NORTH CAROLINA — Beneath North Carolina’s vibrant blueberry fields, a hidden pest poses a long-term threat. Scientists are now working to uncover its secrets and protect the state’s valuable crops.
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For North Carolina’s multi-million blueberry industry, a new threat is emerging: the prionus beetle. The long-lived larvae of this pest burrow into blueberry roots, slowly killing plants over several years and turning productive fields barren.
While the beetles are known to affect various crops nationwide, a monitoring program in effect for two years now has confirmed prionus beetles have migrated to Pender, Bladen, and Sampson counties, the heart of North Carolina’s blueberry production. The three counties account for 90% of the state’s highbush production, contributing nearly $120 million to the economy in 2023.
The blueberry crop is also celebrated annually in Burgaw at the North Carolina Blueberry Festival, taking place this weekend, June 20 -21. Festivalgoers can join N.C. State professors for a special guided tour of the N.C. State Horticultural Crops Research Station to gain insight into blueberry cultivation, production, and the industry’s ongoing challenges and triumphs.
One of the professors, Lorena Lopez, and her team at N.C. State, will be there. Lopez and partners started a monitoring program in 2024 to understand the prionus beetle’s elusive life cycle and develop urgently needed management strategies before it decimates more of the state’s blueberry fields. In the last two years, more than 100 acres of blueberry plants were infested, the study found.
However, the true extent of the prionus beetle infestation across North Carolina isn’t known. This is because damage occurs out of sight, within roots and branches. Although difficult to pin down, it becomes noticeable only when plants show significant decline, typically through symptoms like dead branches, wilting, or if they can easily be pushed over due to hollow roots. By then, it’s too late to save the crop.
Lopez has worked with more than six farmers across Pender, Bladen, and Sampson counties to see first-hand the extent of the beetle’s reach. Her work also extends to advising other growers who worry about the beetle’s potential impact on their crops.
“This is a slow killer, it could stay multiple years in their roots and these beetles are not moving from plant to plant,” Lopez explained. “They go into one plant, and they stay there their entire life as a larva. So they could come and destroy an entire field, but it’s gonna take time.”
So, what are prionus beetles?
Root-boring longhorn beetles, the prionus is generally reddish-brown to black in color. Adults typically range from about 1 to 3 inches and are characterized by their distinctive, long, saw-like or deeply notched antennae. However, the larvae are large, creamy white to pale yellow and cause the most significant damage. The legless grubs can grow up to 3-to-4-inches long, equipped with a small head and powerful chewing mandibles.
Adult females only survive for about 10 to 20 days and can lay hundreds of eggs in the soil around blueberry plants. Once hatched, tiny larvae immediately burrow to feed on the plant’s roots. As they grow, they tunnel deeper, munching away for an unusually long three-to-five years by creating extensive tunnels to essentially choke off the plant. This prevents water and nutrients from reaching the rest of the bush and leads to gradual decline and death.
The unusually long larval stage is uncommon among insects, making the pest resilient and challenging to study and control.
Lopez’s monitoring study is funded by the North Carolina Blueberry Council. To further expand her research and ensure future access to pest management tools for specialty crop farmers, including blueberry growers, Lopez has applied for additional funding from the IR-4 Project, an initiative headquartered at N.C. State and funded by the U.S. Department of Agriculture.
“We want to identify all of these different gaps in our knowledge about their biology and their behavior in order to come up with some emergency treatments,” Lopez explained. “We still want to know how many we have in these fields and exactly which fields are infested.”
The team utilizes pheromone traps — combining female prionus pheromone lures with panel and pitfall traps — which are crucial for attracting male beetles and pinpointing their peak activity periods.
Only blueberry roots with active feeding larvae are a definitive indication of a blueberry infestation. The presence of adult prionus beetles in blueberry fields or captured in monitoring traps don’t necessarily mean the field itself is infested. This is because prionus adults are strong flyers, capable of traveling long distances from nearby forest areas where they also feed on hardwood trees.
In 2024, data from mid-June to late July showed significant adult catches across commercial farms and research stations, particularly in Bladen (735 adults) and New Hanover (49 adults) counties. Forsyth County, while monitored, showed minimal activity with only one adult.
The 2025 season has revealed surprisingly early activity. Since traps were set in the first week of April, adult prionus beetles emerged from blueberry fields in five of six monitored locations, including Pender, Bladen, New Hanover, and Forsyth. Only the N.C. State Horticultural Crops Research Station in Castle Hayne has yet to record adult emergence during this early period.
Anna Moore Hoy, food safety coordinator for Ivanhoe Farms, a participant in the research, highlighted the challenges growers face firsthand.
“The problem with the beetle is it is hard to identify if you’ve actually had them until after they’ve left,” she said. “We’ve had some issues with some plants, but right now they’re in season, so after that we’re going to try to determine if the beetle is what caused them to die or what happened to them.”
