Look out for Loosestrife

Environment Canterbury is asking Cantabrians in both urban and rural areas to be on the lookout for the invasive weed Purple Loosestrife.

Purple Loosestrife produces over 2 million seeds per plant every year. Because it produces so many seeds once it has established, it is able quickly to form a dense stand that excludes most other vegetation.

Loosestrife seeds disperse by water, and may also spread by wind, birds and machinery. It is one of the worst agricultural and environmental weeds in North America, where it has invaded large areas displacing other plants.

Graham Sullivan, Environment Canterbury Regional Manager Biodiversity and Biosecurity, said so far there were very few places in Canterbury where purple loosestrife was growing in the wild. “However, we all need to be vigilant,” he said. “Purple Loosestrife has the potential to do the same damage in New Zealand as it has in North America if it is not kept under control.”

Environment Canterbury, with the support of the Department of Conservation and Christchurch City Council, has been controlling all known sites annually for several years. 
“We want to make sure we are not missing any sites so we are asking for the public’s help in letting us know if they have seen it,” Mr Sullivan said.

Purple Loosestrife can be found in home gardens and is at its invasive worst around waterbodies. It can grow up to 3 metres high with up to 50 stems per plant. It flowers from December to February with showy spikes of purple flowers at the end of its stems. The plant dies off in winter and re-sprouts in spring. 

“A good identification tip is to roll the stem between your finger and thumb; Purple Loosestrife stems are distinctively angled rather than round,” said Graham Sullivan. “The individual flowers on the spikelet have 5 or 6 petals each - which makes it different from Purple Lineria, a plant it commonly gets confused with which is much smaller with purple pea-shaped flowers.”

If you think you have seen Purple Loosestrife contact Environment Canterbury Biosecurity via 0800 324 636 (0800 EC INFO) or email ecinfo@ecan.govt.nz and provide your name, contact details and location of sighting.