By Carolyn Bernhardt
July 31, 2026
Cut it down. Spray it. Pull the seedlings—and buckthorn still finds a way to return. For decades, land managers have thrown nearly every tool they have at the tenacious invasive: removal, herbicides, planting native seed mixes, and sometimes even goat grazing.
Common buckthorn (Rhamnus cathartica) has been a priority species for MITPPC since its first year of operation in 2015. Since then, various teams of researchers have discovered much about the plant’s ability to regrow, and which tools work best over the long term. Even so, they have long suspected that an effective biological control option would help target buckthorn more precisely, complement existing management approaches, and reduce herbicide use.
Currently, two MITPPC-funded projects are focused on determining whether naturally occurring fungi could serve as a precise, effective management tool. Since both projects began, researchers have made important progress in understanding which fungi attack buckthorn and how they might be used safely to help manage the invasive plant.
Familiar fungus, new potential
“The use of a rust fungus as a biocontrol agent for invasive species can be a controversial topic,” says Jyoti Saini Sharma, PhD, a researcher in the Olivera Firpo Lab. Introducing a pathogen to the landscape can make many people wary, and reasonably so. But, Sharma says, “Our approach takes advantage of a crown rust species that is already present and widely distributed across the state.” The fungal species infects two highly invasive plants—smooth brome and buckthorn—which Sharma says could become an additional tool for managing buckthorn.
When the lab’s funding began in 2023, the team collected rust-infected buckthorn from around the state. They used Nanopore sequencing to identify them—a process Sharma says offers a “fingerprint” of each fungal species. The team ultimately identified six species of the crown rust complex infecting buckthorn in Minnesota, two of them observed for the first time. The team observed that over 80% of the samples analyzed corresponded to Puccinia coronati-brevispora, the crown rust pathogen that infects smooth brome.
In 2025, the team conducted field trials to evaluate the effects of P. coronati-brevispora on buckthorn seedling biomass and mortality. They saw unexpectedly high levels of seedling mortality and sharply reduced plant growth. “We observed that inoculations conducted in May-June using a 20% straw coverage resulted in an 80-90% reduction in total biomass and leaf area, 50% reduction in plant height, and 65% seedling mortality relative to uninoculated controls,” Sharma says. The team is repeating the same experiment this year.
Sharma shares that “In the future, we intend to partner with land restoration institutions and managers to evaluate this control approach in other natural settings and gain insights into its applicability in land restoration.”
Balancing promise with precaution
Meanwhile, the Robert Blanchette lab has also been hard at work investigating native canker, wilt, and root pathogenic fungi as possible biological controls for invasive trees in Minnesota. Since 2023, the lab has been among the first to explore the concept. “Nick Rajtar and Robert Blanchette's preliminary work sparked the idea,” says PhD candidate Ryan Franke, who now works in the lab. “Although none of the fungi initially identified as possible agents of biocontrol are still being considered, their work was the springboard for the work we are doing now.”
So far, this team has collected fungi associated with dying buckthorn from 20 different sites around Minnesota and Wisconsin. They recorded an average common buckthorn mortality rate of 90% just 11 months after cut stumps were treated with the fungus Chondrostereum purpureum. “We predict that the mortality rate will increase over the next year to greater than 95%,” Franke says.
According to him, the fungus is a generalist pathogen with a wide host range. “Future research needs to identify the environmental fate of C. purpureum where it has been used as a mycoherbicide to kill buckthorn,” he says. Once this fungus has killed a buckthorn stump, it will produce spores from fruiting bodies on the stump for a year or two. Researchers want to confirm that using the fungus is unlikely to infect nearby non-target trees through fresh branch wounds. “One study in Canada found that a strain of C. purpureum that was used to kill red alder stumps did not spread to surrounding vegetation,” Franke says. “We hope to corroborate this finding by conducting a similar study here in Minnesota.”
Growing the field
MITPPC funding has helped build the scientific foundation of buckthorn management. Both Franke and Sharma say it has also accelerated their professional development.
For Franke, that has meant the opportunity to more deeply understand the research process. The experience, he says, has directly fed into new research directions, including a proposal he developed with an advisor to design a mycoherbicide for black locust. “I look forward to taking this expansive toolkit with me as I advance in my career post-graduation,” he says.
As a researcher, Sharma has felt the impact of MITPPC-supported work in broadening her capacity, particularly by providing opportunities to build her molecular and field survey skills. Now, she says, these skills help her pursue previously unanswered questions in invasive species ecology, such as detecting and confirming hybrid buckthorn and comparing rust infection severity and diversity relative to common buckthorn.
Beyond individual skill-building, the collaborative nature of MITPPC-funded research has further expanded the scope and reach of this work, connecting Sharma and Franke with researchers at the USDA-ARS Cereal Disease Laboratory, as well as the Minnesota Department of Agriculture, the Minnesota Department of Natural Resources, the Wisconsin Department of Natural Resources, Friends of the Mississippi River, and various citizen scientists.
As MITPPC-supported research continues to refine tools and partnerships for invasive species management, research on buckthorn now points toward a different kind of intervention—one that harnesses biological systems already present in the landscape to target invasive species. As Franke puts it: “It's a matter of finding fungi that are capable of causing a relatively quick onset of systemic and fatal disease in their respective hosts and finding the best methods to apply them.”
The Minnesota Invasive Terrestrial Plants and Pests Center research is supported by the Environment and Natural Resources Trust Fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources.
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More information
- Effects of Puccinia species complex on common buckthorn, research project
- Biological control of buckthorn using fungi, research project
- Fungi Associated with Dying Buckthorn in North America (Forests, 2025)