In pasture settings, the most economically damaging fly is the horn fly. Good control can mean an additional 12 to 20 lb.of weight gain per calf over the summer

Insecticide ear tags can provide good control of horn flies and may reduce face-fly numbers. (Photo by Doug Ross)
Insecticide ear tags can provide good control of horn flies and may reduce face-fly numbers. (Photo by Doug Ross)

months and reduced weight loss for nursing cows.

Face flies, meanwhile, can disrupt grazing during the day and can spread pinkeye.

Following are some application tips for dust bags, insecticide-impregnated ear tags, back rubbers and animal sprays.

Dust bags are most effective in forced-use situations where cattle have to pass under them regularly as they move to drink or eat.

The bottom of the bag should be low enough so that the animal must lift it with its head to pass through. This provides good insecticide placement to manage face flies. The animal is treated for horn flies and other biting flies as the bag drags along the backline.

Keep dust bags charged with insecticide and protected from rain. Dust formulations will clump if they get wet, and the bag will not dispense the insecticide properly.

Insecticide ear tags can provide good control of horn flies and may provide some reduction in face-fly numbers. Install tags after flies first appear in the spring. Check label for limits. Some products state that calves less than 3 months old should not be tagged because ear damage may occur, or should receive only one tag.

Horn-fly resistance to insecticides, particularly pyrethroids, is an increasing problem. If insecticide resistance is suspected, use tags containing an organophosphate insecticide or abamectin.

Remove tags at the end of the fly season or before slaughter. Protective gloves should be worn when applying and removing tags.

Concerning oilers or back rubbers, use diesel, No. 2 heating (fuel) oil or label-recommended mineral oil to dilute the insecticide. Do not use waste oil or motor oil.

One gallon of oil solution per 15′ to 20′ of back-rubber cable is sufficient for 30 to 40 head.

As with dust bags, these devices are most effective when placed in force-used areas such as mineral stations or entrances to watering sites. Oilers are more effective against face flies if fly flyps (strips of cloth hung from back rubbers) or fly bullets are tied at 4″ to 6″ intervals along the length. Service the devices at least once per week.

Use a power sprayer for complete coverage when applying insecticide sprays for pasture-fly control, but be especially careful to not contaminate feed or water. Use a coarse spray rather than a fine mist when applying sprays, so that the animal’s coat is thoroughly wetted.

Among the alternative options, a compressed-air gun can be used to dose animals with capsules containing a lambda-cyhalothrin pour-on formulation.

Several feed additives (oral larvicides) that target fly maggots breeding in fresh manure are available.

Methoprene, an insect-growth regulator (IGR), is available in block, tub and liquid products for horn-fly control.

Diflubenzuron, another IGR, can be administered as a feed additive. This chemical prevents the insect from forming its external skeleton that is required for survival.

Bayer also offers an organophosphate insecticide that is available as a premix for horn and face fly control.

All animals must eat a minimal dose of a feed additive regularly, and supplementary control measures must be taken to deal with flies moving in from nearby herds.