Nebraska cattle producers are already dealing with drought and a historic wildfire season. Now, a UNL entomologist is warning them about another threat that has consistently been arriving ahead of schedule.
Dave Boxler, a Nebraska Extension livestock entomologist based in North Platte, says this year's unusually warm spring pushed horn fly populations to damaging levels weeks earlier than normal.
The longer season raises economic concerns for producers across the state. Horn flies begin causing measurable losses in cattle performance once populations reach around 200 flies per animal; a threshold known as the economic injury level, which Boxler said is typically reached in late May or early June in Nebraska.
"We were seeing horn fly numbers on cattle in mid-April that were exceeding the economic injury level of 200," Boxler said. "And that was all caused by the super warm temperatures that we were experiencing."
Boxler said the trend isn't new. He's observed the horn fly emerging earlier in the spring and maintaining higher populations in the fall for several years.
"We've seen that happening now over the last five to six years because of our warming conditions in the spring," Boxler said. "And then also we're seeing higher populations later in fall because of the warming in the fall, too."
According to Boxler's article, horn flies are considered the most economically damaging pasture pest in North America, with estimated annual losses exceeding $1 billion nationwide.
"If you have a population of 3,000 horn flies over, say, 90 days, you can lose a gallon of blood," Boxler said. "It's the stress of the animal trying to dislodge those flies that causes the weight loss."
With cattle prices at near-record highs, he said the economic stakes of poor fly management are higher than usual.
"Calf prices are extremely high right now," Boxler said. "So, the more pounds you can put on an animal, the greater the return."
The UNL extension educator said the horn fly has also been developing resistance to insecticides that producers in the state use. Boxler said ear tags, one of the more popular fly-control methods in Nebraska, are becoming less effective over time.
"We haven't had a lot of new products developed for 15 to 20 years," he said. "And that's why we're seeing more and more resistance issues, because we don't have different chemistries to rotate to."
Boxler said he recommends producers rotate between insecticide classes each season and remove ear tags at the end of the fly season. In addition, he emphasized the need for more producers to watch their animals for behavioral signs of fly stress.
"When you see an animal tossing its head 10 times in a minute, you've got some issues," Boxler said. "You need to provide some type of fly control."
Boxler said he will begin testing a new company-developed synthetic pour-on insecticide this June — the first new mode of action for horn fly control since 2016.