Invasives threaten local environment


An Invasive Species Network (ISN) volunteer holds an armful of garlic mustard removed from Clay Cliffs Natural Area. Photos courtesy of ISN

By Ross Boissoneau

Sun contributor

They may be beautiful. They may look nice as lawn ornamentation. They may even be as familiar as the bouquet from the florist. But make no mistake: non-native plants and animals threaten native flora and fauna as well as the enjoyment residents and visitors derive from the area.

Knotweed, barberry, baby’s breath and Eurasian milfoil are just a few of the invasive species found in our fields and forests, lakes and waterways. Some target specific hosts, such as hemlock wooly adelgid, and before that, the emerald ash borer. Others simply crowd out native plants, such as garlic mustard or autumn olive.

The Northwest Michigan Invasive Species Network works with a number of partners, including the Leelanau Conservancy, the Michigan Department of Natural Resources, the Leelanau Conservation District, the Grand Traverse Band of Ottawa and Chippewa Indians, Sleeping Bear Dunes National Lakeshore and numerous private landowners to combat these and other invasives. “We try to be a source of knowledge: what plants are invasive, restoration practices, etc.,” says Audrey Menninga, Invasive Species Network Coordinator.

As you might expect from its name, the folks at the Invasive Species Network are on the front lines, both educating the public and working in the field alongside the organization’s many partners. Currently, there are crews working on treating hemlock wooly adelgid and garlic mustard.

The former is an aphid-like insect that attacks the base of hemlock needles, stealing its nutrients and starving the tree. It can kill hemlock trees in as little as four years. In the fall and winter, the adelgids cover themselves with a white, waxy coating for protection that appears as woolly bundles the size of a pinhead – hence the name.

“Hemlock wooly adelgid doesn’t winter well,” says Menninga. That’s why it isn’t found — yet – in the middle of the state, but instead in coastal areas nearer the warming effect of Lake Michigan. That also means the mild weather of this past winter could hasten its spread.

Sleeping Bear Dunes National Lakeshore announced earlier this year it was closing the Old Indian Trail and surrounding area due to an infestation of hemlock wooly adelgid (HWA). Surveys in January and February found a large infestation on the southern boundary of the National Lakeshore, along and around the area of the Old Indian Trail. The hope is that after treatment the trail will be reopened by the fall of 2024.

“If they’re treated, we see good results,” Menninga says. “Chemicals will give five to seven years of protection, as long as the trees are not too stressed.” Still, she says it’s unlikely the pest will ever be completely eliminated. “The focus is to slow the spread.”

While HWA has always been seen as an invasive threat, garlic mustard was once seen as beneficial. Perhaps the headline at the Nature Conservancy says it best: “Garlic Mustard: Invasive, Destructive, Edible.” It was introduced to North America in the 1800s for its herbal and medicinal qualities and as erosion control.

But it spread far more quickly than native plants could keep up, and it quickly crowds out other plants. Because the forest floor is so important for insects and other species at the bottom of the food chain, garlic mustard can weaken the entire ecosystem.

“Garlic mustard is having a great season,” Menninga says wryly. “It’s flourishing everywhere.” Again, she lays part of the blame on the mild winter.

The plant can be used as salad greens, though she says its bitter taste limits the amount most people would care for. It can also be used in pesto, and Menninga says that Oryana even used it in minestrone soup.

However, harvesting the plant for use will never be enough to control it, so removing it by pulling or using herbicides are the best ways to eliminate it. There are dumpsters at the Clay Cliffs Natural Area and in Empire to dispose of plants pulled. She says it is important to stop removing the plant when the seed pods mature, as the motion triggers the pods to explode, scattering seeds everywhere.

Menninga says crews now treating hemlock wooly adelgid and garlic mustard will subsequently move on to attack knotweed and baby’s breath. The organization works with numerous private landowners on the former, while the latter is a problem for the dunes. “Our sand dunes are shifting dunes,” says Menninga, which a number of native plants rely on to scrape the seed coatings and expose the seeds.

Baby’s breath prevents that action. “Baby’s breath has a tap root that’s ten feet deep,” she says, anchoring the plant and the dunes. Worse yet, come fall the plant breaks away from the root and acts like a tumbleweed, crossing the dunes and dropping its seeds as it spreads, and again crowding out other plants. Menninga says one example is Pitcher’s thistle, which while it seems plentiful, is federally listed as a threatened species. Baby’s breath is one of its biggest threats as it will outcompete Pitcher’s thistle.

For more information on any of these threats to the area and how to combat them, visit In a future edition of the Glen Arbor Sun, we’ll take a look at some of the aquatic invasives and what’s being done to combat them.