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Boxler encourages producers to remain vigilant about fly control in cattle

by Wyoming Livestock Roundup

It is never too early to check into the best method of fly control for cattle grazing this summer. Producers who fail to provide adequate horn fly control for their cattle could be giving up between four and 15 percent of their weaning weight, according to David Boxler, entomologist with the West Central Research and Extension Center. In addition, if the cattle are grazing in an area with stable flies, the calves could be losing up to one-half pound of gain a day. 

Fly control is important and can be a successful management tool if used correctly, Boxler said. There are many types of fly control on the market, and producers need to evaluate their management style, when their cattle go to grass and how much access they have to the animal once it goes to grass to determine which method of fly control to use.

Methods of control

Feed additive, such as ClariFly Larvicide, disrupts the development of horn fly and face fly larvae in the manure of treated cattle. 

The product can be purchased in mineral or as a block from participating livestock feed centers. ClariFly is an insect growth regulator (IGR), which means the animal has to intake that product on a regular basis through the season for it to work, Boxler explained. 

“If they aren’t eating the material, chances are you aren’t getting maximum control,” he said.

Fly control tags like the XP 820 provide about 14 weeks of good fly control, which is about as good as can be expected, Boxler said. 

“When producers brand in May, they like to apply the tag then, but there are very few flies,” he explained. “What happens is the tag is releasing product, but the producer is getting very little benefit from it.”

The problem with fly ear tags is most producers want to apply a control product before they turn the animals out to grass and not deal with the animals the rest of the summer, Boxler said. 

“If producers want to use a fly tag, I recommend they wait until as close to June 1 as they can to get the greatest degree of control throughout the summer,” he explained. “The longer you can postpone ear tagging, the greater degree of control you’ll have toward the end of summer. You cannot tag in early May and expect the tag to last all summer.”

“Our studies have indicated to get the most dollar from your investment, the tag needs to be applied around June 1,” he stated. “Normally, you will start to see an increase in horn flies around the last week of May. Horn flies will be around until mid-September, and maybe even later if we don’t see a frost.”

“We could see horn fly numbers through the end of September if the weather is mild,” he added.

Boxler said scientists continue to pursue research of a slow release fly tag system, but the technology hasn’t been completely developed and is very expensive. 

In the meantime, producers need to consider rotating through the different classes of fly tags on an annual basis to prevent the flies from building up  resistance to the fly control currently available. Three classes of fly tags are currently on the market – organophosphates, synthetic pyrethroids, and Abamectin, a macrocyclic lactone. 

Stable fly threat

Not only do producers battle horn flies and face flies, but stable flies are also becoming more of a threat in some areas. 

“Fly tags aren’t totally effective in reducing stable flies,” Boxler said. “Because of that, we have been focusing our research on developing an effective treatment method for stable flies.”

Currently, Boxler recommends treatment by spraying the affected animals with a mist blower sprayer or power sprayer. 

“We have found it will reduce the stable fly numbers by 72 percent, if it is done correctly,” he explained. “It needs to be reapplied once a week throughout the fly season.”

A mist blower sprayer can be mounted in a pickup bed or on flatbed. When a producer is refilling salt and mineral or checking on windmills weekly, they can use the mist sprayer on the cattle at that time. 

“This has become a popular method of controlling stable flies by some livestock producers in the Nebraska Sandhills,” Boxler said. “In addition, this type of spray methodology is also very effective for reducing horn flies and face flies.”

The downside of the mist sprayer is the initial cost, Boxler continued. 

“The average cost of a mist blower sprayer is around $6,500,” he said. “However, if you treat it right, it could last 10 to 15 years.” 

“You can also use it to spray weeds in the pasture,” he added. 

The sprayer can be cleaned with a mixture of 10 percent ammonium and water flushed through the system, which will neutralize any products in the sprayer. 

Evaluating fly control 

Producers should check their cattle between eight and 11 in the morning to evaluate whether their fly control is working. 

“Look for horn flies on the sides and backs of your cattle,” Boxler explained. “If there are enough flies to cover a couple silver dollars, you may want to reevaluate the fly control method you are using.” 

“A couple silver dollars are the equivalent of a couple hundred horn flies. Two hundred horn flies per animal is considered to be the economic injury level,” he added.

Boxler said morning is the best time to evaluate horn fly control because flies will be resting on the top and sides of the cattle. As temperatures increase, horn flies move downward to the belly region of an animal where they remain until daytime temperatures fall, he explained.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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