March 3, 2024

Up North's Least Wanted Invasive Species

The dirty dozen
By Ross Boissoneau | July 31, 2021

You won’t see them on posters at the post office. But make no mistake, these threats to our fields and forests, lakes and streams are most unwelcome. A huge number of plants, animals, and insects are recognized as non-native threats to the state. Many of them are even prohibited to own in Michigan.

Numerous organizations and governmental agencies are working to identify, control, and/or eradicate these pests while scientists, field workers, and ordinary citizens are using various means — natural, chemical, and mechanical —  to address the situation, whether the offender is homegrown or not. “[It’s] those that do damage, not just non-native. Those that harm human health, the environment, or our ecology,” says Eli Baker, education and outreach specialist at Tip of the Mitt Watershed Council.

The following is not meant to be a comprehensive list, as there are many others that could be included (for a complete list, go to Think of it as the highlights — or maybe the lowlights — of the things we wish weren’t here.

Invasive Phragmites

Introduced via ship ballast in the late 1700s or early 1800s, the plant is now illegal to sell, trade, plant, or share in Michigan. Invasive phragmites can clog wetlands, as their stems and rhizomes catch sediments, eventually filling in small waterways.  Its height and thickness can prevent waterfowl from using invaded areas as a home or even a stopping point. With the potential to grow over six feet high, phragmites can make it near impossible for many native species to access wetlands and commonly impede the views from waterside properties.

Purple loosestrife

Think of it as the near-perfect invader: Introduced from Eurasia via ship ballast and intentionally planted as an ornamental garden flower in the 1800s(!), the undeniably pretty but deadly purple loosestrife bears seeds that germinate very rapidly and grows faster than almost any other wetland plant.  The problem? This cruel beauty — now illegal to sell, trade, plant, or share in Michigan — not only reduces critical food resources for birds, butterflies, and other wild creatures but also boasts stiff stems that collect so much debris, they can entirely dry up shallow waters, destroying the habitat for native aquatic animals that have been living there.  

New Zealand mud snail

Joanne Foreman, invasive species communication coordinator for the state’s Department of Natural Resources, Environment, Great Lakes and Energy, and Department of Agriculture and Rural Development, says the New Zealand mud snail is one of the greatest aquatic threats out there: it’s very small, reproduces quickly, and can survive in or out of the water. They eat a lot of the lowest levels on the food chain, but when ingested by fish on the next level, the snails offer no nutritional value and simply pass through the fish. Unfortunately, these snails prefer the same habitat as trout — bad news for anglers looking to catch big, healthy fish. They are currently in the Au Sable, Pere Marquette, Boardman, and Manistee Rivers. Even worse, because New Zealand mud snails can survive out of the water, they can be easily transferred on waders, meaning no trout stream is safe. “There’s no magic bullet,” Foreman says. But anglers can help stem the by thoroughly cleaning off their waders before moving from one river to another.

Zebra mussels

Some four decades after they first gained a foothold in the Great Lakes, zebra mussels are still causing economic and human health concerns, says Baker. They’ve also moved inland, likely transported by boaters who moved their watercraft from one waterway to another without cleaning off their boat. Lakeshore residents around northern Michigan have reported entire colonies attached to their docks, boat hulls, and water intake pipes. Prolific reproducers, each zebra mussel can filter a liter of water per day, removing almost every microscopic aquatic plant and animal. Not only does this disrupt the food chain, but the resulting clearer water also permits sunlight to penetrate deeper into lakes, resulting in increased growth of rooted aquatic vegetation and bottom-dwelling algae. That said, they are a lower priority than the next member of the Dirty Dozen.

Quagga mussels

Even though Quagga mussels are less common than zebra mussels, Baker says quaggas pose a greater threat; they have a wider distribution and can survive both deeper waters and colder temperatures. Jane Perrino, Aquatic Invasive Species Coordinator for the Benzie Conservation District, says their ability to adapt makes them particularly formidable. “They can reposition themselves if disturbed, and they don’t need a hard substrate,” she says. “They can settle in on all kinds of surfaces” — sandy lake bottoms included.

Good Harbor Reef is a good example. There, quagga mussels have blocked spawning sites for whitefish, lake herring, lake trout, and other native aquatic species. The negative impacts extend to the Sleeping Bear Dunes National Lakeshore, where dead algae and mussel shells are creating a nuisance and a hazard for park visitors when they wash up on beaches. In addition, the area has experienced problems with the botulism toxin — likely driven by the dead algae invasive mussels have introduced into the food — leading to the death of fish and water birds. 

One of the biggest challenges for both species of mussels and the many other invasives is the cost of addressing them. “What the party [trying to address the problem] is pursuing and how deep their pockets are” are huge factors in the efforts to eradicate mussels, Perino says.

Eurasian Water Milfoil

Milfoil has invaded countless waterways around the region. Biologist Brian Price, formerly executive director of the Leelanau Conservancy, calls Eurasian watermilfoil one of the worst invaders. “It packs a big punch — it can plug navigation, impact recreational values and property values.”

Tom Hiatt, president of the Lake Leelanau Lake Association, knows the issue well. LLLA is undertaking a major effort to eradicate its Eurasian Water Milfoil problem with benthic barriers — large 400-by-40-foot sheets of plastic or burlap spread on the lake bottom to prevent photosynthesis — and plenty of manpower: Divers pull by hand any milfoil that escapes the barrier, then carefully raise it to the surface in bags or vacuum tubes. Any pieces that escape can reroot. Hiatt says a cooperative effort with the association and the Grand Traverse Band resulted in a three-year grant and plan. A recent $5 million gift from a donor with longtime intergenerational ties to the lake will be dedicated to controlling the spread of milfoil and other aquatic invasives.

