Controlling flies around livestock is important to profits

Summertime is here and with it the problems associated with flies on livestock.
The number one fly problem is horn flies. These pests are easily recognized as they are small flies with V-shaped wings that like to position themselves with their heads downward on the backs and shoulders of cattle.
They are unique in that they spend almost all of their time on the cattle, leaving only long enough to lay eggs in the manure.
Their life cycle is very rapid, often completing as many as eight reproductive cycles in one summer. This presents greater opportunities for genetic recombination and is a major factor in the development of resistance to pesticides.
The economic threshold for horn flies ­— the level of infestations where it pays to treat for them — is about 200 flies per animal. Below that level they may be a nuisance to the cattle, but don’t really cause economic losses. Above the threshold, they cause decreased milk production and lower weaning weights.
A study done in Nebraska showed that when there were 500 flies on the cows, the weaning weights of the calves were decreased by 8 percent. This kind of loss can pay for a lot of spray treatments.
To estimate the number of flies, count them with binoculars on one side of the cow and double the rough count you come up with. Select a few animals at random to get an estimate of the status of the herd.
Ear tags, sprays, back-rubbers and dust bags are all effective against horn flies, but it may take a combination of several methods to keep the counts down all summer. The insecticides that are commonly used are chlorinated hydrocarbons, organophosphates, and pyrethroids.
It is probably wise to rotate between these groups using one or two for the duration of the summer and then changing to a different combination the next summer. This will help to slow the development of pesticide resistance.
One of the issues with using ear tags is the potential of building insecticide resistance. Historically, more resistance has been reported after using a pyrethroid tag. It is recommended that cattlemen should not use the same ear tag two years in a row but rotate with different ear tags.
When rotating a rancher should try using products that are in different chemical classes such as the following recommendation:
• Year one: Chlorinated Hydrocarbon.
• Year two:  Organo Phosphate.
• Year three: Pyrethroid.
Usually all ear tag products recommend putting two tags per animal for sufficient insecticide coverage. If control fails after two months from initial tagging then all tags should be cut out and a different treatment option should be applied such as dust bags.
Also, if control fails when using ear tags the alternative insecticide application should include a product that is in a completely different chemical class from the failed ear tag.
Research has shown that when using dust bags in a force-use system (placing the dust bag in a location that forces the animals to go under it, such as near a water tank) they provide up to 80 percent control of horn fly populations.
Stable flies are larger flies that are on the cattle only long enough to feed and then go elsewhere; often around barns, pens or shady loafing areas.
The number of stable flies is directly related to sanitation. These flies lay their eggs in decaying plant materials such as spilled grain, feed or hay. Areas where round bales were stored or fed last winter are special problem areas.
Cleaning up these areas by raking or burning will help keep stable flies down. Pesticides are more effective when used on or in premises than when applied to the cattle.
Horse flies or deer flies are intermittent problems on cattle throughout the summer. These flies represent several different species that are present only for a short while after they hatch. Because, however, there are different species, they have different hatching times, thus the intermittent appearance.
Scheduled sanitation practices will keep fly levels down on your premises. Scouting your livestock is the best way to prevent flies and other pests from having a negative impact on your livestock operations. When you see that flies are be-coming a problem on your livestock, timely insecticide applications can prevent fly populations from cutting into your profits.
If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office, or visit our web site at http://countyext.okstate.edu/pottawatomie/.