Includes Ixodes spp. and Dermacentor spp.
- abamectin ear tag (Tri-Zap)-One tag to each ear of all animals when ticks appear. Remove tags at end of season or before slaughter.
- diazinon/chlorpyrifos ear tag (Warrior)-One tag to each ear of all animals older than 3 months when pests appear. Remove tags at end of fly season or before slaughter.
- essential plant oils (Essentria IC3)-Apply at 30 to 90 ml (1 to 3 oz) per gal mineral oil. Spray directly on animal in amounts to cover.
- permethrin/piperonyl butoxide pour-on (Ultra Boss) at 3 ml per 100 lb body weight. Maximum of 30 ml (1 fl oz) per animal. Treat once every 2 weeks as needed.
- permethrin spray (GardStar 40% EC)-Apply at 30 to 118 ml (1 to 4 fl oz) per 25 gal water (0.013 to 0.05% ai). 1 to 2 quarts coarse spray over body of animal, thoroughly wet.
- zeta-cypermethrin/piperonyl butoxide dust (Python Dust)-Apply at 2 oz per animal. Apply in dust bag, shaker, dusting glove, or mechanical duster. Repeat as needed but not more often than once every 3 days.
Management of Resistance to Pyrethroid Insecticides
Horn fly resistance to pyrethroid insecticides is in all cattle-raising areas of the United States. Strategies for combating the flies, while minimizing further buildup of resistance, need to be addressed. If you treat the herd with the proper dosage of a pyrethroid, but within days of using it see many more flies than before the treatment, then resistance is likely. This resistance may be to a spray, dust, or ear tag treatment. Remember that the following guidelines pertain to horn flies only. If resistance is suspected, do not use pyrethroids.
The following control strategies are recommended (may be used singly or in combination):
- Do not treat for horn flies. Cattle can tolerate moderate levels of horn flies (up to 200 per head), so no treatment at all is an option. This has the greatest effect on reducing or slowing insecticide resistance.
- Separate mature animals from calves. There is no evidence that horn flies affect mature cattle, other than reducing milk production in lactating cows. Calves should be treated to optimize weight gain. However, cows without calves and replacement heifers (animals for which efficient weight gain is not imperative) probably should not be treated. With cow-calf pairs, it is more effective to tag cows than calves. Calf weaning weights have been shown to be greater when cows are tagged because of higher milk production. Generally, horn flies aren't a problem on calves until the end of the season.
- Use a four-year rotation strategy to prolong the effectiveness of insecticide-impregnated ear tags. An example of a rotation follows: for the first year, use tags impregnated with abamectin; the second year, use endosulfan tags; the third year, use an organophosphate ear tag; and the fourth year, use a pyrethroid tag. With this plan, a different class of insecticide with a different mode of action is used each year.
- Delay control until flies exceed the treatment threshold. To avoid wasting insecticide and getting poor results, do not apply until horn flies build up in the spring or summer. However, show cattle or other special animals may require intensive treatment.
- Treat periodically with organophosphate sprays, dips, backrubbers, ear tags, oilers, or dusts to reduce early buildup of fly populations. Insecticide resistance can be delayed or reduced by periodic treatments that give high levels of immediate control, followed by a period of no control during which time the pest population again builds up. One to two treatments in early summer may delay the need for more sustained controls.
- Use feed-through fly control products that contain insect growth regulators instead of pyrethroid products. These products are fed to cattle during the months when flies are present. The risk of insecticide resistance development is very low for insect growth regulators such as s-methoprene and diflubenzuron.
- Treat late in the season. This should begin before the horn fly enters its overwintering phase. Any effort to reduce the number of flies that overwinter may hold down the initial density of flies the following spring. For late-season control, use an insecticide with a different mode of action than the one used during peak periods. If flies are not a problem late in the season, skip the late-season control.
- Remove ear tags in the fall; this eliminates the low insecticide pressure during the winter that could foster the development of resistance.