http://ipraudio.interlochen.org/Knapweed_Thistle.mp3
Last summer, researchers from Michigan State University released two foreign beetles on state forest land. The experiment is to see if the bugs will control an invasive plant called spotted knapweed that spreads wildly over old farm fields and alongside roads.
Knapweed crowds out native plants that support insects, birds and other wildlife. But there is one insect that likes spotted knapweed, honey bees. And their owners don't want to see the plant go away.
Biological Control
It's the use of insects to control non-native plants. Researchers say bio-control is working pretty well against spotted knapweed in several states. In Minnesota two kinds of weevils released together have knocked knapweed back as much as 80 percent on test plots. One weevil feeds on knapweed's roots while the other eats its seeds.
"These insects don't eliminate knapweed," explains Doug Landis, a bug specialist at Michigan State University. "None of the bio controls can actually eliminate or eradicate this plant. But they can reduce its density to the point where it becomes a more manageable part of the plant community."
Knapweed is widespread in northern Michigan. It tends to be the dominant plant especially on poor sandy soils that have been disturbed, like abandoned farm fields. And knapweed is tough to get rid of because it secretes a chemical substance that kills nearby plants. Its seeds also live in the soil for a long time.
Weed... or Thistle?
But beekeepers say it has a lot of value for them. They even have a more poetic name for it, star thistle. And they say it produces a brand of honey that puts northern Michigan on the map.
"It's one of the best honeys in the country," says Kirk Jones, who runs Sleeping Bear Apiary in Benzie County. His star thistle honey ends up on store shelves and in restaurants across the country.
Jones depends on that carpet of purple flowers that blooms across fallow fields in mid-summer. He says it's the only source of surplus nectar around here that keeps his bees making barrels of honey late in the season.
"And without that source of nectar to make honey we wouldn't be able to keep bees here," he says. "And then there would be a spin-off of not having a robust bee population for everybody to pollinate their flowers to make food."
Good Alternatives?
But researchers don't plan to take away star thistle and leave bee keepers high and dry. Their plan is to replace it with a mix of native wildflowers, and they say they've already found a couple of dozen species that will be good substitutes.
Doug Landis thinks it won't hurt the bee business if some fraction of knapweed is replaced.
"If we are able to, over the next decade or longer, reduce the amount of knapweed or replace it with a native nectar source, I believe consumers would be very happy to buy a native Michigan wildflower honey whether it says star thistle on it or not," he says.
Star thistle has been established in this country for more than a hundred years. Bee keeper Kirk Jones sees it as part of an ongoing progression of plants that adapt and replace what was previously here, and he doubts that wildflowers will ever match its nectar flow.
"There may be good intentions," he says. "But I think it's probably of dubious value to try to return old farmland to some point in time in the past."
But public land managers say it's worthwhile to try to keep spotted knapweed in check at least in a few places. They're working to re-establish native plants and grasses that host a lot more insect food and cover for a much larger variety of wildlife than a field full of star thistle ever will.
The six test plots, each much smaller than an acre, are dotted along a line that runs up the center of the state from southern Michigan to the Upper Peninsula.