Purple loosestrife
Botanical Name
Lythrum salicaria
Family
Lythraceae (loosestrife)
Also known as
Bouquet-violet
Where is it originally from?
Europe and Asia
What does it look like?
Erect, hairy, summer-green perennial herb (<1-2 m, occasionally <3 m) with a taproot and fibrous roots that form dense surface mats and produce up to 50 stems per rootstock. Much-branched stems are 4-8 sided, pink at base and die off in winter. Narrow leaves (20-100 x 5-25 mm) are usually paired. Showy, densely hairy flowerhead spikes (20-25 cm long, Dec-Feb) are made up of purple-magenta flowers with 5-6 petals which are followed by blackish seed capsules (3-5 mm long).
Why is it weedy?
Rapidly invades damp ground and shallow water. Overtops native species with dense bushy growth, is long-lived and produces millions of long-lived, highly viable seeds from an early age. Tolerates hot or cold conditions and low to high nutrient levels in the water, but is intolerant of salt water.
How does it spread?
Seed is spread by the movement of water and contaminated machinery, soil, livestock and hay.
What damage does it do?
Forms massive, tall, impenetrable stands, excluding all other species. Destroys wetland and marginal habitats and food sources for many fish and bird species, and causes blockages and flooding.
Which habitats is it likely to invade?
Invades wetlands, lakesides, streams, swamps, bogs that are damp in winter and drier in summer, and creeps onto dry margins.
What can I do to get rid of it?
Start control work at margins to prevent further seeding, and work downstream in riparian areas where possible.
1. Physical removal: Dig out small infestations. Remove the entire plant and burn or dispose of to landfill.
Weedmat: kills whole patches. Start at top of infestation, leave 3-4 months.
2. Foliar Spray: IMPORTANT Purple Loosestrife is primarily an aquatic species that grows in riparian or wetland areas. Herbicides may not be used in aquatic areas where it may enter the water including in wetlands. Spraying recommendations are for terrestrial sites ON DRY LAND ONLY.
Apply glyphosate 360g/kg active inredient (10ml/L) + esterified seed oil adjuvant 5ml/L. Respray until eliminated.
OR Apply Triclopyr herbicide (600g/L active ingredient) at a rate of 6ml/L to thoroughly wet all parts of plant.
OR Apply Picloram/triclopyr herbicide (picloram 100g/l and triclopyr 300g/l active ingredient) at a rate of 6ml/L to thoroughly wet all parts of plant. Follow up 3-monthly.
4. Lower water level if possible and mechanically remove.
5. Raise water level if possible for 2-3 weeks to drown the weed.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and directions for the purchase, use and storage of the product, are followed and adhered to.
What can I do to stop it coming back?
Plant tall trees adjacent to infested margins to shade out weed, and deepen water if possible to prevent growth.
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