Alligator weed control off to promising start

The battle to control Taranaki’s first alligator weed infestation is off to a good start, as Taranaki Regional Council works to stop the highly invasive pest plant from spreading.

Considered one of the world’s worst weeds, alligator weed was confirmed in a lagoon system near Waitara last August.

Before Christmas Council staff treated the land-based weed with herbicide, following up a few weeks later. In early February they tackled the aquatic weed, with two officers wading into the water to spray it directly (below). The weed will be treated twice more before winter sets in – as control is most effective in warmer temperatures.

Council Environment Services Manager Steve Ellis remains “cautiously optimistic” it may be possible to eradicate alligator weed from Taranaki, but the main priority now is to contain it.

“Alligator weed is notoriously tough to get rid of, so we can’t let it take hold as it has in Waikato and other regions.

“With the lagoon being so close to the ocean and a river, it would only take one big storm event to spread the weed fragments or seeds further afield. The work we are doing now reduces the mass of the weed and therefore, reduces that risk.”

He says the Council will have to spray the weed each summer for several years. Other control measures may also be used, including mechanical removal. 

“It won’t be a quick fix but it’s vital we put in the work. The last thing we need is this weed getting out of control and becoming the next hornwort – which is now strangling three Taranaki lakes.”

Signs have been erected at the site warning people to stay out of the lagoon, so as not to inadvertently spread the weed. The public is also asked to be vigilant and report any suspicious plants to the Council on 0800 736 222.

The Council has worked alongside local landowners and residents, Ministry for Primary Industries, Department of Conservation and iwi and hapū to raise awareness and plan the control.


Following further testing, a plant in a private Stratford pond has been confirmed to be the pest plant Senegal tea, not alligator weed as originally believed. It has been treated accordingly.

About alligator weed

The fast-growing alligator weed can grow in both sea and fresh water, where it forms floating mats. It can block waterways, aggravating flooding and impeding access. In pasture, it can out compete more favourable plants and be harmful to animals. It establishes and spreads aggressively from even the smallest stem fragments. It can also grow on land.