Controlling flies on dairy farms

    Now is the time to make fly control plans for your operation. Flies are a nuisance to farm workers and animals, transmit disease and cause significant economic loss. Flies cause livestock to expend extra energy fending them off instead of resting, feeding and milking. Fly control is critically important to all dairy operations to reduce the spread of disease and improve animal comfort, resulting in decreased stress and greater efficiency of growth or production.  
    In the past, management of flies in dairy and livestock barns often relied solely on insecticide use. But this single-tactic approach can aggravate fly populations’ resistance to insecticides and inadvertently destroy natural enemies of flies. Today, farms are successfully combining careful use of pesticides with other integrated pest management practices.

Fly identification, biology
    Identifying the type of flies on your dairy and understanding their lifecycle is key to developing an effective IPM plan. Common flies found on dairies include house flies, horn flies, stable flies and face flies. House flies are the most abundant around livestock operations but cause the least irritation. Horn and stable flies are both bloodsucking insects and can be very painful to their hosts. Although house and face flies don’t suck blood, they do spread disease.  
    According to Purdue University research, a fly can complete an entire generation – from egg to adult – within as few as 10 days. All flies pass through four life stages:  egg, larva (maggot), pupa and adult. During its lifecycle, which is about 30 days, a house fly female can lay up to 1,000 eggs. These eggs are deposited on moist manure or any type of moist, rotten or decaying organic matter. The eggs hatch in 10 to 12 hours, and the maggots move into the wet manure. Fly maggots mature in four to five days under warm, moist conditions. Pupation occurs in the drier parts of manure, with the adult flies emerging in three to five days. Although capable of movement up to several miles, house flies normally stay within one-half to three-quarter miles of their breeding sites.

    The largest economic return for fly control is effective cleanliness and sanitation. Approximately 90% of a dairy’s flies will develop in less than 10% of its physical area. Flies reproduce in undisturbed, damp organic matter. Removal and disposal of wasted feed, spilled milk or manure will go a long way in reducing fly populations. Eliminating tall weeds around facilities can reduce attractiveness to flies, especially stable flies. In some cases, alternative bedding sources (such as sand in calf hutches) can be considered during the summer months.

Feed an insect growth regulator
    The key to any fly management strategy is to start early in the season before fly populations become a problem. An insect growth regulator is a feed additive that can be added to calf and heifer feeds as well as any adult cows in housing situations that allow manure to accumulate over time. This generally starts in mid-April to early May in most of the Midwest. Insect growth regulators will not get rid of current flies but can go a long way in preventing future flies. Your nutritionist can assist with specific larvicide recommendations.         
    The larvicide diflubenzuron is the most common IGR used in dairy cattle and effectively prevents the four most-irritating flies from developing and emerging in the manure. Difluebenzuron breaks the fly lifecycle by inhibiting the synthesis of the bug’s body wall (exoskeleton), resulting in death before the larvae can become adult flies. Begin feeding diflubenzuron 30 days prior to flies appearing and continue until cold weather restricts fly activity in the fall.

Additional fly control strategies
    Residual premise spray is often beneficial throughout the summer to kill flies or deter other flies from coming into the dairy. Baiting or trapping flies is beneficial in certain locations. Large surface area fly control tape may aid in reducing the number of flies in confined spaces. Parasitic wasps have also been used effectively to help control the pest fly population. Lastly, don’t forget about pour-on fly control. This is perhaps the best option for controlling flies in a pasture situation. Resistance to chemicals is a concern; however, new products continue to come on the market.     
    Moderate to intense fly pressure can be stressful to dairy cattle in many ways and result in decreased profit. Flies are attracted to dairies due to the large amounts of feeding and breeding sites that exist on any operation. Cleanliness in these high-risk areas is a great place to start controlling flies, but this alone is not enough. Complementary fly control programs, such as spraying, baiting and trapping, and larvicide feeding, will go a long way to reducing fly populations and positively impacting productivity.  
    Barry Visser is a nutritionist for Vita Plus.


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