Moore Hoy confirmed Ivanhoe Farms has been in frequent communication with N.C. State researchers to get to the root of the problem. While the beetle hasn’t presented itself as a widespread issue for their farm yet, they are actively participating in the monitoring program.
“We’re going to be looking into some of the bushes that have died and submit them to the research to see if it was killed by the beetle,” Moore Hoy said.
Since the beetles affect the plant, namely the roots, they don’t pose a threat for the blueberry fruit itself or to human health. Fruit can still grow from the plant even if larvae are feeding on its roots. Only when the plant is killed by the beetle will fruit stop being produced.
Though traditional literature has indicated destructive larvae attach to roots, Lopez’s team also found they’re not limited to roots as previously thought.
“We’re finding larvae in branches up to 4 feet tall, that makes it harder for us to manage them,” she said.
As Lopez explained, if larvae were confined to roots, treatments might be applied to the soil, but it’s not as easy when the beetles are scattered in branches. While it can be clear the beetles are in the roots after a plant dies, finding them in branches requires careful dedication to each plant.
Lopez added visible symptoms in blueberries can be elusive and often misleading: “We still don’t know yet what the clear signs of infestation are.”
The beetles have posed challenges across the country for at least 10 years, with the root-boring pests found to cause significant damage to different woody plants.
For example, out west the California prionus harms nut trees like pecans, as well as cherries, peaches, apricots, and hops. East, other prionus species feed on trees like apple, oak, poplar, linden, and pecan.
Lopez admitted the exact reasons these beetles began feeding on blueberries remain unclear. While the problem was first reported more than a decade ago, she said the “severity of infestations” continues cropping up.
Unlike apple trees where specific symptoms like branch die-off or yellowing leaves often point directly to prionus, these same signs can come from the old age of blueberry plants or other factors, such as drought stress or disease.
“Growers may think that many of their plants are senescent,” Lopez said, meaning naturally aging and dying, “but actually these beetles have been in there killing their plants.”
By the time visible symptoms like wilting or plant decline appear, the damage is extensive and irreparable.
“So far, we can only find out if a field is infected because the plant roots are hollowed and are all eaten up. It’s a shame,” Lopez said. “By the time we find the larvae in people’s plants, it’s pretty much dead or unable to recover.”
Managing prionus beetles in crops
Currently, there are no registered insecticides specifically for prionus beetles in blueberries, and their deep, multi-year feeding makes applying traditional treatments challenging. Unlike other blueberry pests, like the stem borer or flatheaded borer that feed on bushes for only weeks, prionus grubs are much more steadfast.
“What my lab will develop is biology and behavior knowledge,” Lopez said, explaining the data they collect will pave the way for testing control methods.
Her team aims to begin trying out techniques using the already available lure as early as next year. Potential strategies include mating disruption — flooding the air with pheromones to confuse males and prevent reproduction — and mass trapping. Both methods, however, present cost considerations.
“Mass trapping may be expensive. Mating disruption may be expensive, too, because we will need a bunch of lures,” Lopez explained.
Beyond behavioral tactics, chemical control remains a potential avenue, but with other obstacles. Contingent on funding, Lopez intends to begin insecticide trials in both lab and field, targeting live larvae. She noted existing pesticides, tested on other prionus species, have often proven ineffective against large larvae, highlighting the need to target smaller ones.
Ultimately, Lopez said the most promising approach will likely be multifaceted — an integration of techniques her team will assess.
“It’s going to take time, and while we might slowly see a ‘freeze’ in populations, measuring that success will be difficult, requiring new development,” Lopez said.
Addressing a hidden threat like the prionus beetle requires more than just scientific research; it demands close collaboration with the growers directly impacted. This includes them contacting Lopez often for infestation verification — a partnership vital to research, she said, as it provides real-world data and access to affected fields.
Lopez cited an example of a grower, who remained unnamed due to the confidential nature of the study. The person purchased a farm, only to discover prionus beetles were running rampant.
“It turns out a lot of his plants are dying due to that beetle,” Lopez revealed. “That’s very frustrating to see those kinds of situations.”
Yet, it resulted in a proactive collaborator, forging a strong partnership to protect his fields, she added.
“There’s many that are concerned, but are also willing to work together to find a way to solve this issue or mitigate whatever is happening out there,” she said.
Even as North Carolina’s blueberry harvest season concludes in June, the monitoring study will continue throughout the year. The program is actively tracking adult beetle emergence until October and monitoring larvae until November. Blueberry farmers with concerns about a potential infestation can reach Lopez via email at llopezq@ncsu.edu or learn more about the study here.
“We have a lot of work to do for the next five and 10 years,” Lopez said.
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