The goal of horn fly-management programs is to reduce the numbers of feeding adults on the animals and manage pastures to minimize larval survival.
Because horn flies only lay their eggs in freshly dropped, individual dung pats, cultural manure-management practices are not practical. This is in contrast to house and stable flies, which can breed in manure accumulations in confinement operations.
Good management practices that emphasize forage production and internal parasite control, such as pasture rotation, will also help reduce manure accumulation. In most well-managed pastures, insects such as predatory wasps, mites and dung beetles may help reduce horn fly populations by feeding on the fly larvae.
The excessive and inappropriate application of some deworming agents and insecticides may compromise the effect of natural fly enemies, especially dung beetles.
Because the horn fly spends virtually all of its time on the cow, insecticides are an effective tool in horn fly control.
If not treated for horn flies, young cows, replacement heifers or other growing stock may experience decreases in growth or weight loss; therefore, young cattle may require closer observation and more treatment than non-producing or fully grown cattle will.
Insecticide products effective for horn fly control include ear tags, residual livestock sprays, pour-ons, dust bags, back rubbers and oilers.
Ear tags containing pyrethroids, abamectin or organophosphates may be useful in horn fly control. The insecticides are gradually released from the tag onto the body surface of the cow.
Cattle producers can improve ear tag effectiveness by:
- following manufacturers’ recommendations; for example, using one tag in each ear (two tags per animal) when suggested
- applying the tags when approximately 100 flies per side of the cow (200 per animal) are first observed
- removing and properly disposing of ear tags at the end of the fly season
- rotating chemical classes yearly.
Horn flies become resistant to pyrethroids (fenvalerate, permethrin, cyfluthrin, lambda cyhalothrin, zeta-cypermethrin) much more quickly than they do to abamectin or organophosphates (diazinon, coumaphos, pirimiphos-methyl, diazinon+chlorpyrifos).
Thus, herd records detailing the type, manufacturer, time of application and results from year to year help producers make better decisions on future ear tag purchases. Note: Always wear protective gloves when applying and removing ear tags.
Residual fly sprays and pour-ons can be used to supplement other forms of fly control when more than 200 flies are estimated per side.
Pyrethroids, organophosphates, spinosad and avermectins are the most commonly used chemical classes. Accurate records should be kept and resistance (or lack of efficacy) noted so that the chemical class can be avoided in future treatments.
Self-treatment devices such as dust bags, oilers, face mops and back rubbers can be very effective in some cattle operations. Placement sites for such self-treating devices are critical to their usefulness, as frequent contact with the animals is imperative.
Installing these devices in alleyways, chutes and entrance areas for trace-mineral dispensers and feed-supplement feeders will ensure contact with an animal’s head, back or sides.
Feed-through products containing diflubenzuron and methoprene (insect-growth regulators) or tetrachlorvinphos (an organophosphate) are available to be mixed with feed or minerals to prevent development of immature stages of flies in manure of treated cattle.