, it is not uncommon to find as many as 2,000 flies on an untreated cow and 4,000 to 5,000 on untreated bulls. Horn flies remain on the host animal all the time. This fact aids in our efforts to control them.
Face flies, houseflies, and lesser house flies do not feed on blood but cause problems by pestering the cattle and spreading certain diseases. These flies feed on the secretions from the eyes and nose of the host animal. Obviously, this would be a source of constant irritation to the animal. There is also evidence that these flies help spread pinkeye in the herd. All three of these fly species tend to move from animal to animal, never spending much time on any individual, which makes controlling them more of a challenge.
Stable flies are blood feeders like horn flies but their feeding pattern is like that of the face and houseflies. They tend to move from animal to animal feeding on each as they go. Stable flies have been implicated in the transmission of anaplasmosis in cattle. Anaplasmosis is a blood disorder in cattle that is on the rise in southern herds. These flies can be effectively controlled by cleaning up old hay piles around feeding sites so that they have no place to lay eggs.
So what can we do to control these pests? Two insecticides are on the market that can be fed to the animals through various carriers, the most common being a mineral supplement, which is then excreted in the manure. The flies lay eggs in the manure for the developing larvae to feed on. The insecticide in the manure stops the larval development and therefore eliminates the emergence of adult flies. These insecticides have no affect on adult flies. Since the adults only live for 2 to 3 weeks, control is achieved after this first generation dies. However, if a neighboring herd (within 2 to 4 miles) is not under a fly control program, there can still be large numbers of adult flies present. This would dictate using an additional control method or a completely different strategy.
Other control methods include insecticide ear tags, back rubs, dust bags, and hand-applied sprays, dusts, and pour-ons. The insecticide ear tags, also called fly tags, offer very effective control by killing flies present on the animal and repelling flies that may come at a later date. Fly tags should not be applied until there are approximately 200 flies per animal present and should be remove in the fall to help prevent pesticide resistance in the fly population. To further prevent the pesticide resistance, producers should rotate tags used by active ingredient. Use an organophosphate tag for two years followed by a pyrethroid tag for one year. Most fly tags on the market offer protection for 4 to 5 months. Back rubs and dust bags charged with pesticide are very effective in controlling flies if placed where animals will use them. Many older cattle will voluntarily use these but others must be forced to use them. Placing them so that cattle must go under them when accessing water or minerals or from one pasture to another can do this. The drawback to these devices is that they must be recharged every week or two. Many times we put them up and then forget to service them during the summer. The sprays, dusts, and pour-ons work well in most cases. The biggest problem associated with these is their need to be re-applied every 2 to 3 weeks. This becomes very labor intensive. Most of the pour-ons on the market now will provide longer control but still won’t last all season. One product now claims to have nine-week effectiveness, indicating that you can treat cattle twice during a year and have season long control.
Failure to implement a fly control program for your herd causes reduced performance and lost income. It is generally thought that every $1 spent on fly control returns $5 to $10. Some producers think they can’t afford to control flies. Truth is, they can’t afford not to.
Paul Gonzalez is an extension agent with the Sampson County Cooperative Extension Center specializing in livestock. You can reach him by calling 910-592-7161.