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Controlling Purple Loosestrife Naturally

Purple loosestrife flower“Beauty is only skin deep,” is a phrase that has been around a long time and one that is very applicable to purple loosestrife, a plant which conceals its menacing nature.

Loosestrife’s rows of pretty purple blooms can seem appealing while it systematically crowds out native vegetation, effecting wetland biodiversity and, in turn, wetland wildlife. Purple loosestrife provides little or no value as a habitat or food source for wetland animals. For example, loosestrife will drive out native wetland cattails, which are important to nesting waterfowl.

The plant is widely distributed throughout the United States and is becoming more abundant in the Dairyland service area, especially along the Mississippi River in Minnesota, Wisconsin and Illinois.

Beetle mania

beetles

Dairyland’s commitment to environmental stewardship expanded in 2002, as action to eradicate purple loosestrife was taken at an area adjacent to our Flambeau hydroelectric facility near Ladysmith, Wis.

To combat this exotic invader-native to Europe and Asia-Dairyland released approximately 4,000 Galerucella beetles at a purple loosestrife stand near the Flambeau Station in July 2002. Dairyland purchased the beetles from New York’s Cornell University and released them as part of the Wisconsin Department of Natural Resources’ purple loosestrife biological control program.

Using beetles provides an environmentally safe alternative to the use of herbicides, the conventional method used to control this exotic plant. Dairyland will monitor the beetles’ progress over the next few years. Dairyland Environmental Biologist Brad Foss said the cooperative has been monitoring the beetles’ progress and has seen decreasing loosestrife density. Dairyland’s new license for the Flambeau facility requires we monitor and control purple loosestrife, as we have already been doing. Additional beetles will be introduced in 2005.

How do the beetles work?

The beetles munch on the plant’s buds, leaves and stems. Like purple loosestrife, these beetles are native to Europe and feed on the plant there. As Foss says, "We are using one exotic to control another exotic."

Unlike the importation of other exotic insects used to control unwanted pests, this beetle is not anticipated to become a problem in itself. The beetles only eat purple loosestrife; once they have decimated the plant, they starve. Studies have shown they have no negative effect on native plants or agricultural crops.

The beetles have a one-year life cycle. They burrow in topsoil at the end of summer and lay eggs in the spring. Although the beetles’ life is short, they are prolific breeders; which will keep supply going from year to year.

Purple loosestrife’s economic impact

The negative economic effect of purple loosestrife in the Dairyland service area can be substantial. “The loss of waterfowl habitat decreases acreage available for hunting, affecting both the hunters and their financial contribution to the communities they visit,” said Bob Drieslein, Winona (Minn.) district manager of the U.S. Fish and Wildlife Service.

“Once the aggressive loosestrife establishes in drainage ditches, more frequent cleanout will become an additional financial burden to farmers and other landowners. The presence of loosestrife may lower land value and could have serious effects on the resale,” he added.

A challenging predator

“Loosestrife is displacing the native wetland plants at an alarming rate,” notes Brian Pember, biological technician with the Winona District of the US Fish and Wildlife Service. “When the conditions are right, a small isolated group of loosestrife plants can spread and cover a marsh in only one growing season. Once established, loosestrife is difficult to control. A single, mature plant may produce in excess of 100,000 seeds which are small in size and easily spread by wind.”

The shallow, woody root system forms a dense mat, making adult plants difficult to pull. If the entire root is not taken, it will resprout. If plants are mowed the stem pieces will actually send out new roots, eventually become anchored and begin new colonies.

Seeds remain viable when submerged for years, waiting for the opportunity to sprout during a dry summer. They have the capacity to completely replace native vegetation.

More about purple loosestrife

Purple loosestrife has devastated wetlands across America and has no predators natural to our region of the world. By bringing in the beetle, its European predator, it is predicted that the plant will be reduced by 90 percent over 90 percent of its present range. (Cornell University)

“Because of its beautiful color, a purple loosestrife plant may seem acceptable or even desirable to some,” said Drieslein. “Many people who are unaware of the plant’s invasive nature have propagated specimens from a nearby wetland into their own backyard marsh and the spread continues.”

The aggressive plant has little to no wildlife value. Songbirds do not make use of the small, hard seed. Muskrats require cattails to build their homes and they show a preference for cattail over loosestrife for food. Waterfowl, especially ducks, avoid wetlands that have become dominated by loosestrife. In addition, overall waterfowl production is decreased as habitat is eliminated.