Pest Plant Infests Large Southern Site

Tuesday, 23 July 2024, 8:31 pm
Article: Matthew Rosenberg - Local Democracy Reporter

A toxic pest plant capable of smothering whole trees has burst forth at a Southland river site, raising alarm bells at a local council.

Old Man’s Beard is described by Environment Southland as an “extremely aggressive climbing vine” that can reach heights of up to 20 metres.

It can cause lower growing plants to die by cutting off their light, the regional council says, with each plant capable of producing up to 100,000 seeds per square metre.

Last week, a chief executive’s report prepared for a council meeting revealed a “significant” infestation of the plant had been found in willows on the Ōreti River.

The outbreak was deemed large enough to put the council’s containment programme back several years.

Council biosecurity and biodiversity operations manager Ali Meade said the organisation thought Old Man’s Beard was getting under control.

But a trip up the Ōreti River by boat to check a site that was now clear revealed a large infestation slightly further on.

Meade said the site had probably contained the plant for several years, which had invaded a canopy of mature willow trees.

“It’s a big site, the biggest site we’ve seen in Southland for a very long time.”

Managing the removal of the plant could prove difficult, however, because of the importance of the willows to the river system.

While releasing herbicide from a helicopter was an easy solution, it could cause issues for the host plant.

The council was now deciphering how it could kill the Old Man’s Beard without wiping out the willow in the process, or whether it was appropriate to sacrifice the willow.

Spraying the trees was unlikely but remained an option, Meade said.

The containment programme for Old Man’s Beard forms part of the council’s regional pest management plan.

Up to 70 different plant, animal and marine species are included in the plan, with specific containment goals to reduce their habitable area.

There were just over 200 sites in Southland home to Old Man’s Beard, but most were considered small.

Anyone who spots the pest plant is encouraged to get in contact with the council to help control its spread.

LDR is local body journalism co-funded by RNZ and NZ On Air

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