People fight buckthorn with everything. They cut them with chain saws, yank out the seedlings, douse stumps with Roundup, imprison them under coffee cans and shovel out the roots. They sic goats on them.

But buckthorn springs back to life like a zombie, a pernicious invasive, with multiple strategies to outcompete native plants and take over a 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 famously tough-to-kill plant.

Researchers tried for years to find an insect to do the job, with no success. Meanwhile, the invasion of buckthorn and its removal is estimated to have cost Minnesota millions, not including all the hard-to-quantify impacts from lost native biodiversity, said Mike Schuster, an invasive plant specialist in the university's Department of Forest Resources.

The new potential ally is crown rust, or Puccinia coronata, a fungus found on most buckthorn plants in the state. Crown rust is a notorious attacker of wheat, oats and barley that's been studied for more than 100 years, but never for the potential to control its buckthorn host, said Pablo Olivera Firpo, the U plant pathologist leading the project.

Crown rust starts out looking like orange measles on buckthorn then grows into raised cluster cups, a mass of little spore-spreading tubes. Some of the masses resemble a fuzzy caterpillar crawling up a stem.

"Can the rust suppress the growth of seedlings ... or kill them?" That's the question that preoccupies Olivera Firpo.

Trouble is, nobody knows how many of the 17 known crown rust species in the world exist in Minnesota, or which ones are most destructive to buckthorn. Olivera Firpo's team plans to figure that out with a three-year $364,000 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, researchers plan to attack the buckthorn using a mat of straw infected with the fungus. After buckthorn trees and shrubs have been hacked down, the mat would be spread over the area to stop the prolific seedlings from re-sprouting.

"In an ideal world, that's the product," said Nick Greatens, a post-doctoral researcher on the project.

For now, Greatens and the team are collecting hundreds of samples of crown rust-infected buckthorn plants. Common buckthorn, the most prevalent in Minnesota, and glossy buckthorn are the two species brought to Minnesota in the 1800s as ornamental shrubs and privacy hedges. The state restricts them as noxious weeds.

A laboratory on the U's St. Paul campus holds a collection of rust-infected 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.

Researchers vacuum up spores, freeze the samples, extract the DNA and sequence it to identify the species. Then they will inoculate buckthorn seedlings to find the types that best suppress seedling growth.

Olivera Firpo's team is not the only one probing fungi as a buckthorn biocontrol. Across the hall, a separate team with another Minnesota Invasive Terrestrial Plants and Pests Center grant takes a broader approach. They are sleuthing out dying buckthorn plants around the state and studying the organisms killing them to see if they could be exploited for biocontrol. They're not targeting crown rust, but different fungi that cause cankers on the plant and also wilt pathogens, said Robert Blanchette, the plant pathologist leading that project.

The answers can't come fast enough.

Everything about buckthorn seems designed to make it thrive. The berries on female plants contain a laxative ensuring birds spread it widely, and the roots emit a chemical in the soil that inhibits other plants.

Alexandra "Sascha" Lodge, terrestrial invasive species coordinator at the Department of Natural Resources Forestry Division, would welcome an assist from a native fungi. Because buckthorn is shade tolerant, it proliferates in forests where it quickly crowds out other plants and wildlife. The department treats state forest lands for buckthorn the year before a timber harvest.

Buckthorn is a nightmare to remove, said James Shaffer, natural resources supervisor for the Minneapolis Parks and Recreation Board. He'd love a non-herbicide option: "I've been hoping to see something like this pop up."