Photo courtesy of USDA ARS

Integrated Pest Management for Fly Control 
in Maine Dairy Barns
Prepared by Patricia Westenbroek, Extension integrated farm educator

Noticed a few flies around? A silly question, perhaps, about a serious issue. Flies around the barn and milking parlor are a nuisance to the cows and to us. How can we manage the level of flies in our dairy operations? A multi-pronged approach, called Integrated Pest Management (IPM), is the key.

The first step in every IPM program is to learn about the pests that are causing the problem. On dairy farms, the primary fly perpetrators are the housefly and the stable fly.

The housefly (Musca domestica) is the most common and costly fly pest. The life cycle of the housefly can be completed in 10 days during warm weather. In a few more days, an adult fly will emerge to mate and start the next generation. Since each female housefly lays 150–200 eggs, and one pound of manure can contain more than 1,500 maggots, it is important to take steps to break the life cycle.

Stable flies (Stomoxys calcitrans) are similar in appearance and lifestyle to houseflies, with one important distinction—they bite! Like the housefly, the stable fly enjoys a moist, decaying environment. Since this is a blood-feeding fly, its economic impact can be large. Stable fly populations can lower milk production by 15 to 30 percent!

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Housefly	Stable fly		Fly life cycle
		Images courtesy of  Cornell University

• Determine current levels of fly populations: for instance, you could put up fly strips and record the frequency with which they need replacing. You need to know your starting point in order to track your progress.

• Identify an achievable goal: decide the level of flies you can live with (for instance, a low enough population level that strips only need replacing once a week).

• Map out a way to get there: develop an IPM plan for keeping fly populations below unacceptable levels. Your plan should include elements of each of the four control categories described below.

• Act early! Fly populations start building when the weather warms up, so begin your fly control program in early spring.

• Track and evaluate your progress. Use sticky tapes or speck cards to monitor fly activity in and around barns and the milking parlor. Keep records of how fast they fill up. Record any control actions you take, and when they were taken. Evaluate what worked and why.

The biggest part of cultural fly control is sanitation. Good sanitation is the most practical and economical way to manage fly populations. It’s best to begin before the flies have had a chance to develop into large populations.

• Keep open feeding lanes and the concrete corners of the feeding bins clean.

• Clean out calf hutches and holding pens on a regular basis and keep them ventilated. Move portable hutches on a regular basis and elevate one of the sides to provide extra ventilation if necessary. Calf areas are prime spots for fly breeding.

• Completely clean the entrance and exit lanes of the milking parlor daily, or after each milking.

• In liquid manure pits, prevent floating mats by collecting debris from the runoff collection channels, sediment basins and retention ponds.

• Get out your weed whacker and mower! Keep the entrance and exit walkway corners weed-free and trimmed to allow weekly cleanup of collected manure. Keep vegetation around barns, feeders, hutches, and manure piles mowed to eliminate fly resting areas.

• Remove small piles of manure and spread out straw as frequently as possible.

• Dispose of mortalities and afterbirth immediately.

• Keep animal areas as dry as possible. Scrape out manure regularly, and provide a three to four percent slope to allow drainage of liquid from stalls.

• Clean hard to reach areas such as behind waterers, in corners and under pen partitions.

• Clean the manure spreader when not in use: it’s an ideal place for flies to breed and be transported.

• Keep areas around feed storage, feed bunks and watering tanks free from moisture and manure. Fix water leaks promptly.

• Move your round bale feeder regularly to prevent manure, urine, and hay buildup.

• Keep flies out of milk rooms by maintaining window screens (use 14–16 mesh) and keeping doors closed whenever possible.

Biological Control

Nature can help in the battle against flies by providing natural enemies. These include predatory beetles and mites, parasitic wasps, and fly pathogens. You can promote natural enemies by keeping facilities clean and dry, and limiting pesticide use.

Predators: Hister beetles occur primarily in older manure packs. These small, black, shiny beetles consume up to fly 24 eggs a day. Predatory mites also feed on housefly eggs as well as small maggots.

Parasites: Parasitic wasps look like tiny gnats. Although they are harmless to humans and cattle and go unnoticed in dairy operations, they effectively find and kill fly pupae. The life cycle of most wasps is about 3 weeks long. There are wasps commercially available for release to augment the natural populations that exist.

When using biological control, remember that it is only one piece of a complete fly management program and, like many other components, will not eradicate flies entirely when used alone. Integrated pest management is a multi-method approach.

	Tips for Using Parasites If using parasites, find a reputable supplier, and ask specifically for Northeast-adapted strains. Research and experience have shown that the wasp species Muscidfurax raptor is most effective in northeastern dairy operations.   Photo courtesy of Cornell University Muscidfurax raptor Follow the directions provided by the supplier. Ask questions of your supplier to ensure that you are getting a high quality and suitable product shipped and delivered in a timely and dependable manner.  Don’t forget that these are living organisms—make sure the package isn’t left in the heat or cold—and release the wasps as soon as possible. It is best to begin releases in the early spring to establish the species and get a head start on the fly population. Parasites perform best in enclosed environments like calf hutches; their benefit is less noticeable in open environments.
Photo courtesy of Cornell University Flies on waterer

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Chemical Control

There are a wide variety of chemicals to control flies. Before using any chemical, always check with the Maine Board of Pesticide Control* to see if it is registered for use in this state and what regulations pertain to its use. Always follow the label’s instructions.

There are chemical controls for organic producers too. These chemicals such as pyrethrins and citric acid are naturally derived from plant materials. Contact Maine Organic Farmers and Gardeners Association (MOFGA)** for information. Before using any spray on an organic farm, contact both MOFGA and the Board of Pesticide Control.

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* Maine Board of Pesticide Control: Augusta 207-287-2731; Presque Isle 207- 764-2039 TDD: 207-287-4470

** Maine Organic Farmers and Gardeners Association: 207-548-4142