Developing better blueberry varieties is only part of the work needed to keep North Carolina’s blueberry industry thriving. Protecting those plants from diseases, and helping growers respond when new threats emerge, is just as important.
That work falls to researchers like Bill Cline and Caleb Bollenbacher, Extension plant pathologists with North Carolina State University based at the Horticultural Crops Research Station in Castle Hayne.
“Our work is a combination of research and extension,” Cline said. “On the research side, we investigate diseases of small fruit crops, especially those that affect blueberries. In our Extension role, we develop recommendations for disease management and deliver those recommendations to growers through meetings, publications and field days.”
Their responsibilities extend beyond plant diseases. They also advise growers on blueberry production practices ranging from cultivar selection and irrigation to freeze protection, pruning, harvesting and post-harvest handling. Much of that work centers on the Horticultural Crops Research Station, where most of North Carolina’s blueberry research takes place.
“The research station at Castle Hayne plays a key role,” Cline said. “That’s where most of the blueberry research is conducted, and where field days and farm tours are held. John Garner and his team do an excellent job managing the 50-acre blueberry tract there.”
While Cline and Bollenbacher’s work spans many aspects of blueberry production, several ongoing research projects highlight how they help the industry stay ahead of both long-standing and emerging disease challenges.
Solving yesterday’s problems
Blueberry diseases have shaped research in North Carolina for decades. Commercial blueberry production began in New Jersey before expanding south, but growers quickly discovered that North Carolina’s warmer, more humid climate brought new challenges.
“They found out a couple of things pretty quickly,” Cline said. “One was that there’s a lot more disease pressure in the hot, humid South. They also found out that their New Jersey cultivars weren’t happy here because they didn’t get enough winter chilling.”
That led researchers to pursue two goals simultaneously: developing blueberry varieties adapted to North Carolina’s climate while also improving their resistance to diseases. (The variety breeding was covered in a previous blog at https://blog.ncagr.gov/2026/07/15/15-years-in-the-making-each-new-blueberry-variety-comes-from-research-aimed-at-north-carolinas-future/)
“Over the years, we have repeatedly released blueberry cultivars that do well here, that are resistant to diseases, and that is the foundation of the blueberry industry here — climate-adapted, disease-resistant cultivars,” Cline said.
There are some chronic fungal pathogens that Cline says have been ongoing issues over the years. One of the biggest historical challenges was blueberry stem canker, a fungal disease that attacks the plant’s canes or branches.
“It cuts off the vascular system in the cane of the plant,” Cline explained. “The top of the plant dies, and so it really shortens the life of the plant.”
Researchers spent years evaluating breeding material for resistance. They would take seedlings of selected cultivare and inoculate them with the fungus that caused stem canker. That helped them find cultivars with resistance to that fungus. Today, thanks to decades of breeding and improvements in production practices such as irrigation, stem canker is far less problematic than it once was.
“We’ve sort of pushed past that now,” Cline said. “A lot of our breeding material now is canker-resistant. We’ve stopped doing a lot of the screening because we feel like we’ve gotten a handle on stem canker management.”
Preparing for tomorrow’s threats
As one disease becomes more manageable, another often emerges. Today, one of the team’s biggest concerns is bacterial wilt, a disease already causing significant losses in parts of Georgia and Florida and now confirmed in North Carolina.
“We have done our first report of that disease in North Carolina,” Cline said. “So we’re turning our attention to bacterial wilt as a new disease of concern.”
The disease spreads through the soil and blocks the plant’s vascular tissue, eventually causing rapid wilting and death.
“It causes a rapid wilt,” Cline said. “The bacterium blocks the vascular tissue in the plant and chokes it off. So you see blackening of the stems and an area in the field where the plant death is spreading in a patch – everything is dead in the center, and they’re dying at the edges, further and further out, over time.”
Because bacterial wilt is difficult to eliminate once it becomes established in a field, researchers are focusing on identifying tolerant varieties, which is one of the most effective long-term management strategies. So far, they know many Florida blueberries are affected, but different blueberries grow in that state.
