People fight buckthorn with everything. They cut them down with chain saws, pull out the saplings, douse the stumps with Roundup, imprison them under coffee cans and rake up the roots. So do goats on them.
But buckthorn comes back to life as a zombie, an insidious invader, with multiple strategies to overrun the native flora and take over the landscape.
Now University of Minnesota scientists are studying whether they can turn the plant on itself, exploiting an orange fungus that buckthorn hosts. If they succeed, the result could be the first environmentally friendly natural biocontrol, other than hungry goats, for a notoriously hard-to-kill plant.
Researchers have tried for years to find an insect to do the job, to no avail. Meanwhile, the infestation and removal of buckthorn, estimated to cost Minnesota millions, does not include all the hard-to-quantify traces of lost local biodiversity, said Mike Schuster, an invasive plant specialist in the university’s Department of Forest Resources.
A new potential ally is crown rust, or Puccinia coronata, which is a fungus It is found in most buckthorn plants in the state. Crown rust is a notorious attacker of wheat, oats and barley and has been studied for more than 100 years, but never for its ability to control its buckthorn host, said Pablo Oliveira Firpo, a U plant pathologist who leads the project.
Crown rust begins to look like orange measles on buckthorn and then grows into raised racemose cups, a mass of tiny spore-spreading tubes. Some masses resemble a fuzzy caterpillar crawling up a leg.
“Can rust prevent seedlings from growing…or kill them?” This is the question that preoccupies Oliveira Firpo.
The problem is that no one knows how many of the world’s 17 known crown rust species are found in Minnesota, or the most destructive species of buckthorn. Olivera Firpo’s team plans to find out with a $364,000, three-year grant from the Minnesota Invasive Terrestrial Plants and Pests Center, supported by the lottery-funded Environment and Natural Resources Trust Fund.
If they find a suitable strain that doesn’t affect crops, the researchers plan to attack the buckthorn with a straw mat infected with the fungus. After the buckthorn trees and shrubs are cut down, a mat will be spread over the area to prevent the abundant seedlings from re-germinating.
“In an ideal world, that would be the product,” said Nick Greitens, a postdoctoral researcher on the project.
At the moment, Greitens and the team are collecting hundreds of samples of buckthorn plants infected with crown rust. Common buckthorn, which is most widespread in Minnesota, and glossy buckthorn are the two species that were brought to Minnesota in the 19th century as ornamental shrubs and privacy hedges. The state restricts them as weeds.
One of the labs on the U’s St. Paul on a collection of rusted buckthorn leaves and twigs from William O’Brien State Park, Brown’s Creek State Trail in Stillwater and Reservoir Woods Park in Roseville, among other places.
The researchers vacuum out the spores, freeze the samples, and extract and sequence the DNA to identify the species. Then they pollinate the buckthorn seedlings to find the ones that best inhibit the growth of the seedlings.
Oliveira Firpo’s team isn’t the only one probing the fungus as a buckthorn biocontrol. Across the hall, a separate team with another grant from the Minnesota Center for Invasive Terrestrial Plants and Pests is taking a broader approach. They are searching for dying buckthorn plants across the state and studying the organisms that kill them to see if they can be exploited in biological control. They’re not targeting crown rust, but various fungi that cause cankers on the plant and also wilt pathogens, said Robert Blanchett, the plant pathologist leading the project.
The answers can’t come fast enough.
Everything about buckthorn seems designed to make it thrive. The berries on the female plants contain a laxative that ensures they spread widely, and the roots emit a chemical into the soil that inhibits other plants.
Alexandra “Sasha” Lodge, terrestrial invasive species coordinator in the Department of Natural Resources’ Division of Forestry, would welcome help from native fungi. Because buckthorn is shade tolerant, it thrives in forests where it quickly crowds out other plants and wildlife. The department treats state forest lands for Nabq in the year prior to the timber harvest.
Buckthorn is a nightmare that needs to be removed, said James Shaffer, superintendent of natural resources for the Minneapolis Parks and Recreation Board. He liked a non-herbicide option: “I was hoping to see something like that pop up.”
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