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Purple Loosestrife

Purple Loosestrife

Purple Loosestrife

(Lythrum salicaria)

Priority: -  Control

Tags: Aquatic | Biocontrol

Identification and Reproduction

Identification

  • Tall, perennial, wetland herb that grows up to 3 meters tall from  square, smooth woody stems.
  • Leaves are opposite, dark green, and lance-shaped.
  • Spike of purple flowers found at the upper end of stems. Flowers have 5-7 petals which appear from July through October.

 

Reproduction

  • Perennial plant that reproduces by seed and root fragments.
  • Each plant is capable of producing up to 2.5 million seeds.
  • Seeds are easily dispersed by wind, water, wildlife, and humans.

Habitat & Ecology

Thrives in open riparian areas, ditches, ponds, and wetlands. Moisture is essential for its growth and reproduction. 

Impacts

Ecological: 

  • Forms dense stands on aquatic sites, outcompeting and replacing native wetland species. 
  • Purple loosestrife invasions displace wetland wildlife by removing of native food sources and nest habitat. 
  • They also block irrigation canals and degrade water passages. 

Management

Mechanical/Manual Control:

Hand pull or dig the plants out and ensure that all root fragments are removed to prevent re-growth.

Biological Control:

  • For large patches, there are relatively effective biocontrol agents. For example these beetles, Galerucella calmariensis and G. pusilla, feed on the plant stems in their larval stage. 
  • Hylobius transversovittatus is a root feeding weevil. 
  • It will take a minimum of 2 years to defoliation to kill the plants. 
  • Please see the Best Management Practices for purple loosestrife for more information on biolgoical management (page 10). 

For alternative planting options to purple loosestrife download the ISCBC's Grow Me Instead brochure (pg. 43 and 44).

Resources

Download the Metro Vancouver's Best Management Practices for purple loosestrife here. 

Header photo (Manfred Heyde).