Bringing Invading Plants Under Control with Machines, Poison and Bugs

By Kevin Bunch, IJC

purple loosestrife
Purple loosestrife grows alongside a path in the Cooper Marsh Conservation Area in Cornwall, Ontario, near the St. Lawrence River. Credit: Saffron Blaze

The term “invasive species” doesn’t just include animals. Invasive plants also can upset local habitats and food webs, threatening ecosystems along the Great Lakes shorelines and inland waterways thanks to a lack of predators and prodigious methods of reproducing.

While non-native plants are nothing new to the basin, invasive species differ in how quickly they can spread out of control according to Beth Clawson, natural resources educator with Michigan State University Extension. For example, Clawson said a non-native butterfly bush brought in for a garden isn’t going to become a nuisance and overtake everything else, but bringing in an invasive plant like purple loosestrife, which can produce more than 2 million seeds a year, can quickly see the available space for native species spiral out of control.

Non-native plants have been in the Great Lakes basin for decades, but only a relatively small number have been deemed invasive. To be considered invasive, a species must threaten the diversity or abundance of native species, or the ecological stability and water quality of infested waters. The US National Oceanic and Atmospheric Administration counts 58 non-native plants in the basin, while the US Environmental Protection Agency considers seven of those to be invasive. The province of Ontario has 27 aquatic invasive plants listed as either already in the region or on the watchlist in case they expand into the Great Lakes.

“That’s why (purple loosestrife is) invasive,” Clawson said. “They’re hard to kill, they’re broad spectrum in the sense they can live in a large variety of environments, they don’t have (native) predators, and they come to reproduction (age) fast and reproduce quickly.”

Purple loosestrife quickly crowds out native wetland plants like wild rice, destroys fish and wildlife habitat, and also survives on drier land. Since the 1990s, the Canadian and US governments have released natural predators – European beetles and weevils – to control severely infested areas without damaging native plants in the process. Biological control has proven successful; though purple loosestrife will not be completely eliminated with this control method, its abundance can be greatly reduced to the point where it is only a small component of the plant community.

Besides purple loosestrife, Phragmites, or the common reed, has become an increasingly problematic invasive species according to Kyle Borrowman, terrestrial invasive species outreach liaison with the Ontario Federation of Anglers and Hunters. Phragmites has become a menace along the coastlines of Lakes Ontario, Erie, Michigan and Huron, and is slowly making its way north; large stands have already been found as far as Green Bay on Lake Michigan and Georgian Bay on Lake Huron. Like purple loosestrife, Phragmites can choke out native plants in coastal zones, reducing biodiversity and destroying habitat used by animals. Borrowman said they also can pop up in irrigation canals, degrading farmland, and in strips of land along roadways, reducing visibility. Dead stalks are a fire hazard, particular as stands become thick. Unlike purple loosestrife, no biological control methods are currently available to deal with Phragmites, Borrowman said.

tall phragmites
A photo showing how tall Phragmites can grow. Credit: Ontario Phragmites Working Group

That isn’t to say there aren’t other methods of dealing with the plants. Both invasive species are vulnerable to herbicides, though Ontario currently does not allow their use over water except in specific circumstances. Mechanical removal, hand-pulling and controlled burns are viable methods to remove Phragmites, while hand-pulling, herbicides, biological control and lengthy flooding can help eradicate purple loosestrife. Ideally, landowners and management officials can use a combination of multiple techniques to make sure these plants are cleared out.

Phragmites can be identified as a tall beige plant of up to five meters (16 feet), single stalked with narrow, long bladed leaves, and a seed head at the top of the plant in the latter part of the growing season. It also bears some resemblance to a native reed, though the native reed does not grow as tall or push out other native plants. Michigan Sea Grant reports that a mature purple loosestrife plant can be as high as six or seven feet (two meters) high and about four feet (1.5 meters) wide, with 30-50 stems growing from a common root ball. It also has multiple purple flowers sticking out from it during the flowering season of July-August, Borrowman said. Both species can sometimes be found as garden options, but Borrowman suggested that landowners who want to decorate their waterfronts consider native plants like common cattail, native reeds or hard stem bulrush.

Inland waterways face other kinds of invasive species, like hydrilla, Eurasian water milfoil, water soldier, starry stonewort and European frogbit. Much like purple loosestrife and Phragmites, these plants reproduce quickly and in multiple ways, Clawson said, growing from seeds or cloning through roots and cuttings. They can even be transported accidentally by watercraft when parts get cut off and are carried to a new water body or location. Clawson recommends boaters follow boat-cleaning and quarantine procedures before entering new water bodies to prevent the plants from spreading, and landowners consider native plants for erosion control, gardening and restoration of inland waterways.

If someone spots an invasive species, Borrowman said they should contact the state or provincial regulatory agency that covers invasive species, such as the Michigan Department of Natural Resources, the Ontario Ministry of Natural Resources and Forestry, or the New York Department of Environmental Conservation. Michigan State University released a field guide to identify invasive aquatic plants in the region to make it easier to pick out these species. The Ontario Phragmites Working Group also has a toolkit for landowner’s proposing to remove invasive Phragmites from privately owned property.

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

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