Controlling Horn Flies on Pastured Cattle

Cow with a high number of horn flies.
Cow with a high number of horn flies.
(Dave Boxler, University of Nebraska Extension)

Livestock producers will soon be sending cattle to summer pastures. Horn flies are a perennial pest of pastured cattle since their introduction from Europe in the 1880s. The horn fly spends most of its time on cattle, mainly on the animal’s backs, sides and when temperatures are very warm, on the belly region. Both sexes of horn fly feed on blood, averaging between 28 and 38 blood meals per day, with each blood meal lasting about 10 minutes. When horn fly numbers exceed 200 flies per animal, cattle will become more stressed due to fly biting. This stress reduces milk production in mother cows and grazing time, which leads to reduced weight gains. The annual economic losses caused by this fly have been estimated at $1billion in the United States. The fly has also has been implicated in causing summer mastitis. Horn fly numbers on Nebraska cattle can often exceed several thousand flies in late August or early September (Figure 1) .

Ear tag strips that have been utilized in past years, will not be available for the 2019 fly season. The strip is currently undergoing some design modifications. With most insecticide ear tags, it is strongly recommended to use two tags per adult animal for horn fly control. If face flies are present, apply one tag per calf. Delaying tagging until the last week of May or first week of June will provide the greatest impact on horn fly numbers through the fly season. Insecticide ear tags applied in late April or early May either need to be refreshed by mid-summer, or another fly control method implemented to insure season-long reduction in horn fly numbers.

Many horn fly populations in Nebraska exhibit some tolerance to synthetic pyrethroid insecticides. To manage fly tolerance issues, be sure to alternate insecticide classes of dusts, insecticide ear tags, animal sprays, pour-ons, and feedthroughs (IGRs). A list of delivery methods, labeled insecticides, and their Mode of Action (MoA) groups for horn fly control are found in Table 1. This includes organophosphates (Group 1B), pyrethroids and pyrethins (Group 3), avermectins and milbemycins (Group 6), juvenile hormone analogues (Group 7A), and benzolyureas –chitin inhibitors (Group 15). Continual use from a single MoA against a species can lead to resistance to all products in the group. To improve control, rotate between MoA groups during the fly season or at least annually.


Latest News

CAB Insider: Carcass Value Shifts, a Sign of the Times

Jan. fed cattle prices are normally choppy and we’re seeing that pattern in 2021. A primary difference, compared to 2020, is that last week’s average price is $14/cwt. lower, the same discount as the 5-year average.

18 min ago
U.S. President-elect Joe Biden is sworn in as the 46th U.S. President, at the U.S. Capitol in Washington, U.S., January 20, 2021.
Ag Industry Leaders Congratulate Biden, Echo His Call for Unity

Following the inauguration of President Joe Biden, the 46th President of the United States, agriculture industry leaders congratulated Biden and Vice President Kamala Harris.

3 hours ago
Black Ink: Valued Partners

Partnerships aren’t always about a 50/50 business arrangement or who gets what tasks, sometimes they’re simply about having a vested interest in somebody else’s success.

12 min ago
One former Secretary of Agriculture thinks a Biden Administration and USDA will focus more on crafting a farm bill that includes a focus on conservation.
Why a Biden Administration May Not Buy into the Green New Deal

As President Joe Biden took office Wednesday, one former Secretary of Agriculture thinks a Biden Administration and USDA will focus more on helping craft a farm bill that focuses on conservation.

2 hours ago
As wild pigs continue to expand out of control in Canada, the risk of wild pigs moving into the U.S. is very real. This is especially true for North Dakota and Montana, but given how mobile feral swine are, the risks are far beyond that, says Ryan Brook of the University of Saskatchewan. 
Canada Fights Back Against Out-of-Control Wild Pig Population

Wild pig populations in Canada continue to expand rapidly and are completely out of control in Saskatchewan, Manitoba and Alberta. A new tool may help control this invasive species. Here's why you should take note.

1 hour ago
Tyson Settles Anti-trust Case For $221.5 Million

Tyson Foods has agreed to pay a settlement of $221.5 million in the broiler chicken antitrust civil price-fixing lawsuit, according to filings Tuesday in federal court in Chicago.

40 min ago