Effective fly control needs to start early

Parasites and insects can negatively impact dairy cattle performance and profitability. Now is the time to develop your strategy to limit their impact on your farm.

First, let’s briefly discuss mange and lice. These bothersome parasites are present year-round and build during cold weather. They are most often found on cattle necks, backs, hips and tailheads. Controlling these parasites enhances productivity primarily by improving cow comfort and the behaviors associated with it. Treat all cattle on the property at the same time if possible, choosing a time when they are not stressed or in poor condition. If groups must be treated separately, they should be kept apart to ensure no contact between treated and untreated groups. Treatment programs often contain a general endectocide to cover both external parasites, such as mange and lice, and internal parasites. Consult your veterinarian or herd health professional for specific recommendations.

Now on to flies, which are a nuisance to farm workers and animals, transmit disease and cause significant economic loss. Flies cause livestock to expend extra energy by fending them off instead of resting, eating 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, insecticides often were the sole strategy to manage flies in dairy and livestock barns, 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 and 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 houseflies, horn flies, stable flies and face flies. Houseflies are the most abundant around livestock operations but cause the least irritation. Both horn and stable flies are 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 housefly 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 10-12 hours, and the maggots move into the wet manure. Fly maggots mature in 4-5 days under warm, moist conditions. Pupation occurs in the drier parts of manure, with the adult flies emerging in 3-5 days. Although capable of movement up to several miles, houseflies normally stay within 0.5-0.75 miles of their breeding sites.

Sanitation

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. 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 an additive that can be added to calf and heifer feeds as well as feed for any adult cows in housing situations where manure accumulates over time. This generally starts in early to mid-April in most of the Midwest. IGRs 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. Diflubenzuron 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 before flies appear 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/trapping and larvicide feeding — will go a long way toward reducing fly populations and positively impacting productivity.

Barry Visser is a nutritionist for Vita Plus.