Purple invader on the loose

One of the world’s Top 100 invasive species is at large in the Wellington region and Greater Wellington Regional Council wants your help to find more sites of it.

Purple loosestrife (Lythrum salicaria) has become one of the worst weeds in the United States of America where it has displaced other plants and taken over large areas of productive land.

“We know of several large areas of purple loosestrife and can see what it is capable of doing. There is no reason, that if it is left to its own devices, it will not take over large areas of New Zealand,” says Biosecurity Officer Ben Winder.

Purple loosestrife was sold as a garden plant in the past but it is now banned from sale, propagation and distribution in New Zealand.

“If you have an older garden you may still find purple loosestrife growing in it” says Mr Winder. “It is not constrained by fences and may be spreading without you being aware of it” It thrives in damp areas such as wetlands and around ponds and lakes but can grow just about anywhere it is tolerated.

Purple loosestrife can grow up to three metres tall with stiff upright stems which are square in cross-section. It has showy purple spikes of flowers from December through to March and the whole plant dies off in the colder months and re-sprouts when it warms up again.

It has huge seeding capability producing over three million seeds per plant which are easily spread by birds, wind, water and machinery such as mowers or harvesters. It can also spread by way of fragments of the stem and the root which can re-sprout forming new plants.

“Currently, the only sites of purple loosestrife we know about are in isolated pockets of the Kapiti Coast and the Wairarapa but it could be on land in any part of the Wellington region,” says Mr Winder.

If you think you have seen purple loosestrife phone Greater Wellington Regional Council on 0800 496 734 and we can come and check it out. Alternatively email pest.plants@gw.govt.nz or check out the pest plant pages at www.gw.govt.nz