Weedspotters find nasty new pest in New Zealand

A nasty weed never seen in New Zealand before has been found on Auckland's North Shore by a member of a new weed-spotting network.

Auckland Regional Council (ARC) launched its Weedspotters initiative in June this year to encourage people in the community to be on the lookout for new and emerging weed species, and it has already paid off.

A North Shore "spotter" has reported an infestation of knotweed in Glenfield that has been identified by Landcare Research as Persicaria chinensis, or Chinese knotweed. This weed has never before been recorded in New Zealand.

"This is a really good example of how people in the community can help us fight weeds," says Vivienne Lepper, ARC Biosecurity Officer.

"If we know where a weed is, we can do something about it. Chinese knotweed is a known pest plant in the Pacific and we want to stop it spreading any further here.

"MAF Biosecurity New Zealand has no records of it being imported and Landcare Research has no records of this plant ever being in New Zealand prior to this discovery, so it's a new threat to deal with."

Managing invasive knotweed

The ARC will work in partnership with MAF Biosecurity New Zealand to ensure the invasive plant is carefully managed. A response plan for the weed is being prepared.

"Its long, horizontal stems grow deep and wide underground, which helps it spread so vigorously. Like other knotweeds, it can form dense stands that shade and crowd out other vegetation, and displace native species," says Vivienne Lepper.

"We are treating it as a Total Control Pest Plant. We have already started an eradication project on the site where it was found in Glenfield and are working with the residents there.

"We urge people to call us if they think they have Chinese knotweed on their property, rather than trying to control it themselves. As it is a Total Control Pest Plant, we will do the work at no cost to the landowner.

"It's most likely spread through fragments breaking off and re-sprouting into new plants, so people treating it themselves could accidentally spread it further."

The plant is related to other invasive knotweeds found in New Zealand such as Reynoutria japonica (Japanese knotweed) and Reynoutria sachalinensis (giant knotweed).

It is commonly known as Chinese knotweed, liane rouge, red bush or huo tan mu.