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Alligator weed creeps in to Rangitaiki River

Friday, 13 March 2015 10:00 a.m.

A large infestation of alligator weed (Alternanthera philoxeroides) has been found in the lower Rangitāiki River.

Bay of Plenty Regional Council Land Management Officer Charles Harley said that the find is a serious concern.

“Alligator weed is one of the world’s most damaging weeds. It’s very difficult to control because it has an extremely deep root system. It grows as a dense mat that can choke waterways and dominate pasture in low lying damp areas. It’s also toxic to stock,” he said.

Alligator weed can easily be spread via fragments of plant material in soil, water (fresh and salt) or on machinery.

“Alligator weed is classed as an Eradication and Exclusion pest plant in the Bay of Plenty Regional Pest Management Plan. That means we want to prevent it from becoming established in the region so we’ll lead and fully fund any work that’s needed to do that,” he said.

Mr Harley is asking landowners in the lower Rangitāiki plains to assist by checking their property, drains and current or old kūmara plots for alligator weed. Any finds should be reported to Regional Council by calling 0800 STOP PESTS (0800 780 773) or emailing

Alligator weed is a sprawling perennial plant that has long, hollow, green or red tinged stems and waxy green elliptical shaped leaves. It displays single, white clover-like flowers in summer. A factsheet about alligator weed is available at

“No-one should attempt to control alligator weed themselves, that could make the problem worse. People can help prevent it’s spread though, by keeping earthmoving equipment clean and by leaving all the lower Rangitāiki  flood gates shut unless they have Council’s permission to open them,” Mr Harley said.

The alligator weed discovery was made by Regional Council staff at Reid’s Central Canal during regular maintenance work. Further infestations were found during searches of the wider drainage network and lower Rangitaiki River.

Regional Council staff will start work next week to control the newly discovered infestation, using herbicide.

Alligator weed has also been recorded at four other sites in the eastern Bay of Plenty and a number of small, isolated sites in the western Bay where it is being actively controlled. 

Alligator Weed Close Up highres