The purple spotted knapweed flower is attractive to bees and a good nectar producer: However, once it gains a foothold, spotted knapweed kills competing vegetation and creates conditions for its own spread.
Photo by James H. Miller, USDA Forest Service, Bugwood.org photo Inset by Marisa Williams, University of Arkansas, Bugwood.org
Michigan beekeepers have added one more item to the list of things threatening their industry—a gradual reduction in a major bee forage crop they call star thistle.
In August, the state Department of Agriculture approved the release of two biocontrol agents—beetles—that feed on spotted knapweed, an exotic, invasive weed species that has spread over much of North America since it was brought here from Europe and Asia about 120 years ago.
Spotted knapweed which many beekeepers call by the more romantic name of star thistle, has spread over much of northern Michigan in the last 50 years. In July and August, the sandy northland, much of it state-owned and not adaptable to farmland, turns purple, and over the years, many beekeepers have established bee yards to collect the nectar.
Star thistle honey from Michigan is a name brand, like tupelo honey from the South.
Michigan beekeepers use their bees to pollinate the state’s fruit and vegetable crops each spring and then move to star thistle and its large nectar flows in late summer. The state ranks in the top ten in colony numbers, with about 72,000 of the nation’s 2.3 million colonies.
Terry Klein, a beekeeper with 1,000 colonies in eastern Michigan near Saginaw, has been vocal in opposition to the release of the biocontrol agents. He says the Michigan bee industry is highly dependent on star thistle, and that without it the industry might not be able to sustain itself and provide the pollination services Michigan fruit and vegetable growers need. About 42 percent of the crop income of Michigan farmers comes from specialty crops, and supplemental bees are needed in cucumbers, sweet and tart cherries, apples, blueberries, and other crops.
Ken Rauscher, head of the Michigan Department of Agriculture’s Pesticide and Plant Pest Management Division, said the department has been keenly aware of the beekeepers’ reliance on star thistle. In the past, the department has not supported biocontrol plans—even as other states were adopting them—because of the beekeepers’ concerns. But land managers in other units of state and local government—those who manage state forests and parks and other property—have increasingly wanted to strike back at star thistle, which has been displacing native plant species for many years and converting their “natural” areas into weed-infested wastelands.
Spotted knapweed is an aggressive plant, Rauscher said. It gets a start in disturbed soil, along roadsides and in old fields that are no longer tilled (of which northern Michigan has many). Once started, it releases a chemical that keeps other plants out and creates conditions for more knapweed. It just keeps moving into new territory.
The Michigan Department of Agriculture became convinced last summer that both beekeepers and those who want to control spotted knapweed could be winners, Rauscher said. Michigan State University entomologist Doug Landis, who has managed a successful biocontrol program against the exotic marshland invader purple loosestrife, proposed a pilot program in which star thistle would be attacked in selected sites. As a vital part of the plan, native species of wildflowers that bloom in the star thistle period would be planted in the release sites. The idea is that as star thistle retreats, these wildflowers will advance, and there’ll be no net loss of forage for Michigan beekeepers.
It won’t take place overnight, Landis said, nor will it result in complete elimination of spotted knapweed. “It will begin to show impacts after three to five years as the biocontrol beetles become established, and there will be a slow decline of knapweed. Eradication or elimination is not possible or a goal of this program,” he said.
The six sites where the releases were made last August are on public lands, and the land managers involved are now evaluating a list of 17 native plant species that bloom at the same time as knapweed to decide which ones will be frost-seeded this spring.
Landis noted that beekeepers themselves are not comfortable relying on a monoculture of star thistle. In some years, it has a crop failure with a resulting large impact on honey production. “Beekeepers are very reliant on a single plant species,” Landis said of star thistle. “We think replacing it with a diversity of plants will add reliability to the nectar flow and be a win-win for everybody.”
One beekeeper who endorsed the plan is Roger Hoopingarner, a retired Michigan State University entomologist who led the entomology department’s bee program for many years and is now president of the Michigan Beekeepers Association.
There’s been a big exchange of letters on the beekeepers’ Web site between Hoopingarner and beekeepers who think he didn’t defend their interests. Hoopingarner and Landis agree that biocontrol is a good idea, that the phase-in program is a good plan, and that biocontrol was coming whether or not Michigan wanted it.
The biocontrol beetles have been released in several other nearby states, including Minnesota and Wisconsin, where they have become established and are moving to other spotted knapweed-infested areas. In fact, Landis said, several less-highly-publicized releases had also been made in Michigan. In the West, spotted knapweed is a major problem on cattle pastureland. Cattle don’t like it, it is somewhat toxic if they eat it, and it crowds out native grasses. The West has adopted the biocontrol option wholeheartedly.
Beekeeper Klein questions how it will work. If the beetles kill the knapweed, but the knapweed chemicals persist in the soil, the plan might produce bare ground rather than new native species. Landis sees the process as taking a longer time frame. Part of his research will look at how well plants move back into areas as knapweed is removed.
Klein says the beekeepers have enough problems, with predator mites and Colony Collapse Disorder. But Landis sees the biocontrol program not as another epidemic, but a gradual program in which spotted knapweed gets rolled back and new, nicer flowering plants return to the landscape from which knapweed drove them.
The pilot program will be evaluated, and Michigan officials don’t expect to release more biocontrol insects until they see favorable results. Landis noted that several federal and state programs are now available to help landowners pay the cost of planting native wildflowers on private land. If the beetles are successful, they won’t stay on publicly owned land.