“We have an experimental plot on a farm where we’ve detected bacterial wilt,” Cline said. “We don’t know how our varieties – our cultivars – grown in North Carolina react to this pathogen. So, this is an opportunity to go to a field that has an infested soil and plant as many North Carolina cultivars as we can and see how they withstand the disease.”
The researchers face a challenge in studying the bacterial wilt because it’s a soil-born pathogen that they don’t want to spread. So they don’t want to take it anywhere such as the research station. Instead, they’re sticking to that on-farm plot where the grower has agreed to allow them access. The information they gather there will help growers decide what to plant if bacterial wilt becomes more widespread.
“This is really important from a management perspective,” Bollenbacher said. “Your first line of defense is cultivar tolerance. This is a disease that can be very difficult to control chemically or with other methods because once it’s in the soil, it’s very difficult to get rid of. If we discover it’s a problem here [for currently grown varieties] and can find varieties that are resistant or tolerant, that’s going to be our first line of defense and our best management practice.”
Staying ahead of changing diseases
Not every research project focuses on a newly discovered disease though. Bollenbacher is also studying anthracnose fruit rot, a disease that has affected blueberries for years but is becoming a greater concern because of reports of fungicide resistance elsewhere in the Southeast. [Note: anthracnose fruit rot is caused by fungus and should not be confused with anthrax, which involves bacterial spores. While anthracnose causes problems for small fruits, it is not dangerous to humans.]
“We want to get ahead of the curve here and see what we have, since it hasn’t been done already,” Bollenbacher said. “Do we have resistance in the population we have here for anthracnose? And what chemicals and other management practices do we have that can get around that potential resistance and get better control for it?”
Bollenbacher’s work is exploring old and new fungicide chemistries to see how effective they are in North Carolina. He is using the fungicides on blueberry plants in the field to see how they work there, and he’s also testing them in the laboratory to see how the fungus responds under controlled conditions. The isolated lab work forces the pathogen – the anthracnose fungus – to interact with the fungicide active ingredients, and that helps researchers see just how resistant the anthracnose fungus is to each fungicide.
“The field can have so many factors that affect how well these chemistries work,” Bollenbacher said. “We might see something that doesn’t work in the field, and we want to know why. Is it because that chemistry just has an issue in its application method – it’s not very effective in the field? Or is there actual resistance within the pathogen?”
That approach also reflects the evolution of the program itself. Cline, who has worked at Castle Hayne since 1987, said bringing Bollenbacher onto the team before his retirement helps ensure continuity while expanding the program’s capabilities.
“He has some molecular expertise that I don’t have,” Cline said. “It’s exciting to have a new skill set. We’ve got all sorts of questions that Caleb will be able to answer in the future.”
From research plots to growers’ fields
Research is only part of the team’s mission. Getting that information into growers’ hands is equally important.
“We do a blueberry management guide every year, a regional management guide at SmallFruits.org and just really try to have the resources out there for growers,” Cline said.
The team also publishes disease guides, hosts field days and organizes North Carolina’s annual blueberry meeting, where growers hear the latest research findings firsthand.
Just as importantly, they work closely with county Extension agents and NCDA&CS agronomists, who are often the first to identify new issues in growers’ fields.
“They’re part of the rapport with the growers,” Cline said. “Very often we’ll get a report of a problem that we have no idea about because an agronomist has seen it and we haven’t. They’re a link to the growers, just as the county agents are.”
Those partnerships help researchers identify emerging problems quickly and ensure new recommendations reach growers just as fast. For Cline, that ongoing cycle of research and outreach has helped shape North Carolina’s blueberry industry for decades.
“There have been tremendous impacts over the years,” he said. “I think about things like overhead irrigation for freeze protection that was developed in response to crop losses from freezes. You can save a blueberry crop and pay for that irrigation system in a single night with the value of the crop.”
Whether confronting long-standing diseases like stem canker or preparing for emerging threats such as bacterial wilt and fungicide-resistant anthracnose, the work continues. As diseases evolve, so do the questions researchers are trying to answer. Likewise, the recommendations they provide evolve too to help North Carolina’s blueberry growers continue producing healthy, high-quality fruit.