Jonathan Cammack, assistant professor and state Extension specialist, livestock entomology and parasitology, is offering herd health advice as part of the weekly series known as the “Cow Calf Corner,” published electronically by Dr. Derrell Peel, Mark Johnson, and Paul Beck. Today, Cammack gives advice on getting an early start on fly season.
As we finally start to warm up, it’s never too early to start thinking about our fly management program for the upcoming season. Management of horn flies should be approached from multiple angles, using as many of the tools as we have available. A two-pronged approach of combining insecticide products targeted at different life stages, such as an ear tag for adult control, and a feed-through insect growth regulator (IGR) for larval control, will give you the highest probability of success in the battle against these pests.
Ear tags are an effective method for control of adult horn flies and should be administered to the animals once the threshold of 200 flies per animal is reached. Most ear tags have an effective life of approximately 4 months, under ideal conditions. In the hot, Oklahoma summers, expect the lifespan of an ear tag to be 3 months or less. Waiting to tag animals until horn fly numbers reach the threshold of 200 flies per animal will help ensure that the ear tags are still effective once we reach peak fly season in mid to late summer. If horn flies are active: it’s never too late to tag, but it can be too early. Make sure to use a different chemical class than you did last year, to help slow the development of insecticide resistance. If picking a synthetic pyrethroid tag, choose one that is synergized, and contains piperonyl butoxide (PBO) as an active ingredient. A good, yearly rotation schedule for ear tags is shown below.
IGRs are a great method for managing larval horn flies, and larvae of other biting and nuisance flies that develop in decomposing organic matter such as manure. Feed-through IGRs are consumed by the cattle, and pass through their digestive tract and are excreted in the manure, which serves as a food source for larval flies. When the larvae consume this IGR in the manure, they will not successfully complete their development to the adult stage. Start feeding minerals or supplemental feeds containing IGRs during the month of March and continue through October. We want to make sure all of the manure in pastures contains the IGR, so we can start to have an impact on developing fly larvae (particularly horn flies) as soon as the adults become active and start laying eggs in the manure, and throughout the remainder of the fly season. Products that are registered as feed throughs for cattle contain either the active ingredient Methoprene (examples: Altosid® IGR, Dipteracide®, Pertinent IGR) or Diflubenzuron (examples: ClariFly®, JustiFly®, HerdGuardTM). If you have been feeding your cattle hay over the winter, it is likely that the hay, manure, and urine mixture surrounding your round bale feeding sites is a breeding site for stable flies. During the spring, as it starts to rain more frequently, this wasted hay can remain wet, and continues to be a source of development for stable flies. Premise granular IGR products such as Novaluron (ExhaltTM WDG) and Cyromazine (flynexx® granules) can be spread around on top of this wasted hay surrounding the round bales. These products will dissolve and come into contact with or be consumed by larval stable flies and prevent their development to the adult stage.
Taking the two-pronged approach outlined here can help minimize the impacts of horn flies and other nuisance and biting flies on your herds.
