Purple loosestrife

Purple loosestrife

Fact Sheet


Latin Name: Lythrum salicaria

Origin:  Eurasia

Physical Description: It is a perennial herb from a rhizome. The stems are woody and square-ish with 4 to 6 sides. Mature stems can grow as tall as 2m tall. Its narrow and stalkless leaves are opposite, lance-shaped and sometimes covered in fine hair. Flowers appear along dense spikes that have showy reddish-purple flowers. Each flower has 5 to 7 petals.

Habitat: It prefers moist highly organic soils that have neutral to alkaline pH. It can tolerate partial shade, calcareous and acidic soils and shallow standing water. Ideal habitats include areas such as wetlands, lake and river shores, ditches, marshlands, and riparian meadows.  If it is already well established, it can survive on drier soil types found in pastures or rangeland.

Impacts: It invades riparian areas which can displace valuable habitat and biodiversity. Dense infestation can block canals and water flow resulting in flooding. It can also reduce available forage for wildlife and livestock and reduce palatability of hay that contains it.

Reproduction:  It reproduces by both seed and vegetative root fragments. One plant can produce up to 2.5 million seeds. Each seeds can remain dormant in the soil for up to 20 years. Seeds are mainly dispersed by water however can also be moved around by wind, wildlife, transportation, development, and other human activities. Root fragments can be transported through contaminated soils and other material, such a gravel.

Management Options

Mechanical:  Young plants can be effectively hand pulled. All plant material, particularly the root crown, should be removed to prevent re-sprouting. Shoots of mature plants can be cut to reduce seed production.  Mowing can help reduce seed production but is typically impractical due to the preferred wet habitat of the plant.  Tilling is not recommended as fragments or root tissue is likely re-sprout and spread.

Chemical: Several herbicides with the following active ingredients can control Purple Loosestrife: Imazapyr, Triclopyr, Glyphosate, and Metsulfuron.  For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions.

Biological: There are several foliar feeding biocontrol agents available:

Additional Resources:

Alberta Invasive Species Council’s Purple Loosestrife Factsheets

Provincial Biological Control Agents and Host Plants-Online Resource


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