Summer is here with the arrival of June, and so is our annual horn fly population across Greenwood County. Horn flies are small in size, approximately 3/16” in length and are usually found on the backs, sides and poll area of cattle. During a warm summer afternoon they can be found on the belly region of cattle.
According to University of Nebraska Extension, economic losses associated with horn flies are estimated at more than $1 billion dollars annually in the United States.
Horn fly feeding causes irritation, blood loss, decreased grazing efficacy, reduced weight gains, and diminished milk production in mother cows.
Male and female flies, acquire more than 30 blood meals per day per fly. Populations of these flies tend to peak in June and the hot dry days of summer tend to decrease the overall population at that time.
However, in late August to September as the temperature begins to decrease and humidity increases, the horn fly population tends to peak again.
The common classes of fly control products are pyrethroids, organophosphates, macrocyclic lactones, and insect growth regulators. These products are approved to be used by a number of different application methods. Understanding of the product label is very important; please read these labels carefully!
Many producers use insecticide impregnated fly tags to provide fly control for the majority of the grazing season. It is important to note what class of ear tag is used on a yearly basis.
Resistance is a real concern and proper steps should be taken to help mitigate it. Several generations of flies occur during the grazing season. During the multiple generation turnover, flies do develop some level of resistance in continued presence of a parasiticide.
It is important to remove spent fly tags once they have lost their efficacy. The sub-therapeutic levels of product left in the tags hasten development of resistance. It is also recommended to switch classes of fly tag (not just brand) on a yearly basis.
If placed too early in the season, the fly tags will lose potency and efficacy late in the season when the fly burden will be peaking once again. Depending on the tag, length of expected efficacy may be 3 to 5 months. So extra steps may be needed when the fly tag loses its effect.
Providing a late season treatment after the fly tag has run its course can be extremely successful for a number of reasons.
Changing the class of parasiticide at this time, and using a spot-on/spray treatment will reduce the number of resistant flies that overwinter. It also reduces the overall population in the area. This helps continue the success of the fly management product rotation from year to year.
The spot-on/spray products are shorter acting (2-4 weeks in length. Since they have less residual activity, they carry minimal risk of developing resistance when used at this time.
Timing of application and product use are always important topics to review with your local veterinarian to develop a site specific pest management plan.
If you have questions regarding fly control or other general livestock related questions, please contact Greenwood County Agriculture Extension Agent Clint Laflin. Laflin can be reached at 620-583-7455, or [email protected].
