We’re in the heat of summer, a welcome time for many reasons – warm sunny days for putting up hay crops, ripening fields for harvest season, cattle contently foraging and perhaps even some trips to the river or lake for fun. What is not welcomed, however, by the cattle or producer this time of year are flies.

Small meranda
Idaho County Extension Educator / University of Idaho

External pests – such as horn flies, face flies and stable flies – can reduce time spent grazing, reduce weight gain of a calf, add to weight loss in mature cows, contribute to the spread of bacteria such as pinkeye and, if severe enough, can lead to a weakened immune system. Fortunately, there are several management methods to consider in controlling flies, including back rubbers and dust bags, feed additives, high-pressure sprays, insecticide boluses, insecticidal eartags and pour-ons.

When determining which method will be most effective in your operation, consider the benefits and constraints of each. Back rubbers and dust bags allow cattle to self-treat while scratching. However, dust bags will only be most effective when they are placed in a spot where cattle must pass under daily, such as going to water. If the cattle are not forced, in some way, to come into contact with these methods, fly control will not be as impactful.

Feed additives work by incorporating the insecticide into mineral supplements that are supplied in block, tub or loose form that cattle have free access to. These then pass through the digestive system of the animal and prevent the larvae from maturing in manure. Similar to the effectiveness of rubbers and bags, it is difficult to ensure an animal is consuming an appropriate dosage.

A convenient method to consider would be the application of an insecticide eartag. These tags have one or more insecticides embedded that, with movement of the head, slowly release small doses over time that travel through the hair coat of an animal. Be aware that horn flies do have some resistance to the active ingredients in tags. It is also recommended to use high-quality tags and rotate between tags with different active ingredients to reduce resistance.


Pour-ons allow for quick application directly onto the backs of cattle, with effectiveness lasting for several weeks. There are many product options available, some that are effective against horn flies. Efficacy is dependent on correct dosing and because efficacy wears off after several weeks, re-application would need to be done throughout the grazing season.

With each method presenting positive outcomes and limitations, it is worth considering implementing two methods for the season to ensure more control of flies and overall improved herd health status.