CALL TO THE BLUEBERRY COMMUNITY:

Developing effective management of Prionus species in blueberries requires a comprehensive understanding of their biology, regular monitoring, and integrated tactics. Thus, community-wide coordination is crucial for effectively diagnosing infestations and collecting information about this pest.

It is a good time to sample for Prionus beetles in blueberries! We encourage blueberry growers to inspect their blueberry fields for any signs of adult beetles emerging from the ground. These beetles usually emerge very close to the based of the blueberry plants. If you see these beetles on or near your blueberries, please contact the small fruit entomologist, Lorena Lopez, at llopezq@ncsu.edu to schedule a farm visit or talk details on how to sample blueberry roots to confirm or discard possible a Prionus infestation. Again, the presence of adult Prionus beetles in blueberry fields alone, doesn’t necessarily mean the blueberry field is infested. Only blueberry roots with feeding larvae are an indication of blueberry infestation.

Prionus longhorn beetles (Coleoptera: Cerambycidae) pose significant challenges in agricultural and forestry management in the U.S. due to their damaging larval stages. Species of Prionus beetles are woodborers and large-sized insects (2-3 in long, Fig. 1) that can devastate tree roots, impacting crop yields and forest health. In the last decade, Prionus beetles have emerged as a problem in the blueberry-producing region of North Carolina.

Fig. 1. Prionus adult female (top left), male (top right), and cocoon were larvae pupates and develop into adult (bottom).

To our knowledge, North Carolina is the first state in the country to have reported this pest feeding on blueberries. A focus of infestation has been detected in the heart of blueberry production in the intersection between Sampson, Pender, and Bladen Counties, NC, where more than 8,000 acres of this crop are grown. In this area, 100+ acres of blueberry plants have been confirmed as infested with Prionus larvae feeding on their roots and base of stems in the last two years (Lopez pers. comm.). Early detection is essential, yet current diagnostic methods are minimal, and control methods are limited. Infestations are reported when hundreds of plants start dying, and Prionus larvae are found in the roots, stems (Fig. 2), and/or soil at the time of plant removal. Prionus larvae can feed on the mature plants (5-15+ year-old-plants) for 3-5 years before emerging from the plants as adults (Lopez 2024).

Fig. 2. Advanced instar of Prionus beetle larva inside a blueberry root collected in Sampson county on April 28, 2025.

Severely damaged and infested plants usually show die-back of branches in early spring or wilting symptoms. Additionally, groups of multiple plants show these symptoms close by patches of forests, and plants are usually easily knock down by hand, indicating hollow or debilitated roots. When plants start showing these combination of symptoms, the plants are usually too damaged to recover. Currently, no other symptoms of infestations caused by these beetles, in addition to the ones mentioned above and plant death, have been identified. 

Despite the severe damage these beetles can caused to blueberries, there is little known about their biology when feeding on this crop, their emergence, mating, and oviposition periods. Therefore, a monitoring program was conducted during summer of 2024 and an extended monitoring program has started in 2025. The 2025 Prionus Monitoring Program will monitor adult emergence from April to October 2025 and monitor larvae from February November 2025, with the ultimate purpose of generating more knowledge related to the biology and ecology is this emerging pest of blueberries. This will be the first step to develop suitable management tools and inform pest management programs.

This year, two lured panel traps were place per location in six locations included in the monitoring program: two commercial blueberry farms without any reports of Prionus beetle infestation (in Pender and Bladen Counties), the Horticultural Crops Research Station in Castle Hayne (New Hanover County), and the three commercial farms with confirmed Prionus beetle infestation (two located in Sampson County and one in Pender), meaning adults have been observed within blueberry plantings AND larvae have been detected feeding directly on blueberry roots. Only blueberry roots with feeding larvae are an indication of blueberry infestation. The presence of adult Prionus beetles in blueberry fields alone, doesn’t necessarily mean the blueberry field is infested. The reason for that is that Prionus adults are can fly long distances and can move to the lured traps in blueberry fields from forest areas since they also feed on hardwood trees. More information about the beetles and the collecting methods can be found in the summary of the 2024 Prionus monitoring program.

This week, adults were observed emerging from cocoons made of soil particles nearby the blueberry plants in five of the monitored locations, in Pender and Sampson Counties (Fig. 3). Since the set up of the traps in the first week of April, we recorded the first emergence of Prionus beetle adults from blueberry fields in 2025 in five of six locations (no adults collected at the Research Station in Castle Hayne yet). Lured traps have collected 46 adult beetles from all locations since April 22. These upcoming weeks and increase on Prionus adult emergence is expected throughout summer. It was registered that after a few days with soil temperature above 70 ºF, adult emergence started (Fig. 4).

Fig. 4. Soil sensors were established at the 3 locations with confirmed Prionus infestations. Soil temperature and water content was measured to relate to Prionus adult emergence.

Acknowledgements:  We wish to thank Tiffanee Boone, Mark Seitz, Matt Strickland,  and Brad Hardison (Pender, Sampson, and Bladen County Extension agents, and John Gardner, the Horticultural Crops Research Station director) for their help servicing the traps at each location, Bill Cline for his contributions to this program, and the collaborating growers.

References

Lopez, L. (2024, July). The root of the problem: Prionus longhorn beetles in blueberries. NC State Extension. Retrieved from https://blueberries.ces.ncsu.edu/2024/07/the-root-of-the-problem-prionus-longhorn-beetles-in-blueberries/

North Carolina Small Fruit & Specialty Crop IPM. (2013, January). Prionus larvae found on blueberry. Retrieved from https://ncsmallfruitsipm.blogspot.com/2013/01/Prionus-larvae-found-on-blueberry.html

Oregon State University Extension. (2023). Pest alert: California root borer in hazelnuts. Retrieved from https://blogs.oregonstate.edu/hazelnuts/pest-alert-california-root-borer-in-hazelnuts/

University of Georgia Pecan Extension. (2016). Prionus Root Borers. Retrieved from https://site.extension.uga.edu/pecan/2016/06/Prionus-root-borers/

Utah State University Extension. (2010). Prionus Borers (Prionus californicus). Retrieved from https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1653&context=extension_curall