Weed Watch – Purple loosestrife

 

Purple loosestrife

Purple loosestrife

Purple loosestrife was previously sold as a garden plant but it is has been declared an unwanted organism in New Zealand by the Biosecurity Act 1993 and consequently is banned from sale, propagation or division.

 

Characterised by its pretty, tall, purple-pink flower spires, the plant can grow as high as three metres and have as many as fifty stems per plant. It flowers from December to February and it can produce over two million seeds per plant per year – and most seeds can last several years. The seeds are dispersed by water but may also be spread by birds and by people sharing garden cuttings.

 

Purple loosestrife thrives in damp places, particularly around wetlands, garden ponds or along river and lake margins. Once established, it quickly forms a dense stand that excludes most other vegetation. It also has the potential to clog waterways and impede drainage

Within the Te Waihora catchment, purple loosestrife is found in some private gardens and along many of the drains that run into the Halswell River. The Department of Conservation and Environment Canterbury control these areas every season with glyphosate.

 

Purple loosestrife on a stream bank.

Purple loosestrife on a stream bank.

On occasion the cut and paste technique has been used. Since starting control of purple loosestrife in 2002, its density within the area has reduced dramatically. This year flooding within the Te Waihora Catchment has made control more challenging, as plants were partly submerged along water courses making the second round on control unfeasible. This is the first time since control on the plant began that this situation has arisen.

 

All known active purple loosestrife sites are visited and controlled where necessary – within Canterbury every year in a collaborative approach between Christchurch City Council, The Department of Conservation and Environment Canterbury.

 

If you have seen purple loosestrife in Canterbury, or think you have it in your garden, you can contact Environment Canterbury Biosecurity via Customer Services on 0800 324 636 or email ecinfo@ecan.govt.nz and leave your details with your name, contact number and location of sighting. A good identification tip is to roll the stem between your finger and thumb. Purple loosestrife stems are distinctively angled rather than round.