Lythrum salicaria

Purple loosestrife

Family: Lythraceae

Origin: Africa, Australia, Eurasia

Regional Pest Management Plan (RPMP) status

  • National Pest Plant Accord Species

View more about the RPMP statuses

General description

Erect, perennial herb < 3 m tall. Roots are fibrous and form dense surface mats. Stems are usually many-branched and square. Leaves are < 12 cm long, lanceolate-ovate, narrow, opposite or in whorls and clasped around the stem. Flowers are purple and borne in dense, < 25 cm long flower spikes in December-February. Seeds are minute, numerous and borne in blackish capsules.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell purple loosestrife. As purple loosestrife is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.


Still or slow-moving water bodies, wetlands, riparian margins, lakes, ditches, reservoirs.


Seeds dispersed by wind, water, waterfowl and soil movement. Vegetative spread from root fragments. Human-mediated dispersal through dumping of garden waste, deliberate plantings and movement of contaminated machinery, vehicles and clothing.

Impact on environment

Forms dense stands, outcompeting and displacing native vegetation. Impedes waterfowl and access to waterways.


Site Management

Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Recommended approaches

Physical control

Method: Dig out.

Plant parts requiring disposal: All parts.

Disposal options: Remove to greenwaste or landfill if practical.


Biocontrol is currently not available for this species.

Community agrichemical control recommendations

No qualifications: Foliar spray with 100ml glyphosate green per 10L of water.

Certified Handler/Experienced agrichemical user: Foliar spray with 100ml glyphosate green per 10L of water and 20ml penetrant.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

A field of purple loosestrife.
An upright perennial herb that can grow up to 3m tall. Plants have dense fibrous roots that form surface mats preventing other plants from growing.
Photo credit: Paul Champion, NIWA
Close up of a purple loosestrife.
Stems have a distinctive square shape and are red and green coloured. Leaves are long and skinny and can grow up to 12cm long.
Photo credit: Paul Champion, NIWA
Close up of the bright flowers of purple loosestrife.
A garden favourite due to its tall stems of purple flowers. Flowers appear across all summer months and produce masses of tiny seeds that can be shaken free by the wind.
Photo credit: Paul Champion, NIWA