This applies to horse fly management but the principles work as well for chicken stuff...

To achieve the greatest reduction of flies, you should employ a combination of measures that work hand-in-hand.

Cultural Control ("manure management")

Use good sanitation practices. No fly control program will be successful if manure is allowed to pile up around the premises. The most effective method of manure management is to spread it thinly on fields where it will dry quickly as the pest larvae are highly susceptible to this drying process. If spreading isn't practical, the manure should be piled high. This reduces the surface area and results in heat generation within the pile, driving the pest larvae to the surface within reach of the control method.

Elimination of as many wet areas as possible and the use of hydrated lime on the areas where your animals urinate frequently are also helpful.

Trapping

A great many trapping products are available for reduction of fly populations. Check out the sources at the end.

Biological Control

Two kinds of beneficial critters do a great job of minimizing fly problems.

The fly larvae can be controlled by using beneficial nematodes (Steinernema feltiae).

Nematodes are microscopic, non-segmented worms that occur naturally in soils all over the world. Apply nematodes to ground area where fly larvae are present. Mix with water and spray or sprinkle on the soil along fence posts and on manure piles. Moisten area first if soil is dry. Always release nematodes in the late afternoon when temperatures are cooler. Apply 5-10 million nematodes/25 sq. ft. manure pile. Release every 3-6 weeks or until infestation subsides.

These nematodes do not harm earthworms.

The fly pupae can be controlled by using other, specific fly parasites -- gnat-sized, nocturnal, burrowing wasps that do not bite, sting, or harm humans or animals.

There are four such fly parasites (actually "parasitoids"): Mucidifurax zaraptor, Mucidifurax raptorellus, Nasonia vitripennis, and Spalangia cameroni (for use in summer months only).

These species are able to complete a generation every two to three weeks. For several reasons, however, the parasite population needs continuous reinforcement to maintain a high level of fly control. The main reason is that the flies have a distinct advantage in actual numbers produced. A single fly will lay up to 800 eggs, but a single parasite will attack only up to 50 fly pupae. Also, the life cycle of the fly is much shorter than that of the parasite. The fly simply reproduces more often, contributing to the pest's advantage in reproductive capability.

The wasps are shipped as parasitized pupae in a sawdust medium and are dispersed by releasing a small handful at "hot spots": for example, manure collection sites; under water troughs; along fence lines; below straw bedding; around mill areas, silage pits, and other feeding sites.

At the edges of these hot spots, scratch a 1/2 inch hole in the ground with your boot heel, drop in a small handful of sawdust and pupae, and cover with them with straw, earth, or manure to protect them against wind, birds, or pesticides.

The parasites may travel almost 200 feet in search of viable fly larvae and pupae. Repeat this release procedure in slightly different spots on subsequent applications. In this way, new cultures of parasites will be evenly distributed throughout the fly season.
A third biological control organism works well under very moist conditions. "Bti" (Bacillus thuringiensis israeliensis) is a bacterium that kills fly larvae. It is available in granular form and is used on wet manure piles and other spots on the ranch where water stands or keeps the area damp.

Chemical Control

Use pesticides aimed at adult fly populations. Sprays may be safely used in non-manure areas where flies congregate, such as rafters in the evenings, fence rails and barn sides in the morning sunshine and shady places in the heat of the day. In addition, sprays and wipes may be used on the animals themselves. Chemical baits can help eliminate the adult fly population. Applying poisons to the breeding habitat does more harm than good, as fly parasites and other beneficial organisms are thus destroyed.

Fly control should be preventative. It is much easier to prevent a buildup of flies than it is to get rid of them. Starting a biological control program as early in the spring as possible is a very important part of an "Integrated Fly Management Program".

Sources:

The Source -- BioLOGICAL Fly Control
P.O. Box 491703
Redding, CA 96049-1703
(800) 380-3560 (530) 243-8547 Fax (530) 241-7848
info@sourcebiofly.com

BICONET
5116 Williamsburg Rd, Brentwood, Tennessee 37027
info@biconet.com
(800) 441-BUGS / Tel: (615) 370-4301 / Fax: (615) 370-0662

Spalding Laboratories
760 Printz Road
Arroyo Grande, CA 93420
1-888-880-1579
Fax: 1-866-738-9632

Joe