Aggressive, Magenta Invader Crowding Out Native Plants and Animals

This time of year, area residents can see long-stemmed, bright purple flowers growing along ditches, lakes, ponds and other wetlands. The purple blossoms might look colorful and attractive, but they actually belong to an aggressively invasive plant from Europe that is taking over American wetlands and displacing native plants and animals.

It's purple loosestrife, which reached the U.S. in the early 1800s via European ships. The plant came to America as a contaminant in ship ballasts, which were filled with soil to add weight and make the ships more stable.

And people took it along specifically as an herbal treatment for dysentery, wounds, bleeding and diarrhea (invasiveplants.net). It also was used for ornamental purposes, according to the Plant Conservation Alliance's Alien Plant Working Group, which labels it as one of its "Least Wanted."

One plant can produce millions of seeds each year, and it's illegal to sell purple loosestrife in Michigan, said Laurel Malvitz, resource steward for the Michigan Department of Natural Resources' (DNR's) Stewardship Unit.

Purple loosestrife seeds spread by water and in mud that sticks to people and animals. As a result, it now grows around the continental U.S. — except for Florida, experts say — and into Canada. Purple loosestrife is a perennial that grows back each year, in a wide variety of habitats. It can be 4-10 feet tall, has lance-shaped leaves and produces its bright, magenta flowers throughout the summer.

The purple-flowered plant crowds out native plants that provide food for insects, for example. And some native insects' larvae can only survive on certain plants.

"It has ripple effects on many different species," she said.

Wetlands are very diverse, important systems, with very diverse sets of plants, Malvitz said. They provide habitat for insects, animals, birds, frogs, toads and turtles.

"With purple loosestrife, you are missing out on lots of really important parts of the ecosystem," she said.

To combat the plant, people have imported Galerucella beetles from Europe. Scientists have tested the beetles to prevent unwanted effects on native plants, a Minnesota Sea Grant spokesperson states.
Galerucella beetles, a natural enemy of purple loosestrife, are being used in Michigan, Malvitz said. They are very small, and people sometimes confuse them with much larger, irridescent Japanese beetles. Galerucella beetles are much smaller.

"Unless you were looking for them, you probably wouldn't see them," she said.

These beetles are doing a pretty good job of controlling purple loosestrife. Volunteers collect Galerucella beetles in the spring, re-releasing them at other locations to help spread the beetle populations. This redistribution takes place in late May to mid-June, she said.

There are volunteer opportunities to help the DNR with this in the spring, Malvitz said. In addition, volunteers are needed currently, to scout the amount of purple loosestrife growing in state parks. Those who would like to help can contact her at (248) 359-9057.

For those who would like to control purple loosestrife on their property or in a certain area, Malvitz suggests removing the flower heads, which will help keep it in check. "The best thing you can do is prevent it from going to seed," she said.

If it's a small patch, people could try digging it out. This might be difficult, though, since the plant has a pretty extensive root system, she said.

And using an herbicide could be harmful, unless it's specially labeled for use in wetlands. Herbicides can cause damage to plants and animals in a wetland.

"They could have negative impacts on the species they are trying to protect," Malvitz said.