Fly Management for Organic Dairies

Flies can decrease milk production and spread disease. In this article, Brad Heins, Extension Dairy Scientist with the University of Minnesota, looks at methods to control and management flies on organic dairies.
calendar icon 19 June 2012
clock icon 4 minute read

The spring grazing season is off to a quick start this year. Many cows were grazing in late March/early April. Here in Morris, the organic cows went to pasture May 3. The grass grew quickly in March; however, growth came to a halt with the cold weather in early April. During the last week of April one could hear the grass grow. We all need to manage the pastures properly so grass doesn't get out of control and we provide the maximum intake from pasture for cattle.

Along with the wonderful grazing weather and hot summer, come flies. One issue that is consistent among the farmers that I talk to is control of flies under organic conditions.

Horn flies, face flies, stable flies and house flies are all pests of dairy cattle. These flies can decrease milk production, reduce pasture feed intake, cause pinkeye, and may spread disease from one animal to another. Various studies have documented 10 to 30% reductions in milk production due to flies. One recent study estimated that stable flies may cause $1.3 million in annual losses for pastured cattle.

Two important blood sucking flies on grazing cattle in the Upper Midwest are the stable fly and the horn fly. Stable flies develop as maggots in a wide array of decomposing organic matter, including animal bedding and feed debris that accumulates wherever cattle are confined. Calf hutch bedding is a prominent source of stable flies around dairies. The choice of bedding material can minimize stable fly production; pine shavings and sawdust contained fewer flies than straw. Feed debris and manure that accumulate during winter are also important sources of stable flies, especially where overwintered debris piles remain intact into the following summer.

The horn fly is a second kind of biting fly that attacks cattle. They develop in undisturbed, fresh dung pats and nowhere else, so they are troublesome to organic herds on pasture. Horn fly control leads to increased milk production and calf growth.

Unlike other kinds of flies that just visit cattle for brief moments, adult horn flies reside on their host animals, making them especially vulnerable to control. Organic dairy farmers rely on essential oil repellents to alleviate horn fly problems, but success of these products is limited.

To combat horn flies, W.G. Bruce (a USDA entomologist), built a box in 1938 with one-way fly-screen baffles on its otherwise transparent sides and walked fly infested cattle through it to remove and capture their flies.

Bruce's simple design is now known as the Bruce walk-thru fly trap, and different versions have been studied for horn fly control in various parts of the country. Those studies showed that walk-thru traps can reduce horn fly burdens by 50 to 90%. Most recently, North Carolina State University replaced the side baffles with a system of blowers and vacuums, and this vacuum trap design will soon be manufactured and marketed by Spalding Labs as the Cow-Vac™.

Both traps are compatible with organic dairying, because a trap can be positioned at the entrance to a milking parlor, where cows come and go twice per day. Efficacy of any kind of trap will depend on the balance between the rate at which the flies are removed and killed by a trap and the rate at which the population naturally increases in the cows' pastures.

Sanitation should be the primary control option on any dairy. Because synthetic pesticides are not allowed on organic dairies, proper sanitation is of the utmost importance. Manure and feed provide the ideal habitat for house and stable fly production.

Manure and old feed should be removed daily, or at least twice a week, from calf pens, holding areas, feed areas and milking areas. To ensure success on the dairy, producers need to properly identify key pests, understand their biology and habitat, monitor their populations, and then reduce the fly population through mechanical or biological management techniques.

Ultimately, there are many tactics that producers can try out on their own farm. Suggestions include taking notes, evaluating how well things worked or not, and learning where to find additional answers to improve the well-being of cattle and reduce pests. In the future, my colleagues and I will be studying new strategies to alleviate pest problems.

June 2012

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