Mature purple loosestrife
History  Impacts LRCA Action Loosestrife-Eating Beetles
Control Options Do Not Plant Identification Reporting Form

Purple loosestrife (Lythrum salicaria) is not a native species; it was introduced to North America in the early 1800's from Eurasia. Settlers imported plants for their gardens and seeds were present in soil used for ballast on ships.

Since those early beginnings, purple loosestrife has found its way into wetlands in nearly every Province and State in North America. In 1990, Purple Loosestrife was first documented in the Thunder Bay area. Since that time it has been found in several locations in the City and surrounding municipalities.

Lythrum is a very hardy perennial plant that can outgrow cattails, sedges, rushes and the other native aquatic plants on which wildlife depends. The roots of loosestrife form a dense mat that blocks other plants from growing up. Eventually, it chokes out the other vegetation and soon becomes the dominant species. In marshes where a loosestrife seed source is present, the plant can be expected to colonize exposed areas in high densities with great speed.

A change in the diversity and type of plant species threatens the hundreds of species of plants, birds, mammals, reptiles, insects, fish and amphibians that rely on healthy wetland habitat for their survival. For example, cattail stands are home to Muskrats and a variety of nesting birds, such as Marsh Wrens. Purple loosestrife does not provide the necessary shelter and food sources.

The dense loosestrife roots also clog water channels in the marsh. These are places where fish would come in to spawn, ducks would feed, nutrients would flow and insects could hide and feed along the edges.

Thousands of hectares of wetlands, marshes, pastures and riparian meadows are affected in North America each year, with an economic impact of millions of dollars. Roadside and agricultural drainage ditches can be affected, resulting in extra costs for more-frequent cleaning.

There are several management techniques for controlling purple loosestrife. The L.R.C.A. recommends hand pulling as the most effective method where appropriate. Herbicides are not recommended, as they will effect other species.

Hand pulling:

  • Effective and selective
  • Best done while plant is in flower (i.e. July and August) and before it goes to seed
  • Loosen soil with garden fork or shovel; grasp plant firmly near the base and pull evenly to avoid detachment
  • Plants should be dried, burned or put in garbages and disposed of in a sanitary landfill where there is no chance of spreading
  • Check annually for new plants
  • In 2006 and 2007, Ontario Rangers from Sleeping Giant Provincial Park, Nipigon and Thunder Bay removed over 12-tonnes of Purple Loosestrife from patches along Oliver Road in Oliver Paipoonge and Lakeshore Drive in Shuniah Township. Large patches remain in each area.


  • Used to contain large populations of loosestrife, by reducing stem numbers and seed production
  • Care must be taken to gather up the cuttings
  • Repeated cuts are required to eliminate the plant from the site

Galerucella is a loosestrife-eating beetle Biological Control:

  • A long-term solution that will not completely eradicate, just reduce density of loosestrife
  • Involves releasing European insects that are predators of loosestrife
  • Thorough scientific screening of potential species has resulted in a few being approved for release
  • LRCA released Galerucella beetles at two sites near Thunder Bay in 1997 and at three sites near the Kam River in 2003. In 2007 beetles were released along the Thunder Bay Expressway near Dawson Road.
  • At a release site east of Thunder Bay, the beetles dramatically reduced loosestrife plants to short withered stems within a few years.


  • In most areas is not permitted for general usage
  • Must be used with extreme caution, because herbicides are non-selective and will hurt the nearby vegetation
Do not plant any form of Purple Loosestrife
Purple loosestrife is available for sale. Do not buy it or plant it in your yard. New plants can grow from pieces or from the seeds of loosestrife. Although it is beautiful looking, even sterile hybrids of loosestrife can cross-pollinate with wild Purple loosestrife to produce seeds. If you have loosestrife in your garden, please pull it out and do not share it with friends.
How to Identify Purple Loosestrife
Citizen and staff reports indicate that the main growing sites are:

  • Along the Kam River between James St. and Old Fort William
  • Montreal St. and Neebing Ave.
  • Along Oliver Road, west of the City
  • Lakeshore Drive in Shuniah, between Amethyst Harbour Rd. and Birch Beach Rd.
  • Several smaller sites scattered across the watershed
More reports are received each year regarding loosestrife sites.

Report your loosestrife sighting using our Mail-in Form or On-line Form

Report a purple loosestrife growing site:

On-line form    Mail-in form

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Lakehead Region Conservation Authority
P.O. Box 10427; 130 Conservation Rd.
Thunder Bay, ON  P7B 6T8 (Canada)
Telephone:(807) 344-5857  Fax:(807) 345-9156