Fly Control Through Manure Management

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Horse manure is the primary source of life for a variety of flies, including biting stable flies and face flies. Stable flies are the most common flying pest to bother horses. They can cause misery with their painful bites. Face flies feed on the secretions of the eye, nose and mouth, and they can cause severe irritation and spread bacterial disease to a horse’s eyes if left unchecked.

According to information from the University of California Agriculture and Natural Resources (UCANR) agency, the stable fly can develop from egg to adult in 12 days if it has the right type of material for breeding. Piles of moist, decaying plant material, such as hay mixed with manure and urine, are ideal areas for stable flies to breed.Face flies require fresh manure for development.

Fly control is most effective when efforts are focused on eliminating the larval stage. This means eliminating sources of fresh manure.

By removing material in which the larvae develop, the life cycle of the fly can be broken, preventing subsequent production of adult flies, according to the UCANR.

Manure should be cleaned from stalls or paddocks at least once daily—more often, if possible--and stored it in sealed containers, or spread out thinly to dry in the sun or composted properly to prevent the hatching of the eggs. Manure in pastures should be spread out so it can dry quickly in temperatures warm enough to prevent hatching.

Feed-through fly control products are another method of making manure inhospitable to stable and face flies. Keep in mind there is no research that shows "natural" products, feeds, or supplements containing diatomaceous earth as the active ingredient are of any value in reducing fly populations (or internal parasites). There are some studies that show diotomaceous earth has no effect.

Traditional feed-through fly control products that contain chemicals that inhibit the fly’s ability to develop normally after it hatches in treated manure are proven to work.Feed-through fly control products are added to a horse’s grain. They pass through the body of the horse without detrimental effects to the horse, then are eliminated along with the manure. The manure is thus "treated" and flies are inhibited.

The following information from the University of Nebraska-Lincoln can help you better understand how feed-through fly control works. To read this entire article visit their website.

There are a number of insecticidal products that control adult flies, including premise sprays, bait stations and on-animal insecticides. These provide only temporary relief and must be reapplied frequently.

However, there are some newer products that control larval flies at the source, in the manure. The active ingredients of these products are known as insect growth regulators (IGRs) which interfere with growth and development of fly maggots.

The life cycle of a fly consists of egg, larva (maggot), pupa and adult. The adult female fly lays eggs in manure or other suitable organic matter. The eggs hatch into tiny maggots, which feed on the manure. These maggots molt several times to larger stages. When maggots reach maturity, they pupate, later emerging as adults.

There are two active ingredients found in IGR products registered for fly larval control on horses: diflubenzuron and cyromazine. Diflubenzuron and cyromazine are called chitin synthesis inhibitors because they interfere with the formation of chitin, the primary component of the insect cuticle (the skin). Insects exposed to these IGRs will not molt properly so most of the maggots will die when they molt and flies will not emerge from the manure. These products control the flies while in the manure and are more efficient than relying on fly sprays.

Diflubenzuron is found in the feed-through products SimpliFly and Equitrol II, manufactured by Farnam. These products are identical. SimpliFly and Equitrol II are top dressed on grain or mixed with the ration to provide 6.8 mg per 100 pounds of body weight. For a 1,000-pound horse, the dosage is 1 ounce Equitrol II or SimpliFly per day.

The product containing cyromazine and registered in Nebraska for horses is Solitude IGR. It is an alfalfa-based pellet, manufactured by Pfizer Animal Health. Dosage of Solitude is not based on body weight, but each horse should be fed 1/2 ounce Solitude per day.

Because molting is a process only arthropods do, warm-blooded animals, including birds and mammals will not be affected by IGRs. Studies have shown these products are safe for horses, other mammals (including humans), beneficial insects and non-target organisms.

For best results, start feeding these additives before the beginning of the fly season, continue through the summer and into the fall until cold weather reduces fly activity.

If you decide to use an IGR larval control product mid-season, you may need to use products that control adult flies (such as on-animal insecticides, premise sprays and bait stations) until the IGR product gets the population under control. Then use these additional products only as needed.

These products are often sold where equine feed and supplies are sold or through veterinarians. In the Lincoln area, these products can be found during fly season at Fort Western and Tractor Supply Company (both locations). These products can also be purchased from internet vendors.

Sometimes flies will not be controlled as well as one would like. This can occur when:

  1. Sanitation is not good. Flies breed in organic matter other than manure. Spoiled feed or hay, wet bedding, grass clippings, poorly managed compost and other organic matter will breed flies. These IGR feed-through products only control flies breeding in manure.
  2. For some reason, horses do not get the recommended daily IGR dose. If you do not have the ability to control dosing, control may not be achieved.
  3. Other livestock or pet waste is producing flies.
  4. Flies from surrounding areas travel to your equine facility. If your neighbor has livestock/horses and is not controlling his fly population, even the best fly management will be compromised. Studies have shown flies can travel considerable distances, but most house and stable flies will only travel a mile or two.
  5. Resistance by flies to these IGR products is possible, especially if you use the same product year after year. If the product you have chosen seems to lose its effectiveness over time, you may need to use a different product or approach.