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Voyageur's Best Generally Speaking Columns of 2003

Purple Loosestrife

The 'invasion' of...
by Mary Stefanski  |  August 26, 2003

What a beautiful plant! Generally the first words spoken when someone sees purple loosestrife. Yes, it is beautiful, but it is also detrimental to the lakes and wetlands where it takes up residence. Purple loosestrife is an ‘invasive’ which simply means it invades areas, taking over entire wetlands and an ‘exotic’ meaning it comes from somewhere else. In the case of loosestrife that somewhere else is Europe.

Purple loosestrife is a perennial plant that was brought to the United States for gardens and by bee-keepers who wanted their honeybees to feed on the plant’s nectar which is said to produce the best tasting honey. Seeds from the plant were also accidentally brought to the states in the ballast of European ships.

The plant quickly spread across the country and at one time was a top-selling greenhouse plant. Eastern states were the first to experience what happens when the plant ‘escapes’ into the wild. Hundreds of thousands of acres of wetlands were quickly covered by a sea of purple.

Beautiful, yes, but the loosestrife is able to out-compete with the native plant species. This eventually leads to a mono-culture, or single species habitat which is both un-natural and unhealthy for the ecosystem. It was also found that native wildlife species don’t readily use loosestrife for food or cover.

Purple loosestrife spreads by both its root system and seeds. Each mature plant produces up to two million seeds each year! Early efforts to control the plant focused on using herbicide applications. This method proved both time-consuming and expensive. Today, biological control is the buzz word. Biological control involves finding a natural predator. In the case of loosestrife, this meant going to Europe and finding insects that feed on the plant. These insects were then studied to learn which ones actually destroyed the plant. These were then rigorously tested for a period of 10-years to ensure that they didn’t also attack other wetland plants and/or agricultural cash crops.
In the end, five of over 100 species of insects were cleared for release in the United States and Canada.

The beetles which were chosen to head-up the attack on loosestrife were brought into the U.S. as brood stock. If a lake or wetland becomes infested with loosestrife, brood-stock insects are raised in captivity to produce enough off-spring to take to the site and release. In Minnesota, the leaf-eating beetle and the root-mining weevil are most commonly used. While the bugs will not eliminate the loosestrife, they will control it to a level where native plants can again flourish. In Aitkin County, releases have been done at Long, Van Duse, and Farm Island Lakes and near Red Top.

Everyone can help keep loosestrife from spreading through the area lakes, streams and wetlands.

First, don’t plant it in your garden. While it’s beautiful and easy to care for, it is classified as a noxious weed, making it illegal to propagate. Second, if you see a loosestrife plant, pull or dig it up, put it in a garbage bag until it is dry and then put it in the trash.

If pulling or digging aren’t an option, cut the flowering heads off and destroy them so the plant can’t produce seeds. If you discover a large infestation, biological control may be the best answer. Large infestations should be reported to the Minnesota Department of Natural Resources.

The good news is there isn’t a lot of loosestrife growing in Aitkin County. We have many native plants growing that could be confused with loosestrife. Fireweed is a common plant in the road ditches. It is pink to red in color and the flowering head has the shape of a Christmas tree. Other plants which have similar coloration are milkweeds, vervain, gay feather and many others. If you are unsure of a plant’s identification, cut a sample and bring it to your local DNR office or the Refuge.

If you would like more information about purple loosestrife, please contact the Rice Lake National Wildlife Refuge at 218-768-2402 for a full-color brochure describing the plant and control methods.

This article first appeared in the August 26, 2003 issue of the Voyageur Press.