People fight buckthorn with everything. They cut it down with a chain saw, pulled out the saplings, doused the stump with Roundup, imprisoned it under a coffee can and uprooted it. So did the goats on them.
But buckthorn comes back to life as a zombie, a dangerous invader, with various strategies to invade native flora and take over the landscape.
Now University of Minnesota scientists are studying whether they can revive the plant itself, exploiting the citrus fungus that hosts the buckthorn. If successful, the result could be the first environmentally friendly natural biocontrol, other than hungry goats, for a plant that is notoriously hard to kill.
Researchers have tried for years to find insects to do the job, without success. Meanwhile, the infestation and cull of buckthorn, which is estimated to cost Minnesota millions of dollars, excludes all the hard-to-quantify traces of local biodiversity loss, 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 of the buckthorn plants in the state. Crown rust is a well-known invader of wheat, oats and barley and has been studied for more than 100 years, but never for its ability to control buckthorn hosts, said Pablo Oliveira Firpo, the U plant pathologist who led the project.
Crown rust starts out looking like orange measles on buckthorn and then grows into raised racemose cups, masses of tiny tubes that disperse spores. Some of the masses resemble downy caterpillars crawling on the legs.
“Can rust prevent seeds 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 damaging species of buckthorn. Olivera Firpo’s team plans to find out with a three-year, $364,000 grant from the Minnesota Invasive Terrestrial Plants and Pests Center, supported by a lottery-funded Natural Resources and Environmental Trust Fund.
If they find a suitable strain that doesn’t affect the crop, the researchers plan to attack the buckthorn with straw bedding infected with the fungus. After the trees and buckthorn bushes have been cut down, mats are spread over the area to prevent the bountiful seedlings from germinating again.
“In an ideal world, that would be the product,” said Nick Greitens, a postdoctoral researcher on the project.
Currently, Greitens and his team are collecting hundreds of samples of buckthorn plants infected with crown rust. The common buckthorn, the most widespread in Minnesota, and the glossy buckthorn are two species brought to Minnesota in the 19th century as ornamental shrubs and privacy hedges. The state restricted them as weeds.
One of the laboratories at U’s St. Paul on a collection of rusty 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 aspirated the spores, froze the samples, and extracted and sequenced the DNA to identify the species. Then they pollinated the buckthorn seedlings to find the ones that best inhibited the growth of the seedlings.
Oliveira Firpo’s team is not the only one investigating mushrooms as 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 searched the state for dying buckthorn plants and studied the organisms that killed them to see if they could be exploited in biological control. They don’t target crown rust, but a variety of fungi that cause cankers in plants as well as wilt pathogens, said Robert Blanchett, the plant pathologist who led the project.
The answers can’t come fast enough.
Everything about the buckthorn seems designed to make it thrive. The berries on the female plants contain a laxative that makes them spread widely, and the roots secrete chemicals into the soil that inhibit other plants.
Alexandra “Sasha” Lodge, coordinator of terrestrial invasive species in the Forestry Division of the Department of Natural Resources, will receive assistance from native mushrooms. Because the buckthorn is shade tolerant, it thrives in forests where it quickly crowds out other plants and wildlife. The department treats state forest land for Nabq in the year before logging.
Buckthorn is a nightmare that needs to be dispelled, says James Shaffer, natural resources supervisor for the Minneapolis Parks and Recreation Council. He likes non-herbicidal options: “I was hoping to see something like that come out.”
2023-06-28 14:36:55
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