The Michigan Department of Agriculture and Rural Development is looking for public feedback to determine whether it should issue permits that would authorize the release of two species of beetles. The beetles are meant to help control invasive spotted knapweed across the state.
Spotted knapweed is a perennial plant with thistle-like pinkish-purple flowers. Mike Philip, the director of MDARD’s Bureau of Environment and Sustainability, said the plant isn’t native to North America, but has gained a strong foothold in the United States. Knapweed was first found in Michigan in 1911, he said. Now, it’s widespread throughout the state.
“Typically, you will run into spotted knapweed in disturbed sites, for example, roadsides or abandoned fields, things like that,” Philip said. “But it is also found very, very commonly in some sensitive habitats, like dunes and lakeshores.”
Philip said the spotted knapweed can outcompete native plants by producing thousands of seeds and chemicals that inhibit other plants in the vicinity from growing.
“So for those reasons, it outcompetes and its populations can really grow, and then that impacts the native ecosystem,” Philip said.
The biggest concern is the knapweed’s ability to displace native plants, which can result in cascading consequences on ecosystems, especially sensitive ecosystems, Philip said.
But the plant has some benefits. Philip said spotted knapweed blooms in late summer, when few other plants are blooming, and provides a key late-season nectar source for beekeepers.
“The honey that it produces is of very high quality, and so they value it quite a bit,” Philip said. “Native pollinators, like butterflies and bees, they will also nectar at knapweed, and native pollinators are in decline, and so that's just something to be cognizant of.”
The state agriculture department is in the midst of a process to decide whether Michigan will issue permits for releasing seedhead and boring weevils to control the growth of the knapweed. The federal government used to be in charge of the authorization process, but after determining the weevils posed little risk risk, the decision now rests with states.
“I think our number one goal is simply to make the best decision, one that reflects where science is and one that reflects what the public's interest in this is,” Philip said.
Seedhead weevil feeds on the developing seeds of the knapweed, reducing the reproduction of the plant, and root boring weevils feed on the roots of the plant, reducing its health.
“Taken together, they have the potential to reduce knapweed populations,” Philip said. “They do not eliminate the plant, that is not how beneficial insects like this work. But they can mitigate the impact of an infestation of knapweed.”
Philip said the weevils pose a small environmental risk because they feed only on knapweed. “If you were to take away knapweed and give them all different other plants and tell them, 'eat one of these other plants or die,' they will die,” he said.
The public can provide feedback on the proposal by filling out an online survey, which is open until March 6.
