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Dec 31, 2012
Loss of ‘invasive’ plant could hurt pollination in Michigan

Michigan beekeepers are worried about a project that could shrink the number of spotted knapweed plants (also known as star thistle) in the state. If the star thistle population is reduced, or possibly eliminated, it could wipe out a prime source of honey for the state’s beekeepers – which could lead to higher pollination costs for the state’s fruit and vegetable growers, said Tim Dekorne, president of the Michigan Commercial Beekeepers Association.

The project, managed by the Michigan Department of Natural Resources (DNR) and Michigan State University (MSU), is attempting to reduce the spotted knapweed population because it’s “one of the most serious invasive plants in North America,” according to an MSU fact sheet.

The problem is that star thistle might be the most important source of nectar in the state today, producing millions of dollars’ worth of honey, according to Roger Hoopingarner, past president of the Michigan Beekeepers’ Association.

Dave Smith, executive secretary of the Michigan Vegetable Council, said the elimination of the star thistle could threaten the viability of commercial beekeepers in the state, who play an important role in the production of vegetable and fruit crops. With fewer beekeepers, growers would have to spend more for pollination services.

“Some of them spend a fair amount of money as it is,” Smith said.

There are 40 or 50 commercial beekeepers in Michigan, who supply 90 percent of the state’s honeybee hives, said Dekorne, a commercial beekeeper himself. Right now, those beekeepers charge growers an average of $50 to $60 per hive. If the beekeepers lose access to prized star thistle honey, however, those pollination prices could conceivably rise to California levels, perhaps $145 to $165 per hive, he said.

“Beekeepers are essential to the pollination process for our apple growers,” said Diane Smith, executive director of the Michigan Apple Committee. “We understand the current challenges beekeepers are facing and we sympathize with their situation. Our board will remain in contact with the beekeepers in an effort to support sustainability of the apple industry in Michigan.”

According to the MSU fact sheet, spotted knapweed – an exotic plant that originated in Europe and Asia – was first found in Michigan in 1911. The non-native plant can eventually “reduce the diversity of native plants in infested areas, which in turn can reduce the diversity of insects, birds and other wildlife. On highly disturbed soils like roadsides and former agricultural fields, spotted knapweed can form nearly solid, single-species stands that provide a foothold in the landscape from which it can spread into nearby areas.”

In Michigan, spotted knapweed is a particular threat along the Great Lakes, where it artificially stabilizes coastal dunes and can result in a loss of biodiversity, according to MSU.

To suppress the invasive plant in Michigan, federal and state government projects have released biological control agents – flies and weevils – within the last two decades. In the summer of 2010, MSU – in cooperation with and with funding from the state DNR – released a root-feeding weevil and two species of flower weevils on six public sites. The weevils were chosen because they’ve successfully suppressed spotted knapweed in other states, according to MSU.

The biological control efforts could reduce the density of spotted knapweed by more than 80 percent, according to MSU.

Eighty percent is a “big chunk of change,” Dekorne said.

“That’s 80 percent of our income, in some cases.”

Dekorne said the weevils will spread, and could wipe out the state’s entire star thistle population.

According to the MSU fact sheet, however, biological control efforts “cannot eradicate or eliminate a weed. Thus, spotted knapweed will likely always be a part of Michigan’s flora.”

To replace the lost nectar from lost spotted knapweed plants, the six release sites were seeded with nectar-producing native plants, according to MSU.

“The expectation is that as knapweed declines, the native plants will fill the vacant niches and produce a comparable nectar flow,” according to the fact sheet.

It will take time to see if the native plants produce nectar as well as the star thistle does, according to Hoopingarner.

At any rate, it’s too late to reverse course – but commercial beekeepers want to be kept informed of any future releases of biological control agents, Dekorne said.

“We’ve been pushing no more releases on the thistle, or any other plants, unless we know about it first,” he said.

MSU is still studying the prior biological control releases, and doesn’t have plans for additional releases at this time, said Doug Landis, an MSU entomology professor and the project’s lead investigator.

By Matt Milkovich, Managing Editor





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