Effectively controlling flies requires a holistic approach and good pre-planning. In order to reduce the deleterious effects these small pests have on cattle, eliminating the fly population early on is important, but if it’s done too early, resistance to available pesticides is inadvertently built. Not only is it an economical issue in reduced milk production and weight gain, it is also an animal welfare issue given the stress these pests cause from biting and just generally being a nuisance.

Before approaching fly management, you need to know the pest you’re dealing with. The major flies of concern are face flies, horn flies and stable flies.

* Face fly.

This nonbiting pest resembles the housefly and is found around the eyes, mouth and muzzle. They feed on mucous secretions using a raspy tongue that causes irritation. This irritation to the eye can lead to the transfer of pink eye between animals. Face flies only remain on cattle for short periods of times during the day, making them more difficult to control. Eggs are laid in fresh manure.

* Horn fly.

These are biting insects that eat up to 20 blood meals per day and are about half the size of the housefly. They are found on the back and sides of cattle in very great numbers. They migrate to the belly during the hottest parts of the day. When observing these flies, you will see their heads down as they bite and their wing tips up. Nebraska studies have demonstrated calf-weaning weights were 10 – 20 pounds lower when horn flies were not controlled on mother cows. Stocker cattle gain can be reduced as much as 18 percent when horn flies are left unchecked. Like the face fly, eggs are laid in fresh manure.

* Stable fly.

Generally more of a concern in housed cattle, these biting flies can bother pastured cattle. Their nickname, “storm fly” comes from the fact that they are seen on the lower legs of cattle and seem to be more prevalent when a storm is approaching. Similar in appearance to the housefly, these insects will also bite humans, taking several painful blood meals per day. Research conducted at the University of Nebraska, West Central Research and Extension Center utilizing yearling steers, recorded a reduction in average daily gain of 0.44 lbs. per head with animals that did not receive an insecticide treatment compared to animals that received treatment. Eggs are laid in organic matter that has contact with soil, such as rotting hay around feeders and barns.

Photo by JH-Photo /istockphoto.com 

Have control measures in place

Due to the issue of resistance, it is important that management practices be in place to apply control when most effective. While this may not be convenient, control should not start before flies have reached the economic threshold (Table 1). You should make the fly counts on at least five to 10 standing cattle. Ideally, this is done early in the day on a weekly basis. Keeping records will help you decide when to treat and after treatment, if it has been effective.

Face and horn fly control methods will be similar. Back rubbers (oilers) dust bags, insecticide ear tags, sprays and oral larvicides are each effective. A combination of approaches delivers the best product.

Many products can be found online or through supply catalogs; however, not all may be approved for use in your state. In New York you can check which pesticides are available and legal by using the Pesticide Product, Ingredient, and Manufacturer System (called PIMS for short). It’s online at http://pims.psur.cornell.edu and contains data on all of the currently registered pesticides for NYS as well as the NYSDEC approved labels. You can search by a variety of methods including the product name and active ingredient.

As of this writing, the following are legal control products in New York:

Dusts: coumaphos (Co-Ral), tetrachlorovinphos (Rabon) and permethrin (many brand names).

Back-rubbers (oilers) : coumaphos (Co-Ral), permethrin (many brand names), and phosmet (Prolate).

Animal sprays: coumaphos (Co-Ral), permethrin (many brand names), natural pyrethrins, and phosmet (Prolate).

Oral larvicides: diflubenzuron (ClariFly Larvicide is one trade name), methoprene (Altosid), and tetrachlorovinphos (Rabon).

Pour ons: permethrin (many brand names).

Ear tags: organophosphates (Corathon,™ Optimizer,™ Patriot,™ and Warrior™), synthetic pyrethroid (CyGuard,™ PYthon,™ PYthon MagnuM,™ and Saber Extra,™ Double Barrel™VP), macrocyclic lactone (XP 820™).

The stable fly only stays on cattle for short periods of time, therefore control is more difficult. Currently the best and only control of this pest is insecticide sprays. Removal of organic debris (old round bales, manure piles, etc.) will reduce breeding areas for stable flies and may reduce the population.

Special notes

For the most effective system, you should consult your veterinarian to develop a complete program that suits your environment and management system.

Back rubbers and dust bags are most effective when cattle are forced to use them (for example, when going to water or mineral feeders).

To reduce risk of resistance, it is important that you follow labels explicitly and rotate active ingredients every two years. If the label states that you use two tags per animal, do not try to use just one. Likewise, if best control is indicated by using on calves and cows, follow this directive. Finally, also note that some tags are not for use on calves less than 3 months of age. Finally, it is important to remove tags at the end of fly season.

There is a wealth of information on use of several different types of fly traps, which can be viewed at Fly Management in the Organic Dairy Pasture – eOrganic Webinar.