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Beetles Help Take a Bite Out of One of the Word’s Most Aggressive Weeds

Over the past decade, beetles have taken a major bite out of purple loosestrife, one of the world’s most aggressive weeds.

Featured on “the most noxious weeds” list in 33 states, purple loosestrife (Lythrum salicaria) is especially a problem in the Midwest where it clogs wetlands and waterways. In the early 1990s, researchers in Minnesota were among the first to try a biological-based approach for beating back the weed. They released two types of loosestrife beetles (Galerucella calmariensis and Galerucella pusilla) that love to munch on purple loosestrife foliage.

Just two years later, University of Minnesota weed scientists Drs. Jeanie Katovich and Roger Becker, and Dr. Luke Skinner of the Minnesota Department of Natural Resources noted a significant reduction in purple loosestrife biomass and seed production. And by five years after the initial release of the beetles, they were finding a dramatic reduction in loosestrife stands.

The successful trial helped pave the way for beetles to be released across 13 Midwest and Northeast states. Small “starter kits” of caged beetles were provided to agricultural inspectors, department of transportation staffers, wildlife managers, school children and members of 4H and garden clubs, who helped to rear and distribute the insects in weed-infested areas.

To date, more than eight million beetles have been released in Minnesota alone. Similarly, Nebraska has released approximately 500,000 beetles per year since 1997 to tackle loosestrife infestations along the Niobrara and Missouri rivers and in the wetlands surrounding Lewis and Clark Lake. “We’ve been able to reduce purple loosestrife infestations by about two-thirds in just eight years,” said Dennis Daum, the U.S. Army Corps of Engineers park ranger who helped to rear and release 100,000 beetles a year in the fragile backwaters of Nebraska’s Lewis and Clark Lake. “Many of the plants that remain are severely stunted and aren’t vigorous enough to compete with native vegetation.”

Dr. Stevan Knezevic of the University of Nebraska says the beetles not only stunt loosestrife, but also cause a delay in the time of the invasive weed’s flowering by stripping away its canopy. That means there is much less time for loosestrife to produce seeds and spread. It also means that less herbicide is needed to control the weed. In Minnesota for example, annual expenditures for herbicide management of loosestrife decreased ten-fold from 1989 to 2003, mostly due to the success of the beetle program.

“Beetles are another weapon in our arsenal for combating loosestrife, especially when used in combination with other weed control methods,” said Lee Van Wychen, director of science policy for the Weed Science Society of America. “As a result, we’ve been able to make great strides in preserving our wetland habitats from one of the world’s most aggressive weeds.”

The Minnesota research that helped to establish the successful beetle biocontrol program was a cooperative effort involving scientists and managers from the University of Minnesota, Minnesota Department of Agriculture, Minnesota Department of Natural Resources, local park lands, Cornell University and CABI Bioscience of Delémont, Switzerland.


Purpole Loosestrife Before and After Introductions of Beetles.
– Click on thumbnail to view larger image.

Purple loosestrife in bloom – Photo University

Close-up of purple loosestrife flowers – Photo University of Minnesota

Early season canopy defoliation by beetles. Photo by Stevan Knezevic, University of Nebraska

Canopy defoliation from May, and new growth in June-July. Photo by Stevan Knezevic, University of Nebraska

  • With showy pinkish-purple flowers, loosestrife has been cultivated both as an ornamental flower and as a medicinal herb.
  • It is considered a serious threat to waterways and wetlands in temperate climates across the U.S. and Canada.
  • A single purple loosestrife plant can produce between 100,000 and 2.5 million seeds that are small, lightweight and easily disbursed.
  • Loosestrife can displace native vegetation, disrupt wildlife habitats, clog irrigation ditches and negatively impact water quality.
  • For more information on purple loosestrife and other invasive plants, visit http://www.wssa.net.

About the Weed Science Society of America:
The Weed Science Society of America, a nonprofit professional society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Weed Science Society of America promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, and fosters awareness of weeds and their impacts on managed and natural ecosystems. For more information, visit http://www.wssa.net.