Horn flies can be a frustrating pest to deal with. There is no perfect strategy for controlling them, and the most successful strategies generally require more than one approach. The most frequently used options to control horn flies include topical insecticides and the use of insect growth regulators. Another strategy some folks are having success with is a walk-through fly trap.
When using topical insecticides, it is important to consider how long an application will typically last and how easy it is to gather the cattle and apply the insecticide throughout the season. Additionally, it is important to consider what chemical classes are available within an application method to allow for rotation of chemical classes.
Topical insecticides can be applied through eartags (aka fly tags), pour-ons, sprays, dusts, rubs or gel capsules. Unfortunately, due to horn flies developing resistance, none of the insecticides work as well as they did when they were originally released. However, when used appropriately, they can still provide good benefits.
Of these options, fly tags will provide the longest control, and applying two tags per animal will provide better control than just one tag. Fly tags should be placed on the bottom third of the front side of the ear. The insecticide is slowly released from the tag over time and, as cattle groom themselves, the insecticide is transferred from the eartag onto the animal. It is important to remove fly tags in the fall to help reduce horn fly resistance. Using a pour-on at the same time fly tags are applied can provide additional benefit.
Pour-ons and sprays work well when it is easy to gather cattle and treat them multiple times throughout the season. Rubs and dust bags can be successful if placed where cattle are forced to use them.
Insect growth regulators work by preventing eggs from developing into adults. They are typically delivered in a mineral supplement or with a bolus. Methoprene is a common insect growth regulator added to mineral at either a 0.01% or 0.014% concentration. For most operations, it is critical to use the 0.014% concentration to provide an adequate dose based on current cow weights.
Walk-through fly traps won’t work for all operations but could be used when rotating cattle from pasture to pasture or forcing cattle to come through them to access a water source.
