Beating the buckthorn blues

Mike Schuster and fellow researchers have opened up new avenues for controlling the invasive shrub.

Buckthorn branch with fruit

In the mid-19th century, North America imported two species of Eurasian buckthorn—common and glossy—because they made lovely ornamental hedges.

Big mistake.

head shot of Mike Schuster
Mike Schuster, Researcher, Department of Forest Resources

Today, its dense foliage and rapid growth help buckthorn, especially the common variety, crowd out native plants. The tall shrub has spread through forests, savannas, and towns in much of Minnesota and other states.

But it’s up against formidable foes like Mike Schuster, a researcher in the Department of Forest Resources. With his colleagues, he has opened up new avenues to controlling the green invader—and found some good news about its vulnerabilities.

For example, it had been thought since the 1990s that buckthorn seeds survived in soil for five or six years.

A couple standing outside
Steffanie and Matt Musich from Friends of Lake Nokomis volunteered to participate in Cover It Up "as a way to help advance the research around controlling buckthorn."

“We provided strong evidence that that was not based on data,” Schuster says. “We planted common buckthorn and observed it for up to four years. Across the 13,232 buckthorn seeds planted, germination occurred almost entirely in the first two years after planting. Therefore, the idea of a long-lived buckthorn seed bank was not realistic.”

Schuster’s work also showed that if buckthorn is replaced with fast-growing native species such as wild rye grasses, those plants will cover up and “shade out” much of the new buckthorn growth. Volunteers and professionals are putting this finding to use in many areas of the state through the U of M's Minnesota Invasive Terrestrial Plants and Pests Center’s Cover It Up project.

And to keep buckthorn stumps from resprouting, “We found that a herbicide not widely used, called fosamine, is really effective,” Schuster adds.

Horned heroes?

There’s one group that loves buckthorn: goats.

A recent study led by Tiffany Wolf, an assistant professor in the Department of Veterinary Population Medicine, and Daniel Larkin, an associate professor in the Department of Fisheries, Wildlife and Conservation Biology, probed the benefits of using goats to control buckthorn.

Goats readily graze on it, and work by Wolf’s former postdoctoral researcher Katie Marchetto showed that the animals didn’t spread the seeds. Marchetto discovered this by outfitting goats with diapers, feeding them buckthorn, and testing “what made it through.”

“Very few seeds—less than one percent—turned up in goat pellets,” Wolf says.

 Young woman holding a baby goat and kneeling next three more goats.
Former postdoctoral researcher Katie Marchetto working with goats.

Goats browsing in wooded areas are at risk of being infected, often fatally, by a brainworm carried by snails and slugs. But the three researchers were also part of a study showing that if waterfowl graze along with goats, they eat the snails and slugs and may lessen the risk to goats.

Unfortunately, goats also eat native plants. However, “Native and invasive species come back after grazing,” Wolf says.

"The bottom line is that while goats can play a role as part of a sustained, multi-pronged strategy for buckthorn control, they’re not a panacea," Larkin says.

Pop Quiz

How long do buckthorn seeds survive in the soil?

Expand all

A. 9-10 years

No, they're not that hardy.

Expand all

B. 5-6 years

No, but you're only a few years off.

Expand all

C. 1-2 years

Yes! U of M research showed that.

Can fungal infections kill buckthorn?

Fungi that attack buckthorn could provide another means of control.

In the laboratory of Robert Blanchette, a professor in the Department of Plant Pathology, graduate student Ryan Franke keeps a collection of candidate fungi, most taken from dead and dying buckthorn.

Franke grows each fungus on its own wood chip in the lab. When he has a big enough supply of a fungus, he takes it to a campus greenhouse and inoculates it into the bark of a young buckthorn to test its pathogenicity to the plant.

Results so far are promising.

Young man inoculating a buckthorn sapling.
Ryan Franke inoculates a young buckthorn with fungus.
Researcher cutting a sample of crown rust-infected buckthorn.
Pablo Olivera Firpo takes a sample of crown rust-infected buckthorn.

“We have some aggressive fungi,” Franke observes. And, Blanchette adds, “Once we get the best species [of fungus], we’ll work out the best application method.”

Also, Pablo Olivera Firpo, a research associate professor in the Department of Plant Pathology, leads a project to find which species of crown rust—a fungus that attacks oats, barley and turfgrass and also grows on buckthorn—could be harnessed to control the shrub, allowing native plants to replace it.

"We have identified four species in Minnesota that will be greenhouse- and field-tested against buckthorn this summer,” he says.

Thanks to all these and other researchers, Minnesota is starting to turn the tide against this pesky plant.

Volunteers in the spotlight

Stephanie Snell, Minnetonka

“My husband and I volunteered an area of our backyard forest as part of [a Cover It Up] study,” says Snell. “We got to observe when the native seeds started to sprout and all kinds of new native plants started to grow! I was thrilled to be able to participate in a project that would help with research the Department of Forest Resources was doing, while also helping the native species in our yard.” 

Ralph Hanson, Glenwood

“We have a serious buckthorn infestation in our woods, and I’m interested in all the information I can get on how to fight it,” says Hanson. “The study work consisted of clearing existing buckthorn from six small plots, planting half with buckthorn seeds alone and the other half with buckthorn seeds and a native plant seed mix, then gathering data on the resulting growth. Aside from clearing a buckthorn thicket and seeing the possibility of its reclamation by native species, my enjoyment has come from being part of a citizen science project and contributing to useful research.”

Supportive partners

The Minnesota Invasive Terrestrial Plants and Pests Center is funded largely by the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources.

Give to the Minnesota Invasive Terrestrial Plants and Pests Center