EMERGENCY: There is currently 1 INCIDENT.

Purple Loosestrife - Lythrum salicaria

Description: Purple loosestrife is a perennial forb or semi-shrub growing up to 3.5 m in height in a wide range of wet to moist habitats (Mullin 1999). This species was introduced into North America from Europe or Asia as early as the 1830s and was first reported on the west coast of North America in the 1940s.

Type: Perennial

Habitat and Impacts: Loosestrife is very invasive and can displace native vegetation in riparian areas, reducing habitat quality, water flow, and forage potential. Purple loosestrife can form thick monoculture stands where it becomes established and reduces habitat values and plant and animal diversity. Water flows can be impeded when infestations occur in streams and drainage ditches.

Method of Spread: Purple loosestrife can reproduce by seed or vegetatively. Root or stem fragments can also form adventitious roots and develop into new plants. Seed production is high with up to 300,000 seeds per plant. Seeds are spread mainly by water, but also by animals and humans. Seeds remain viable in the soil or sediments for up to 20 years.

Location: Two records of purple loosestrife are found in the Cariboo Chilcotin Coast, one on the Nazko Road north-west of Quesnel and the other at Alexandria.

Management Options:

Mechanical: Hand-pulling new sites with young plants is often the most effective treatment. Complete removal of all roots and seeds is not possible with older plants, so eliminating seed production is needed to prevent seeds from being spread to other suitable sites.

Chemical: Herbicide use is often not possible in the wet habitats purple loosestrife occupies.

Biological: Three biocontrol agents have been released in British Columbia and have resulted in decreased vigour and seed production along British Columbia’s coast. Infestations need to be large enough to support a biocontrol agent population and there are insufficient plants in the Cariboo Chilcotin Coast to warrant a biocontrol release.

CCCIPC Priority and Treatment Strategy: Priority 1 (new invader) Reducing bare soil on wet sites is the best method of preventing new occurrences of purple loosestrife

Treatment Options:

Local Level - Hand pull young plants, cut to eliminate seed production for larger and older infestations. Do not use in ornamental plantings.
Landscape Level - Cut to eliminate seed production.


Randy Westbrooks, U.S. Geological Survey, Bugwood.org

Purple Loosestrife infestation

Purple Loosestrife flower

Steve Dewey, Utah State University, Bugwood.org

Purple Loosestrife plant


Invasive species profile taken from the Cariboo Chilcotin Coast Invasive Plant Committee Invasive Plant Regional Strategic Plan

Page last modified: October 30, 2018 09:44:02 PDT