Rick Kiehle is Hiatt’s counterpart at Long Lake in Grand Traverse County. He says the association there has used drones to identify infestation areas. “Our lake is deeper, and we only get it in certain areas,” he says. Kiehle says the biggest challenge is to prevent further infestations from milfoil or any other invasive species, and the key is to persuade people to wash their boats and trailers whenever they move them from one body of water to another.

Japanese and common barberry

A spiny shrub whose arching branches are characterized by green or blue-green, oval or spoon-shaped leaves, both barberry species have been used as a common horticultural plant. However, it has frequently escaped from yards and has been found in the wild in Benzie, Grand Traverse, Leelanau, and Manistee counties. Left to grow, it forms dense thickets that reduce habitat for birds, butterflies, and other animals. The dense foliage also increases humidity levels within the canopy, leading to higher tick populations. Unwanted occurrences in natural areas can be controlled using both mechanical and chemical techniques. Due to their shallow root systems, Japanese barberry can easily be pulled or dug up.  

Garlic mustard

Introduced as food and medicine to North America from European settlers in 1868, garlic mustard crowds out native plants, especially spring ephemerals like trillium and violets. It also releases chemicals into the soil that hinder the growth of other plants. Furthermore, few native herbivores will eat garlic mustard, giving it even more competitive advantage over native plants. Worst of all, garlic mustard seeds are able to live in the soil for at least seven years before sprouting.

Garlic mustard is an extremely hardy plant, and can re-sprout in a compost pile or if left out, and seeds can develop even if the plant was not flowering when pulled.  Pulling garlic mustard is very effective in small populations. Price compares it to Eurasian water milfoil, saying both are hardy and spread easily. “You need to battle them both all the time.” 


Another plant introduced as an ornamental, knotweed, like other invasives, crowds out native plants while providing little in the way of food or habitat for native wildlife. Knotweeds are problematic for infrastructure as well, as the plant can sprout up through concrete and asphalt, spread quickly, and is difficult to eradicate. Knotweeds are very hardy and can tolerate ash, sulfur, and toxic gases, as well as high salinity, full shade, high temperatures, and drought. For all these reasons, Japanese knotweed and its hybrids/cultivars are prohibited in Michigan.  

Beech bark disease

Kama Ross, regional forester with the Grand Traverse Conservation District, says this is one of the most important threats facing the region. “My big concern is beech bark disease. It’s catastrophic. It will kill 98 percent of beech, and the northern hardwood [forest] is predominantly beech and maple. It will be a huge change for the forest system,” she says. The disease is a fungus introduced through extensive bark invasion by the beech scale insect. It produces cankers, areas of dead tissue, which will eventually girdle the tree and kill it. First detected in Ludington State Park in the ’80s, beech bark disease has migrated throughout the state. It is spread through a variety of means: wind, birds, insects, and people.

Hemlock wooly adelgid

This insect — like many other invasives, a native of Asia — feeds by sucking sap from the base of the host tree's needles. This disrupts the flow of nutrients, slows growth, and causes the tree's dark green needles to discolor and turn grayish-green, eventually falling off. Foreman says the state’s 190 million hemlocks are all in danger — and that puts a lot of other species in danger too. “Hemlocks are a major part of the northern forest,” Foreman says. “They shade waterways, help wildlife and fish.”

Previously thought to be a problem south of this region, Hemlock wooly adelgid has arrived in northern Michigan. “There’s one site in Leelanau County and one in Benzie,” Ross says. There is hope, however: Ross tells Northern Express she just received word from the office of Senator Gary Peters that Michigan has received a sizable multi-year grant to help fight the disease.

Oak wilt

A worrisome fungus that attacks red oaks, oak wilt is spread through shared root systems and certain beetles, which carry spores that can attack healthy trees, especially through fresh wounds such as pruning cuts. Foreman says affected trees develop the fungus under the bark, which then goes through its sap system. Impacted trees will die in just a couple of months. The beetles also spread the disease through moving affected firewood. 

Ross says the impact will be devastating. “You don’t know it’s affected until it’s dead. Tears flow at site visits,” she says.

While the lattermost three invasive species portend huge changes in the forest environment, it’s not all doom and gloom. As an example, Ross points to the state’s ash trees. While the emerald ash borer destroyed most of the state’s ash trees before moving on, Ross says the remaining ash trees are slowly rebounding. “Research from MSU shows some of the most heavily impacted areas are showing signs of miraculous recovery,” she says.

She also says diversification will help mitigate the affects now and in the coming decades. She says introducing trees that will be winners as climate change warms the region will help. In particular, she cites white oaks, shagbark hickory, basswood, and hackberry as trees we can plant now to help offset the losses to come.

Despite the large infestations of loosestrife, milfoil, and others in many of the region’s waterways, Perrino says it’s important not to give up. Like Price, she says it’s imperative to continue both educate people and work to negate the impacts of non-native plants and animals. Whether you observe new growths of knotweed or baby’s breath and take the time to remove them or support continued research into means of treating these species, preserving the environment is critical for everyone.

It’s also critical to continue to research the problems posed by the different species. A project at Good Harbor is the use of Zequanox®, a U.S. EPA-registered molluscicide specific to zebra and quagga mussels. It is approved for use in open water lakes and has been safely used in multiple lakes across the Great Lakes region. The project is a partnership among more than a dozen organizations and educational institutions, including the University of Michigan, the University of Wisconsin-Milwaukee, EGLE, the DNR, and the National Park Service.


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